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Carrying capacity of U.S. agricultural land: Ten diet scenarios

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Abstract Strategies for environmental sustainability and global food security must account for dietary change. Using a biophysical simulation model we calculated human carrying capacity under ten diet scenarios. The scenarios included two reference diets based on actual consumption and eight “Healthy Diet” scenarios that complied with nutritional recommendations but varied in the level of meat content. We considered the U.S. agricultural land base and accounted for losses, processing conversions, livestock feed needs, suitability of land for crops or grazing, and land productivity. Annual per capita land requirements ranged from 0.13 to 1.08 ha person-1 year-1 across the ten diet scenarios. Carrying capacity varied from 402 to 807 million persons; 1.3 to 2.6 times the 2010 U.S. population. Carrying capacity was generally higher for scenarios with less meat and highest for the lacto-vegetarian diet. However, the carrying capacity of the vegan diet was lower than two of the healthy omnivore diet scenarios. Sensitivity analysis showed that carrying capacity estimates were highly influenced by starting assumptions about the proportion of cropland available for cultivated cropping. Population level dietary change can contribute substantially to meeting future food needs, though ongoing agricultural research and sustainable management practices are still needed to assure sufficient production levels.
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1
Domain Editor-in-Chief
Anne R.Kapuscinski,
Dartmouth
Guest Editor
ErnestoMéndez,
University of Vermont
Knowledge Domain
Sustainability Transitions
Article Type
Research Article
Part of an Elementa
Forum
New Pathways to Sustainability
in Agroecological Systems
Received: October12,2015
Accepted: June14,2016
Published: July22,2016
Carrying capacity of U.S. agricultural land:
Ten diet scenarios
Christian J.Peters1,* JamiePicardy2 Amelia F.Darrouzet-Nardi3 Jennifer L.Wilkins4 Timothy
S.Grin1 Gary W.Fick5
1Friedman School of Nutrition Science and Policy, Tufts University, Boston, Massachusetts, United States
2Geography and Regional Planning, Mount Ida College, Newton, Massachusetts, United States
3Global Health Studies Program, Allegheny College, Meadville, Pennsylvania, United States
4Department of Public Health, Food Studies and Nutrition, Syracuse University, Syracuse, New York, United States
5Section of Soil and Crop Sciences (Emeritus), Cornell University, Ithaca, New York, United States
*Christian.Peters@tufts.edu
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
elementascience.org
Abstract
Strategies for environmental sustainability and global food security must account for dietary change. Using a
biophysical simulation model we calculated human carrying capacity under ten diet scenarios. e scenarios
included two reference diets based on actual consumption and eight “Healthy Diet” scenarios that complied
with nutritional recommendations but varied in the level of meat content. We considered the U.S. agricultural
land base and accounted for losses, processing conversions, livestock feed needs, suitability of land for crops or
grazing, and land productivity. Annual per capita land requirements ranged from 0.13 to 1.08 ha person-1 year-1
across the ten diet scenarios. Carrying capacity varied from 402 to 807 million persons; 1.3 to 2.6 times the
2010 U.S. population. Carrying capacity was generally higher for scenarios with less meat and highest for
the lacto-vegetarian diet. However, the carrying capacity of the vegan diet was lower than two of the healthy
omnivore diet scenarios. Sensitivity analysis showed that carrying capacity estimates were highly inuenced
by starting assumptions about the proportion of cropland available for cultivated cropping. Population level
dietary change can contribute substantially to meeting future food needs, though ongoing agricultural research
and sustainable management practices are still needed to assure sucient production levels.
1. Introduction
1.1 Relationships between diet and sustainability
One of the most perplexing questions in sustainability science is, “What should we eat?” Within the food
and agriculture literature, a strong case has been presented that dietary change is essential for meeting future
human food needs (McMichael et al., 2007; Pelletier and Tyedmers, 2010; Godfray et al., 2010; Foley et al.,
2011; Smith et al., 2013). By “dietary change,” these authors refer to eating patterns that stabilize, or decrease,
livestock production, keep food system environmental impacts within ecosystem limits, and more equitably
distribute food to meet global nutritional goals.
is line of thinking is not new. e equation I=PAT, conceived in the 1970s, proposes that environmental
impact is a function of population, auence, and technology (Parris and Kates, 2003). Calls for considering
the environmental impacts of food consumption through changes in diet were made decades ago both in
popular (Lappé, 1971) and academic literature (Gussow and Clancy, 1986). However, for most of the 20th
Century the predominant agricultural science paradigm focused on increasing yield and production eciency,
expanding in the 1980s and 1990s to include ecological impacts of farming but not focusing on food systems
(Welch and Graham, 1999). Likewise, nutritional sciences and dietary advice over most of the past century
have been guided almost exclusively by evidence on the relationships among nutrients, foods, diets and
human health (King, 2007). If strategies for sustainability must address both food consumption and produc-
tion, then analyses that link agriculture and nutrition are needed.
Carrying capacity of U.S. agricultural land: Ten diet scenarios
2
1.2 Land as a fundamental resource
e food system exerts a broad range of ecological impacts. Biodiversity loss, climate-forcing emissions,
nutrient cycle disruption, and competition for land, water, and energy are all cited as reasons to contain
agriculture’s environmental impact (Godfray et al., 2010; Foley et al., 2011). Among these impacts, land
use is central. Sparing land from conversion to agriculture may be important for protecting biodiversity
(Balmford et al., 2005; Lambin and Meyfroidt, 2011). In addition, as highlighted in debates about the
merits of biofuels, conversion of native grassland or forest to agriculture causes carbon emissions (Fargione
et al., 2008; Searchinger et al., 2008). Both issues provide persuasive arguments against expanding land
under cultivation. Yet agricultural yields are not on track to meet projected global increases in food demand
(Ray et al., 2013). Potential (and probable) increased demand for bioenergy or carbon sequestration further
confounds the land conversion question (Smith et al., 2013). Given all the challenges, understanding the
impact of dietary patterns on land use is critically important.
1.3 Assessing impacts of diet on land use and food supplies
A variety of approaches, each with its own limitations, have been applied to determine how dietary choices
inuence land use. No single method is denitive. Economic models project future demands for food com-
modities and account for competing sectors (van Tongeren et al. 2001), but may not adequately capture supply
side constraints (Heistermann et al., 2006). Life cycle assessments can allocate the environmental impact of
individual foods, but the approach faces methodological challenges and data limitations to modeling com-
plete diets (Heller et al., 2013). A variety of bio-physical approaches exist to estimate the land requirements
of food consumption patterns (see, for example, Gerbens-Leenes et al., 2002; Peters et al., 2007; Wirsenius
et al., 2010), yet this eld is suciently young that comparison of the merits of each approach has not yet
been assessed. Hoekstra and Wiedmann (2014) posit that “cross-fertilization” among dierent environmental
footprint approaches will ultimately lead to more consistent frameworks. In other words, a melding of the
best parts of each approach will occur over time. In the meantime, it is perhaps best to focus on what has
been learned from attempts to understand the relationship between diet and land use.
