Vegetable Cost Metrics Show That Potatoes and Beans
Provide Most Nutrients Per Penny
Adam Drewnowski*, Colin D. Rehm
Center for Public Health Nutrition, School of Public Health, University of Washington, Seattle, Washington, United States of America
Vegetables are important sources of dietary fiber, vitamins and minerals in the diets of children. The United States
Department of Agriculture (USDA) National School Lunch Program has new requirements for weekly servings of
vegetable subgroups as well as beans and peas. This study estimated the cost impact of meeting the USDA
requirements using 2008 national prices for 98 vegetables, fresh, frozen, and canned. Food costs were calculated per
100 grams, per 100 calories, and per edible cup. Rank 6 score, a nutrient density measure was based on six nutrients:
dietary fiber; potassium; magnesium; and vitamins A, C, and K. Individual nutrient costs were measured as the
monetary cost of 10% daily value of each nutrient per cup equivalent. ANOVAs with post hoc tests showed that beans
and starchy vegetables, including white potatoes, were cheaper per 100 calories than were dark-green and deep-yellow
vegetables. Fresh, frozen, and canned vegetables had similar nutrient profiles and provided comparable nutritional
value. However, less than half (n=46) of the 98 vegetables listed by the USDA were were consumed .5 times by
children and adolescents in the 2003–4 National Health and Nutrition Examination Survey database. For the more
frequently consumed vegetables, potatoes and beans were the lowest-cost sources of potassium and fiber. These new
metrics of affordable nutrition can help food service and health professionals identify those vegetable subgroups in the
school lunch that provide the best nutritional value per penny.
Citation: Drewnowski A, Rehm CD (2013) Vegetable Cost Metrics Show That Potatoes and Beans Provide Most Nutrients Per Penny. PLoS ONE 8(5): e63277.
Editor: Harry Zhang, Old Dominion University, United States of America
Received December 10, 2012; Accepted April 1, 2013; Published May 15, 2013
Copyright: ? 2013 Drewnowski, Rehm. This 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.
Funding: This research supported in part by the US Potato Board. No additional external funding was received for this study. The funders had no role in study
design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: This research supported in part by the US Potato Board. No additional external funding was received for this study. This does not alter the
authors’ adherence to all the PLOS ONE policies on sharing data and materials.
* E-mail: email@example.com
The 2010 Dietary Guidelines for Americans (DGA)  have
emphasized how important vegetables are to a healthy diet. Eating
a wide variety of vegetables is a good way to improve dietary
nutrient density, without consuming excess calories . In the
United States Department of Agriculture’s (USDA) ChooseMy-
Plate application, half of the recommended plate is composed of
vegetables and fruit .
The National School Lunch Program has established weekly
requirements for total vegetables as well as for vegetable
subgroups: dark green, orange, starchy, and ‘‘other’’ vegetables
 as well as for beans and peas (legumes). Fresh, frozen, and
canned products are allowed to make up the 5-cup weekly total
. This recommendation, intended to capitalize on the nutrient
content of different vegetables, comes at a price since some
vegetables are significantly more expensive than others [4–6].
Furthermore, not all vegetables are equally accepted by school-
children . School food services would benefit from knowing
which vegetables are both acceptable and provide the most
nutrients per unit cost.
Vegetables are foods of high nutrient density and relatively low
energy content . The present research goal is to compare fresh,
frozen, and canned vegetables in terms of nutrients per calorie and
nutrients per penny. Our analyses, designed to follow the USDA
guidelines on school lunches , take into account the frequency
of consumption of different vegetables in the United States.
Ideally, vegetables served at school lunch ought to be nutrient-
dense, affordable, and appealing.
Providing healthier school meals without increasing costs poses
a challenge to school food services [8,9]. Meals built around
vegetables and fruit are nutrient-rich but tend to cost more per
calorie than do meals that are energy-dense but nutrient poor
[10,11]. There have also been concerns that some vegetables
simply do not provide sufficient calories, being 90% water .
How to measure vegetables prices has been another topic of
debate [12–14]. On one hand, food prices per gram do not reflect
the high water content of some vegetables and salad greens. On
the other hand, food prices per calorie mask the fact that some
vegetables are more nutrient-rich. Nutrition economics could
benefit from better tools . In the present analyses we developed
a new metric of nutrients per unit cost.
Measures of affordable nutrition should help identify those
vegetables that provide the best nutritional value per penny and
are well-accepted by schoolchildren . Previous studies have
shown that some vegetables can be low-cost sources of several
key nutrients [4,10], including potassium, fiber, and vitamin C.
In the present study, vegetables that provide the best nutritional
value at an affordable cost were identified using a combination
of nutrient profiling methods  and national food prices data
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The Nutrient and Food Price Databases
The nutrient composition database.
Nutrient Database for Dietary Studies 2.0 (FNDDS 2.0) is used to
code, process, and analyze the What We Eat in America food
intake data for 2003–4 . The files include detailed food
descriptions for .6,940 foods from all food groups, typical food
portions and weights, method of preparation (where available),
and nutrient values for energy and 60 nutrients. Each food is
identified by a unique 8-digit code, where the first digit identifies
the major food group. The second digit identifies subgroups (white
potatoes, dark green vegetables, deep yellow vegetables, tomatoes,
and other vegetables), whereas the third and subsequent digits
provide ever-finer discrimination down to the individual food item.
The FNDDS 2.0 database also specifies whether the vegetables
were consumed cooked or raw and whether they were cooked
from fresh, frozen or canned. Canned and bottled vegetable juices
and vegetable soups are included in the vegetables group. The
FNDDS 2.0 database generally does not provide brand names and
the vast majority of items in the vegetable group are generic .