Two key lessons have emerged from the literature. First, livestock products are a major contributor to land
requirements associated with Western diets (van Dooren et al., 2014). Gerbens-Leenes et al. (2002) developed
one of the rst approaches to estimating land impacts of diet, and compared the land requirements of meeting
current consumption patterns in 14 European countries and the U.S. (Gerbens-Leenes and Nonhebel, 2003).
In all cases, meat, dairy, and fats accounted for the majority of land requirements. Similar patterns have been
observed by subsequent studies of Sweden (Geeraert, 2013) and Germany (Meier and Christen, 2013). While
studies of China (Li et al., 2013) and the Philippines (Kastner and Nonhebel, 2010) suggest that meat, dairy,
and plant oils require a much smaller share of agricultural land, these patterns will likely change over time.
Empirical evidence shows that consumption of meat and dairy products increases as a country’s per capita
income increases (Craneld et al., 1998; Regmi et al., 2001) and that consumption patterns in middle-income
countries are converging with those in higher-income countries (Regmi et al., 2008).
e second lesson is cautionary. While livestock production is the largest land user on Earth, simplistic
thinking about dietary change must be avoided (Herrero and ornton, 2013). Reviews of life cycle assess-
ments of livestock systems and protein products show, denitively, that land use per unit of protein is generally
lower with plant than animal sources (de Vries and de Boer, 2010; Nijdam et al., 2012). However, they also
demonstrate a wide range among individual livestock products and among dierent systems producing the
same livestock product. In addition to this variability in area of land required, the quality of land required
diers as well. Modeling studies suggest that the largest fraction of land needs for ruminant animals are from
forages and grazing lands (Wirsenius et al., 2010; Peters et al., 2014), which are often grown on non-arable
land. us, reducing the most land-intensive products in the diet does not necessarily equate to freeing up
land for cultivation. Finally, the land needs for producing animals do not always follow linear patterns, and
can change rapidly when supplies of residual forage (Keyzer et al., 2005) or oilseed byproducts (Elferink
et al., 2008) have been exhausted. When it comes to interpreting the land impacts of dietary change, caution
is warranted.
1.4 Purpose of this analysis
e purpose of this analysis is to compare the per capita land requirements and potential carrying capacity of
the land base of the continental United States (U.S.) under a diverse set of dietary scenarios. We argue that
assessing human carrying capacity (persons fed per unit land area) is essential for fully understanding current
and potential productivity of a land base. Estimates of carrying capacity represent the productive output of
many crops grown across a heterogeneous land base in a single indicator, the number of people fed. While
trade will remain essential to national food security in many countries, the purpose behind the closed
system approach was to conduct a complete accounting of all land needed to meet total food needs and,
thus, calculate carrying capacity.
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
Carrying capacity of U.S. agricultural land: Ten diet scenarios
3
ree aspects of this paper are novel relative to prior work. First, the study focuses at the scale of the
conterminous U.S. To our knowledge, such an analysis of how dietary change might impact land use and
carrying capacity has not been conducted at this scale. Second, the “Foodprint model” (described below)
estimates land requirements for complete diets, accounting for three important interactions: the multiuse
nature of certain grain and oilseed crops, the suitability of multiple land types to grazing, and the relation-
ship between dairy production and beef production. Finally, the study explores how assumptions about the
partitioning of agricultural land and the suitability of cropland for cultivated crops inuences estimates of
carrying capacity.
2. Materials and methods
2.1 Overview of the approach
A biophysical simulation model (the U.S. Foodprint Model based on Peters et al., 2007) that represents the
conterminous U.S. as a closed food system was designed to calculate the per capita land requirements of human
diets and the potential population fed by the agricultural land base of the continental United States. To do
this, three sets of calculations were performed (Fig. 1). e rst set of calculations estimated the annual, per
capita food needs of the population based on daily food intake, the individual food commodities that comprise
each food group, the weight of a serving of food, losses and waste that occur across the food system, and the
conversion of raw agricultural commodities into processed food commodities. e second set of calculations
estimated the individual land area required for each agricultural commodity in the diet based on yield data
for each component crop and the feed requirements of all livestock. e third set of calculations estimated
the potential carrying capacity of U.S. agricultural land, accounting for the aggregate land requirements of
a complete diet, the area of land available, and the suitability of land for dierent agricultural uses. At key
points in these calculations, marked with an asterisk in the diagram, additional calculations were performed to
account for interdependencies in the food system. A description of the primary calculations and data sources
is described below, and additional detail is provided in the Supplementary material.
2.2 Scenarios of food consumption
Ten distinct diet scenarios were analyzed in this study (Table 1). e scenarios focused solely on dierences
in food consumption patterns; parameters for food losses and waste, processing conversions, livestock feed
needs, crop yields, land availability, and land suitability were held constant. e structure of the scenarios was
designed to compare the land requirements and carrying capacity of nine isocaloric (equal caloric content)
diets, eight of which are comparable in nutritional quality but which dier in terms of their protein sources.
e tenth diet, representing current average food consumption, was included as a reference point. e rela-
tionship between the scenarios is described in more detail below.
e reference diet (Baseline) reects contemporary food consumption patterns based on loss-adjusted
food availability data from 2006–2008 (USDA Economic Research Service, 2010). e rst isocaloric diet
is identical to the baseline for the major food groups, but contains fewer discretionary calories in the form
of added fats and sweeteners to prevent energy intake from exceeding caloric needs (Positive control, POS).
e eight remaining diet scenarios generally conform to the USDA food group recommendations published
in the 2010 Dietary Guidelines for Americans (U.S. Department of Agriculture and U.S. Department of
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
Figure 1
Flow diagram of the sets of
calculations performed in the
U.S. Foodprint model.
Major calculations are represented
by the large boxes and the
underlying data are indicated by
smaller boxes beneath. Arrows
indicate the ow of data from
one set of calculations to another.
e asterisks (*) mark points
where additional calculations are
made.
doi: 10.12952/journal.elementa.000116.f001
Carrying capacity of U.S. agricultural land: Ten diet scenarios
4
Health and Human Services, 2010), hereafter referred to as the dietary guidelines. Each diet includes the
weighted average recommendation for the U.S. population, based on the age-gender distribution of the
population and each cohort’s respective food group and caloric recommendations. e single exception is
the dairy food group, which did not meet the recommended level in all diets. Dairy was selected because its
recommendation is driven by dietary reference intakes for calcium, which can also be obtained from plant
sources, fortied foods, or supplements, and all diets already contained adequate amounts of dietary protein.
Five of the “Healthy Diet” scenarios contained meat, and three were vegetarian. e diets containing meat
(omnivore diets) represent varying degrees of transition toward plant-based sources of protein. e 100%
healthy omnivorous diet represents a situation in which all Americans follow the dietary guidelines, requir-
ing a modest (13%) reduction in protein-rich foods but retaining the current preference for meat (red meat,
poultry, and sh) as the primary protein sources. e next four diets represent a transition toward vegetarian
eating patterns (80%, 60%, 40%, and 20% healthy omnivorous), in which a decreasing percentage of meals
follow the healthy omnivorous diet and are replaced by meals following an ovolacto-vegetarian diet. Eectively
meat is substituted with additional servings of eggs, nuts, pulses, and tofu. e nal three scenarios represent
distinct vegetarian diet patterns: ovo-lacto vegetarian (OVO), lacto vegetarian (LAC), and vegan (VEG).
Within each of the ten diet scenarios, foods were divided into ve major groups (grains, vegetables, fruits,
dairy, and protein-rich foods) and two discretionary categories (added fats and sweeteners). Vegetables were
further divided into subgroups as done in the dietary guidelines. In addition, the dairy and fats groups were
broken into subgroups. e dairy group distinguishes uid products (e.g. milk and yogurt) from other prod-
ucts (e.g. cheese and ice cream) as a heuristic way to enable the scenarios to represent dietary guidelines to
choose lower fat sources of dairy. Similarly, plant sources of added fats were separated into plant oils (which
are generally encouraged) and animal sources (which are recommended only in moderation). Protein rich
foods were reported individually and in subgroups of similar foods (e.g. dry beans, peas, and lentils) because
the literature suggests that these foods vary signicantly in terms of their individual land requirements.
Daily intake of the major food groups, food subgroups, and protein foods for each of the ten diet scenarios
are reported in Table 2.
e macronutrient proles of the ten diets diered in two important ways (Table 3). First, while the base-
line diet represented current per capita energy intake, all other diets were balanced to meet the age-gender
weighted average caloric requirements of the U.S. population, roughly 2,150 kcal person-1 day-1. Second, the
nine isocaloric diets diered in terms of total protein, fat, and carbohydrate content. Diets with higher levels
of animal-based foods contained higher levels of protein and fats, and less carbohydrate, than diets that were
more plant-based.
2.3 Partitioning of agricultural land
In this analysis, the term “land requirements” refers to the area of productive agricultural land needed to
supply food, meaning land harvested by hand, machine, or grazing animals. Productive agricultural land was
divided into two pools, cropland and grazing land. Cropland includes all land harvested for crops and arable
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
Table 1. Scenarios for the land requirements of diet analysis of the U.S.
Group Description Name Symbol Key attributes
Current
consumption
Based on USDA
estimates of per capita
loss-adjusted food
availability.
Baseline BAS Food intake equals loss-adjusted food availability
for individual food commodities.
Positive control POS As above, except intake of fats and sweeteners is
reduced to make diet energy-balanced.
Healthy diet,
omnivorous
Complies with 2010
Dietary Guidelines for
Americans. Includes
animal esh.
100% healthy
omnivorous
OMNI
100
100% of person-meals follow an omnivorous
healthy diet pattern.
80% healthy
omnivorous OMNI 80
80% of person-meals follow an omnivorous healthy
diet pattern and 20% follow a ovo-lacto vegetarian
healthy diet pattern.
60% healthy
omnivorous OMNI 60
60% of person-meals follow an omnivorous healthy
diet pattern and 40% follow a ovo-lacto vegetarian
healthy diet pattern.
40% healthy
omnivorous OMNI 40
40% of person-meals follow an omnivorous healthy
diet pattern and 60% follow a ovo-lacto vegetarian
healthy diet pattern.
20% healthy
omnivorous OMNI 20
20% of person-meals follow an omnivorous healthy
diet pattern and 80% follow a ovo-lacto vegetarian
healthy diet pattern.
Healthy diet,
vegetarian
Complies with 2010
Dietary Guidelines for
Americans.
Excludes animal esh.
Ovolacto vegetarian OVO Includes both eggs and dairy products.
Lacto vegetarian LAC Includes dairy products. Excludes eggs.
Vegan VEG Excludes all livestock products.
doi: 10.12952/journal.elementa.000116.t001
Carrying capacity of U.S. agricultural land: Ten diet scenarios
5Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
Table 2. Daily food intake by diet scenarioa
Food
group
Food subgroup Unit BAS POS OMNI
100
OMNI
80
OMNI
60
OMNI
40
OMNI
20
OVO LAC VEG
Grains Whole and rened grains oz 7.66 7.66 7.01 7.01 7.01 7.01 7.01 7.01 7.01 7.01
Vegetables Total vegetables cups
Dark green vegetables cups 0.16 0.16 0.26 0.26 0.26 0.26 0.26 0.26 0.26 0.26
Red and orange vegetables cups 0.30 0.30 0.82 0.82 0.82 0.82 0.82 0.82 0.82 0.82
Dry beans, lentils, and peas cups 0.11 0.11 0.26 0.26 0.26 0.26 0.26 0.26 0.26 0.26
Starchy vegetables cups 0.46 0.46 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80
Other vegetables cups 0.53 0.53 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65
Fruits All fruit cups 0.86 0.86 1.92 1.92 1.92 1.92 1.92 1.92 1.92 1.92
Dairy All dairy cups
Cow’s milk products cups 1.68 1.68 1.68 1.77 1.85 1.94 2.02 2.11 2.25 0.00
Fluid milk and yogurt cups 0.68 0.68 1.43 1.50 1.58 1.65 1.72 1.79 1.92 0.00
Cheese and other dairy cups 1.00 1.00 0.25 0.26 0.28 0.29 0.30 0.31 0.34 0.00
Soy milk cups n/a n/a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2.89
Protein All protein foods meat oz equivalents 6.67 6.67 5.80 5.80 5.80 5.80 5.80 5.80 5.80 5.80
Dry beans, lentils, and peas meat oz equivalents n/a n/a 0.00 0.25 0.51 0.76 1.01 1.26 1.53 2.02
Nuts meat oz equivalents 0.77 0.77 0.67 0.91 1.16 1.40 1.65 1.89 2.29 2.29
Tofu meat oz equivalents n/a n/a 0.00 0.33 0.66 0.98 1.31 1.64 1.98 1.48
Beef meat oz equivalents 1.80 1.80 1.56 1.25 0.94 0.62 0.31 0.00 0.00 0.00
Pork meat oz equivalents 1.19 1.19 1.03 0.83 0.62 0.41 0.21 0.00 0.00 0.00
Chicken meat oz equivalents 1.51 1.51 1.31 1.05 0.79 0.53 0.26 0.00 0.00 0.00
Turkey meat oz equivalents 0.39 0.39 0.34 0.27 0.21 0.14 0.07 0.00 0.00 0.00
Eggs meat oz equivalents 0.53 0.53 0.46 0.57 0.68 0.79 0.89 1.00 0.00 0.00
Fish meat oz equivalents 0.48 0.48 0.42 0.33 0.25 0.17 0.08 0.00 0.00 0.00
Added fats Plant oils grams 64.46 28.03 28.03 28.03 28.03 28.03 28.03 28.03 28.03 28.03
Dairy fats grams 7.26 2.14 1.09 1.09 1.09 1.09 1.09 1.09 1.09 0.00
Animal fat (lard and tallow) grams allowed in
diet
2.90 0.86 0.44 0.35 0.26 0.17 0.09 0.00 0.00 0.00
Sweeteners All sweeteners tsp 28.91 8.53 4.34 4.34 7.23 4.34 4.34 4.34 4.34 4.34
aEach scenario is indicated by its alphanumeric code: BAS (baseline), POS (positive control), OMNI 100 (100% healthy omnivorous),
OMNI 80 (80% healthy omnivorous), OMNI 60 (60% healthy omnivorous), OMNI 40 (40% healthy omnivorous), OMNI 20 (20%
healthy omnivorous), OVO (ovolacto vegetarian), LAC (lacto vegetarian), and VEG (vegan). Scenario descriptions are provided in the
main text.
doi: 10.12952/journal.elementa.000116.t002
land that was used as pasture. Grazing land is unsuitable for cultivation and includes permanent pasture,
rangeland, and woodland pasture. ese two pools included most land that occurs on farms. However, they
excluded idle cropland, woodlots not used for grazing, and land in farm roads, structures, ponds, and all
other uses. e relationship between the categories used in this analysis and the standard land use categories
employed by USDA is discussed in detail in the Supplementary material (Text S1, “Land availability” section).
Cropland was further partitioned to limit the percentage of the total area that can be used for cultivated
crops in a given year. Scientists have long recognized that soils vary in their inherent suitability for intensive
agriculture. e U.S. land capability classication system was rst developed in the 1930s and rened over
several decades to categorize land into grades based on their suitability for agriculture (Helms, 1997). e
system distinguishes between arable land, land suitable only for grazing or forestry, and land entirely
unsuited to commercial plant production. It further divides arable land into four grades (Classes I through IV).
Sustainable land management on all but Class I soils (the highest grade of arable land) requires attention to
crop choice or production practices, and these requirements become increasingly restrictive at each change
in capability class (see USDA Natural Resources Conservation Service, 2013).
Decisions about the specic practices or crop choices will vary from farm to farm. Nonetheless, empirical
data from the 2012 National Resources Inventory (U.S. Department of Agriculture, 2015) show that since
1982 large areas of cropland have been dedicated to permanent hay crops (15 to 19 million ha) or to hay
crops and pasture grown in rotation with annual crops (4.3 to 8.7 million ha). Data from the Major Land
Uses program (USDA Economic Research Service, 2011) show that an additional 5.2 to 27 million ha of
Carrying capacity of U.S. agricultural land: Ten diet scenarios
6
cropland have been used exclusively as pasture. Taken together, the area in perennial forages has ranged from
20 to 30 percent of total productive cropland (authors’ calculations from USDA, 2015 and USDA Economic
Research Service, 2011).
Estimating the optimum combination of annual to perennial crops on U.S. cropland to control erosion and
maintain adequate soil health lies beyond the scope of this paper. A baseline estimate of the limit on cultivated
crops was made based on the current proportion of cropland under cultivation. Since this assumption
could potentially limit the carrying capacity of the model scenarios, a sensitivity analysis was included to
examine the inuence of increasing or decreasing the limit on cultivated cropland. Carrying capacity for the
eight healthy diet scenarios was estimated for seven dierent levels of the restriction on cultivated cropland.
One level was the default value, 95 out of 134 million ha of cropland (71% of the total cropland area). e
other six levels represented increases or decreases in the default value in 10% increments.
2.4 Model calculations
e U.S. Foodprint model was organized as a stand-alone, spreadsheet-based model (Text S1, “Model structure”
section). All calculations were performed simultaneously in Excel ® but can be understood, conceptually, as
three sets of interrelated calculations. e principal calculations are described below in three sections: food
needs, land requirements, and carrying capacity.
2.4.1 Food needs
Diet scenarios were structured based on intake of food groups, as shown in Table 2. e rst set of calcula-
tions performed in the U.S. Foodprint model translated each of the diet scenarios into estimates of the mass
of primary food commodities needed to supply each diet, as well as the equivalent quantities of agricultural
commodities from which the foods are derived.
e quantity of primary food commodities (QF) required in a diet (in g person-1 year-1) was the product of
ve factors (Eq. 1). Intake (I) of a food or food group (i) was dened for each of the scenarios, and expressed
in servings person-1 day-1. For composite food groups, composition (C) estimated the proportion of intake that
come from individual food commodities (j) based on the relative loss-adjusted availability of these foods in
the U.S. food supply for the period 2006–2008 (USDA Economic Research Service, 2010). Weight (W ) of a
serving converted intake from a volume basis to a mass basis (expressed in g serving-1) using data on serving
size from the Nutrient Database for Standard Reference, Release 23 (USDA Agricultural Research Service,
2010). Loss adjustment factors (L) accounted for spoilage, waste, inedible portions, and cooking losses using
data from the USDA Loss-Adjusted Food Supply Database (USDA Economic Research Service, 2010). e
constant 365 converts daily consumption to annual consumption.
e quantities of food required were converted into equivalent amounts of agricultural commodities (Eq. 2)
to enable subsequent calculations of land requirements using crop yield data. e quantity (g person-1 yr-1)
of agricultural commodity (QA) required to supply food intake was the product of the quantity of food com-
modity required (QFj) and a processing conversion (P) which converts units of primary food commodity
(j) output into the equivalent amount of agricultural commodity (k) input. Processing conversion factors
were obtained primarily from U.S. Department of Agriculture sources (USDA Economic Research Service,
1992 and 2010) with a few exceptions where data were not available (Text S1, Table S2). However, dairy
products constituted a special case, since the amount of uid milk required to make them depends on the
aggregate requirements for milk fat and non-fat solids relative to the composition of the milk. erefore, the
QFij = Ii × Cij × Wj × Lj × 365 (1)
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
Table 3. Macronutrient prole of diet scenarios
Scenario name Scenario symbol Total energy
(kcal day-1)
Protein
(g day-1)Fat (g day-1) Carbohydrate (g day-1)
Baseline BAS 2,844 92.1 119.8 363.1
Positive control POS 2,153 91.9 80.9 272.6
100% healthy omnivorous OMNI 100 2,153 88.7 73.0 296.8
80% healthy omnivorous OMNI 80 2,153 86.5 72.5 301.4
60% healthy omnivorous OMNI 60 2,153 84.2 72.0 306.1
40% healthy omnivorous OMNI 40 2,153 82.0 71.5 310.8
20% healthy omnivorous OMNI 20 2,153 78.9 71.0 315.4
Ovolacto-vegetarian OVO 2,153 77.5 70.5 320.1
Lacto-vegetarian LAC 2,154 75.7 69.7 325.6
Vegan VEG 2,154 74.0 65.8 336.2
doi: 10.12952/journal.elementa.000116.t003
Carrying capacity of U.S. agricultural land: Ten diet scenarios
7
model determined the aggregate milk fat and non-fat solid requirements for all dairy products included in
each diet scenario, then processing conversions were calculated based on the limiting component (see Text
S1, “Processing conversions for dairy products” section).
2.4.2 Land requirements
e second set of calculations determined the land requirements for individual foods and for complete diets.
2.4.2.1 Individual foods. Annual per capita land requirements (LR) for individual foods were calculated (in ha yr-1)
based on the quantities of agricultural commodities needed to support food intake and estimates of the
respective agricultural yields. For plant-based foods (Eq. 3a), the land requirement (LR) for each individual
food commodity (j) equaled the quantity (QA) of agricultural commodity (k) required (in kg yr-1) divided by
the average U.S. yield (Y) of that commodity (in kg ha-1) over the time period 2000-2010. In this equation,
agricultural commodities are synonymous with crops.
Annual per capita land requirements for animal-based foods were calculated for each individual feed ingredi-
ent (Eq. 3b). e land area required (LR) for each feed ingredient (l) needed to produce an animal-based food
(j) is equal to the quantity of feed crop needed divided by the associated crop yield. e quantity required
of each individual feed crop equals the product of three factors: the quantity (QA) of agricultural commodity
(k) required supply the food in the diet (in kg yr-1), the amount of feed ingredient (l) in the ration (R) fed to
livestock (in kg feed kg livestock product-1) and a conversion factor (P) to account for any processing losses
in deriving the feed ingredient from the source crop (e.g. soybean meal from soybean (Glycine max)). e
quantity of feed crop required is divided by the yield of the crop (in kg ha-1) to calculate land requirements.
Yield data (in kg ha-1) for harvested crops for the period 2000–2010 were based on annual surveys conducted
by the USDA National Agricultural Statistics Service. Data were compiled from the QuickStats Database
(USDA National Agricultural Statistics Service, 2014) and various summary reports (USDA National Agri-
cultural Statistics Service, 2004, 2008a, 2008b, 2010a, 2010b, and 2011; USDA National Agricultural Statistics
Service - California Field Oce, 2011). Biomass productivity of grazing lands is not reported in USDA
yields statistics, and a separate procedure was used to estimate forage yields from grazed land (see Text S1,
“Grazing yields” section and Table S1). e feed needs of livestock products (beef, chicken, dairy, eggs, pork,
and turkey) were obtained from a model developed by Peters et al. (2014) for the purpose of calculating feed
conversion ratios and aggregate ration compositions based on contemporary production practices in the U.S.
e model estimated feed needs for a simplied list of ingredients: alfalfa silage, corn grain, corn silage, grass
hay, grazed forage, and soybean meal. Conversions from feed ingredients to crop ingredients were determined
from various USDA sources (see Text S1, “Data sources and assumptions” section).
An important food system interaction considered at this stage was that the beef supply chain includes
meat from animals that originate in the dairy system. Culled dairy animals, veal calves, and dairy calves that
are raised to market weight contribute to the total beef supply. e model determined the proportion of meat
that comes from beef versus dairy breeds based on the residual meat output from the dairy system and the
quantities of beef and uid milk required in each diet scenario (see Dataset S1).
2.4.2.2 Complete diets. Land requirements for complete diets were calculated for three distinct categories
of land: cropland in cultivated crops, cropland in perennial forage crops, and grazing land (Eqs. 4a-4c).
Cultivated cropland included all annual eld crops, fruits, nuts, and vegetables. Cropland in perennial for-
ages included hay crops and grazing on land which could be cropped but is used for pasture. Grazing land
included non-arable grasslands and woodlands that can be used for grazing. Preliminary estimates of the
land requirements of each diet for each category of land were calculated by summing the land requirements
for individual food commodities, grouped by the appropriate land class.
For cultivated cropland (Eq. 4a), aggregate land requirements (ALR) of diet (ha person-1 yr-1) were calculated
by taking the sum of all land requirements (LR) for individual plant-based foods (jk) and the land require-
ments of ration ingredients (jkl) used in producing animal-based foods that are cultivated crops.
A multi-use crop adjustment (MUCA), which accounts for the multi-use nature of oilseed crops and corn
(Zea mays), was subtracted from this subtotal. Preliminary estimates of aggregate land requirements (ALR)
QAjk = QFj × Pjk (2)
LRjk = QAjk / Yk(3a)
LR jkl = (QAjk × R kl × P kl) / Y l(3b)
ALRperennial cropland = ∑ (LRjkl) + GAperennial cropland (4b)
ALRcultivated cropland = ∑ (LRjk) + ∑ (LRjkl) – MUCA (4a)
ALRgrazing = ∑ (LRjkl) – GAgrazing (4c)
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
Carrying capacity of U.S. agricultural land: Ten diet scenarios
8
for perennial cropland (Eq. 4b) and grazing land (Eq. 4c) were calculated as the sum of the land requirements
of certain livestock ration ingredients, specically, hay crops, perennial silage crops, and grazed forages. Since
grazed forages can also be produced on cropland, the subtotals of the land requirements of individual ration
ingredients were modied by applying a grazing adjustment (GA), to distribute grazed forage requirements
across both cropland and grazing land to optimize use of available land. For details on the calculations to
derive the multi-use crop adjustment and the grazing adjustment, see the Supplementary material (Text S1,
“Land use adjustments” section).
2.4.3 Carrying capacity
In this study, the term “carrying capacity refers to the number of people that could be fed from an agricul-
tural land base. Potential carrying capacity was calculated based on per capita land requirements, the areas of
cultivated cropland, perennial cropland, and grazing land available in the U.S, and the suitable uses for each
pool of land. Only land that is harvested for crops or used for livestock grazing was considered available for
food production. While the practice of agriculture also involves support land, such as buildings, farm roads,
and irrigation ponds, such uses do not generate biomass and were therefore excluded from the estimate of
available land.
Availability of cropland for cultivated crops and perennial forages was estimated from data on land use for
farms, crop groups, and individual crops from the 2007 Census of Agriculture (USDA National Agricultural
Statistics Service, 2009) (see Text S1, “Land availability” section). e existing ratio of cultivated to perennial
forage crops was used to set an upper bound on the area of cropland considered suitable for cultivated crop-
ping. Cultivated cropland was further multiplied by a cropping intensity factor to account for the eective
area that may be harvested in a single year. All non-cropland used for grazing in 2007 was considered avail-
able grazing land. Estimates of the combined area of public and private land used for grazing in 2007 were
obtained from the data set “Major Uses of Land in the U.S.” (USDA Economic Research Service, 2011).
Both grassland and grazed woodlands were included.
e carrying capacity of the U.S. (persons potentially fed) under each diet scenario was calculated based
on the per capita land requirements for each pool of land and the corresponding areas of land available in
the U.S. (Eq. 5). In theory, the potential to meet food needs will be limited by the most scarce pool (or pools)
of land. us, carrying capacity was calculated using a function that returns the minimum of three possible
values: (a) the eective area (EA) of available cultivated cropland divided by the annual per capita land
requirements (ALR) for cultivated cropland, (b) the available area (A) of cropland divided by the sum of the
annual per capita land requirements (ALR) from cultivated and perennial cropland, and (c) the total area of
available cropland and grazing land divided by the sum of the annual per capita land requirements (ALR)
for cultivate cropland, perennial cropland, and grazing land.
3. Results
3.1 Overview of results
e ndings of this study build upon one another sequentially. Estimates of the annual per capita land
requirements of complete diets are foundational and are thus presented rst (section 3.2). Assumptions
regarding the area of agricultural land available in each pool and the utilization of available land are discussed
next (section 3.3). Carrying capacity of the U.S. agricultural land base is compared across each diet scenario
in the nal section (3.4).
3.2 Land requirements of diet
Total per capita requirements for agricultural land varied widely across the diet scenarios, with a factor of eight
separating the least land intense and most land intense diets (Fig. 2). e baseline scenario had the highest
total land use, 1.08 ha person-1 year-1, followed closely by the positive control, 1.03 ha person-1 year-1. Land
requirements decreased steadily across the ve healthy omnivorous diets, from 0.93 to 0.25 ha person-1 year-1,
and the total land requirements for the three vegetarian diets were all similarly low, 0.13 to 0.14 ha person-1
year-1. However, dierences in total per capita land requirements are only part of the story.
Dierent patterns of variation were also observed between the three pools of land. Per capita requirements
for grazing land accounted for a large portion of the variation across the diets ranging from 0.10
to 0.74 ha person-1 year-1across the seven diet scenarios that included meat. Grazing land was absent from
the three vegetarian diets. Likewise, annual per capita requirements for perennial cropland ranged widely.
Perennial cropland requirements were highest for the baseline and positive control diets (0.16 and 0.17 ha
person-1 year-1), and perennial cropland requirements decreased steadily as the amount of meat in the diet
decreased, eventually leveling o to 0.02 ha person-1 year-1 for the ovolacto- and lacto-vegetarian diets. Perennial
Carrying capacity = MIN (EAcultivated cropland / ALRcultivated cropland, Acropland /(ALR cropland +
ALR perennial cropland), A total / (ALRcultivated cropland + ALRperennial cropland + ALR grazing)) (5)
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
Carrying capacity of U.S. agricultural land: Ten diet scenarios
9
cropland requirements were zero in the vegan diet. In contrast, the variations in per capita requirements for
cultivated land were less pronounced relative to grazing land and perennial cropland. Cultivated cropland
requirements displayed a 1.5-fold range across the diet scenarios, from a high of 0.18 ha person-1 year-1 in the
baseline diet and a low of 0.12 ha person-1 year-1 in the lacto-vegetarian diet.
3.3 Utilization of available land
To calculate potential carrying capacity, all diet scenarios were restricted to the areas available within each
pool of productive agricultural land. e aggregate area available for food production was estimated to be
95 million ha cultivated cropland, 134 million ha total cropland, and 299 million ha grazing land (Dataset S1).
Aggregate land use in each scenario was estimated as the product of carrying capacity and the annual per
capita land requirements.
Not all diets equally exploited each pool of land (Fig. 3). e ve diets containing the largest quantities
of meat (baseline, positive control, 100% health omnivorous, 80% healthy omnivorous, and 60% healthy
omnivorous) used the entire available area, both cropland and grazing land. e ve diets containing the
least meat (or no meat) used the maximum allowable area of cultivated cropland and varied widely in their
use of the remaining agricultural land. e 40% healthy omnivorous diet and the 20% healthy omnivorous
diet used some of the available grazing land (214 and 75 million ha, respectively) and most of the cropland
restricted to perennial forages (35 and 24 million ha, respectively). e ovolacto- and lacto-vegetarian diets
used about half of the cropland restricted to perennial forages, while the vegan diet used none of the restricted
cropland. None of the vegetarian diets used any grazing land (dairy rations were modeled with cows fed only
harvested feeds and forages, see Peters et al., 2014).
Dierences in land allocation were even more noticeable when land use was compared by crop group
(Fig. 4). In the two diets closest to current consumption patterns (baseline and positive control), approximately
20% of the available cropland was devoted to food crops (grains, fruit, vegetables, pulses, nuts, and sweeten-
ers) and about 80% to primarily feed and forage crops (feed grains, oilseeds, hay, and pasture). Food crops
constituted an increasing share of cropland use as the amount of meat in the diet was reduced.
3.4 Potential carrying capacity
Human carrying capacity is dened here as the number of people who could be fed from the area of land
available to produce the food required for each diet scenario. is number was a function of the annual per
capita land requirements and the area of land available in each pool within the U.S. Potential carrying capacity
of the U.S. varied substantially across the scenarios, with a factor of two separating the highest and lowest
carrying capacities (Table 4). e baseline diet had the lowest estimated carrying capacity (402 million per-
sons), and the lacto-vegetarian diet had the highest (807 million persons). All estimates exceeded the 2010
U.S. population (U.S. Census Bureau, 2015). Indeed, model output estimated that U.S. agricultural land has
the capacity to meet the needs of a populace 1.3 to 2.6 times larger than the 2010 population, without trade.
All dietary changes increased estimated carrying capacity relative to the baseline. Reducing excess dis-
cretionary calories (positive control diet) resulted in a small increase in potential to feed people, 19 million
persons (about 5% of the 2010 U.S. population). Reducing meat in the diet, as shown by the ve healthy
omnivorous diet scenarios, further increased carrying capacity relative to the baseline: 63 to 367 million
persons (16% to 91% of the 2010 U.S. population). Switching to an entirely vegetarian diet also increased
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
Figure 2
Annual per capita requirements
for productive agricultural land
by diet scenario and category of
land use.
Diets are described in detail in
text and Table 1.
doi: 10.12952/journal.elementa.000116.f002
Carrying capacity of U.S. agricultural land: Ten diet scenarios
10
carrying capacity relative to the baseline, though ovolacto- and lacto-vegetarian diets had higher carrying
capacities than the vegan diet. Indeed, the carrying capacity of the vegan diet fell between the 60% omnivore
and 40% omnivore diet.
A sensitivity analysis was run to demonstrate how the restriction on the area of cultivated cropland inu-
ences estimated carrying capacity (Fig. 5). Carrying capacity was shown to be highly sensitive to the starting
assumptions about the proportion of land available for cultivated cropping. e dierences in carrying
capacity observed across the eight diets were smaller when less of the cropland is available for cultivation
and larger when more land is available for cultivation. Each diet, except the vegan diet, eventually reached
a plateau, indicating the point at which the proportion of land available for cultivated cropping exceeds the
level needed for cultivated crops. Over the range observed, the vegan diet eventually surpasses all but the
lacto-vegetarian diet. ese two diets are approximately equal when 92% of cropland is considered avail-
able for cultivation.
4. Discussion
4.1 Inuence of dietary patterns on agricultural land requirements
ree lessons can be gleaned from the data presented. First, requirements for grazing land must be distin-
guished from requirements for cropland. As shown in Fig. 2, annual per capita requirements for agricultural
land exhibit a wide (eight-fold) range across scenarios. A simple comparison of the total land requirements
could lead one to the erroneous conclusion that the dierences in carrying capacity are similarly large.
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
Figure 3
Utilization of the area of cropland
available for food production in
the United States by diet scenario.
Diets described in detail in text
and Table 1.
doi: 10.12952/journal.elementa.000116.f003
Figure 4
Distribution of cropland use by
crop type.
Bars indicate the percentage of
total cropland devoted to major
categories of crops as dened by
use within the food system. Diets
described in detail in text and
Table 1.
doi: 10.12952/journal.elementa.000116.f004
Carrying capacity of U.S. agricultural land: Ten diet scenarios
11Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
However, grazing land by denition is not arable, and the estimated forage yield for this resource is quite low.
us, the estimates of per capita land requirements are only meaningful when divided into constituent pools.
Second, diet composition greatly inuences overall land footprint. As Fig. 3 illustrates, ve of the diets
operate under conditions in which the total footprint of agriculture does not change, even though carrying
capacity diers widely. However, the 40% healthy omnivorous, the 20% healthy omnivorous, and the three
vegetarian diets all have aggregate footprints smaller that the area currently used in the U.S. is nding is
signicant in light of recent calls to contain the footprint of agriculture (Godfray et al., 2010; Foley et al.,
2011). Provision of food, while essential, is not the only important ecological service provided by land. Some
of these services, such as carbon capture, may be compatible with grazing, at least in well-managed systems.
Other services, such as wildlife habitat, may be impinged where domesticated species compete for biomass
with wild ruminants and ungulates. Finally, the use of perennial cropland for grazing or hay production
could conceivably compete with bioenergy production where biomass energy or draft animals are possible
alternatives to fossil fuels.
ird, dietary changes toward the 2010 Dietary Guidelines for Americans imply very dierent alloca-
tions of land by crop type. Specically, land in grains, fruits and vegetables, pulses, and nuts would need to
increase relative to land in feed grains and oilseeds, hay, and cropland pasture. USDA researchers have noted
the implications of compliance with the dietary guidelines (Young and Kantor, 1999; Buzby et al., 2006),
and these patterns are even more striking under scenarios of reduced meat consumption. In short, scenarios
that dier from the baseline represent increasingly large shifts from the status quo and would have implica-
tions well beyond land use. While such considerations lie beyond the purpose of this study, it is essential to
recognize that shifts toward plant-based diets may need to be accompanied by changes in agronomic and
horticultural research, extension, farm operator knowledge, infrastructure, livestock management, farm and
food policy, and international trade.
Table 4. Carrying capacity of the U.S. by diet scenario
Scenario Population fed Change from baseline
Symbol (108 persons) (% of 2010 population)a(108 persons) (% of BAS population)
BAS 4.02 130% na na
POS 4.21 136% 0.19 5%
OMNI 100 4.67 151% 0.63 16%
OMNI 80 5.48 178% 1.46 36%
OMNI 60 6.69 217% 2.67 66%
OMNI 40 7.52 244% 3.50 87%
OMNI 20 7.69 249% 3.67 91%
OVO 7.87 255% 3.84 96%
LAC 8.07 261% 4.05 101%
VEG 7.35 238% 3.32 83%
aPopulation of the United States on April 1, 2010 according to the 2010 Census (U.S. Census Bureau, 2015).
doi: 10.12952/journal.elementa.000116.t004
Figure 5
Sensitivity of carrying capacity to
starting assumptions regarding
the proportion of cropland
available for cultivation.
Solid lines indicate vegetarian
diet scenarios and dashed lines
indicate omnivore diet scenarios.
Diets are described in detail in
text and Table 1. Proportion
of land available for cultivated
cropping covers a range around
the default value used in previous
model runs (0.71). See section 2.3
for more details.
doi: 10.12952/journal.elementa.000116.f005
Carrying capacity of U.S. agricultural land: Ten diet scenarios
12
4.2 Interpreting potential carrying capacity
In this study, carrying capacity is an estimate of the potential population that could be fed from an agricultural
land base. Our use of the term deviates somewhat from its broader meaning in ecology, in which a species’
population may be limited by any essential resource, not just access to food. Nonetheless, carrying capacity
provides a valuable concept for measuring the potential food output of agricultural land. Our use of the concept
is consistent with arguments in the literature (Peters et al., 2003; Cassidy et al., 2013) that from the standpoint
of nutrition, productivity of agricultural land is more appropriately measured in people fed per unit area than
by yield of individual crops. is analysis held crop yields constant across all scenarios. us, the reported
estimates of potential carrying capacity measured only the dierences imposed by changing consumption.
Seen in this light, the estimates of carrying capacity for each scenario suggest that dietary choices can greatly
inuence the ability of agriculture to meet human food needs. Reducing meat in the diet clearly resulted in
increased carrying capacity, as evidenced by the fact that carrying capacity increased across the ve healthy
omnivorous diets as the amount of meat consumed decreased. Likewise, the ovolacto- and lacto-vegetarian
diets had the highest estimates of carrying capacity overall. However, the inuence of dietary changes are
not always obvious, as shown by the fact that the relative position of the vegan diet varied depending on
starting assumptions regarding the proportion of cropland available for cultivation. Similarly, removing 700
kcal person-1 day-1 from the baseline diet caused just a small jump in carrying capacity as shown in the posi-
tive control diet. It is important to bear in mind that all scenarios consistent with the Dietary Guidelines for
Americans are considered nutritionally sucient. From the standpoint of meeting human food needs, they
are all equivalent. us, dierences in carrying capacity should represent the trade-os of food preferences
rather than nutritional quality.
e absolute magnitude of the numbers is large. All estimates of carrying capacity exceed the size of the
2010 U.S. population by at least 30%. is result suggests that the U.S. has a large food security buer, which
it currently shares with other countries through trade. In addition, the dierences between the scenarios
suggest that the dietary changes could free up capacity to feed hundreds of millions of people around the
globe. To meet global food needs in 2050, a potential of this magnitude is signicant. Whether the windfall
of such dietary change could be redistributed to those in need remains an important unanswered question.
Nonetheless, this research suggests that U.S. agricultural land has the capacity to feed many more people
than reside in the U.S. and this margin might be extended through dietary change.
4.3 Caveats and lingering questions
While this study shows that dietary change has the potential to reduce requirements for agricultural land
and increase carrying capacity, the results are perhaps best treated as a foundation for further hypothesis
testing. Only one version of each diet scenario was run in the analysis. More work is needed to understand
the range of variability within each diet, and the sensitivity of results to changes in key parameters such as
crop yields and food waste. In particular, each of the diets is represented by a single set of food preferences,
and it is possible to envision variations on each diet that conform to the same structure in terms of food
group servings yet dier in terms of the constituent foods. For example, diets containing meat could vary in
terms of the proportion of servings from beef, pork, and poultry. Likewise, earlier work has shown that land
requirements can be inuenced by the amount of fat in the diet (Peters et al., 2007), and scenarios could
conform to the same food group distributions but vary in terms of the calories from added fats. Quantifying
the sensitivity of the model output to variability in input data is an important next step. Nonetheless, such
work seems likely to conrm that dietary choices are important.
In addition to variation within scenarios, future work should rene the most appropriate boundaries for
scenarios. is analysis examined multiple diets with reduced meat, since such a shift is consistent with recom-
mended nutritional advice. However, it may also be important to examine diets in which meat consumption
is greater than the baseline, since model projections of global food demand suggest that demand for livestock
products in OECD countries will continue to increase, albeit slowly (Valin et al., 2014). Similarly, complete
adoption of dietary guidelines by a population is highly unlikely, if not impossible, so comparison of diets that
reect a partial and imperfect transition towards healthier eating would be benecial. Finally, the modeling
of a population-wide ovolacto- or lacto-vegetarian diet leaves open the question of the fate of animals from
the dairy or egg-production systems that in the current agricultural system would be raised for meat (such as
dairy calves) or used as meat at the end of their productive life span (such as and culled dairy cows).
5. Conclusions
Dietary change has been proposed as part of a strategy to ensure future food security for a growing world
population while addressing environmental challenges associated with agricultural production. e ndings
of this study support the idea that dietary change towards plant-based diets has signicant potential to reduce
the agricultural land requirements of U.S. consumers and increase the carrying capacity of U.S. agricultural
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
Carrying capacity of U.S. agricultural land: Ten diet scenarios
13
resources. Future work is needed to determine the best way to share this productive bounty with the rest
of the world, but potential for dietary change to inuence land requirements and carrying capacity is clear.
Diet composition matters.
is study focuses attention on some underappreciated concerns. While agricultural land is often dis-
cussed in the aggregate, our analysis shows that accounting for the partitioning of land between grazing
land, cultivated cropland, and perennial cropland has a strong inuence on estimates of carrying capacity.
Indeed, we demonstrate that under a range of land use conditions, diets with low to modest amounts of meat
outperform a vegan diet, and vegetarian diets including dairy products performed best overall. Finally, the
analysis illustrates how carrying capacity can be used to measure the potential food output of agricultural land.
Moreover, the model presented herein provides a basis for exploring an even wider range of diet scenarios,
and to further examine which diets make most ecient use of available land.
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Carrying capacity of U.S. agricultural land: Ten diet scenarios
15
Contributions
Design of the US Foodprint model was led by CP.
Suggestions to model design were made by AD, TG, and JP.
Primary responsibility for collecting data to parameterize the model was born by AD and JP.
Design of the scenarios was led by CP with input from GF and JW, who worked with CP on an earlier version of
the model, and from TG, who worked on a related analysis of livestock feed requirements.
Writing of the manuscript and preparation of tables and gures was led by CP.
All co-authors (AD, GF, TG, JP, and JW) read and commented on the manuscript, making suggestions on how to
condense the narrative, clarify writing, frame the analysis, and interpret ndings.
Acknowledgments
We thank the editors and anonymous reviewers for the time and eort they invested in reading and critiquing the
original manuscript and for their insightful and constructive feedback.
Funding information
is research was supported in part by funding from the W.K. Kellogg Foundation, grant number P3008987.
Competing interests
e authors have no competing interests to declare.
Supplemental material
Table S1. Grazed forage yields on cropland pasture and other grazing lands (DOC)
doi: 10.12952/journal.elementa.s001
Table S2. Processing conversion parameter estimates obtained from non-standard sources (DOC)
doi: 10.12952/journal.elementa.000116.s002
Text S1. Data sources, assumptions, supporting calculations, and structure of the U.S. Foodprint model.
is supplemental material includes additional detail on certain calculations performed in the Methods and on the
structure of the U.S. Foodprint model. Text S1 is organized in three main sections, “Data sources and assumptions,”
“Supporting calculations,” and “Model structure.” e supporting calculations section includes ve subsections:
disaggregation of fats, processing conversions for dairy products, grazing yields, land use adjustments, and land
availability calculations. The model structure section describes the accompanying dataset.
doi: 10.12952/journal.elementa.000116.s003
Dataset S1. U.S. Foodprint model
e U.S. Foodprint Model is the spreadsheet model used to estimate the land requirements and carrying capacity
of all diet scenarios evaluated in the study.
doi: 10.12952/journal.elementa.000116.s004
Data accessibility statement
U.S. Foodprint Model: uploaded as supporting information as a self-contained spreadsheet (.xlsx le)
Copyright
© 2016 Peters et al. is is an open-access article distributed under the terms of the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Elementa: Science of the Anthropocene 4: 000116 doi: 10.12952/journal.elementa.000116
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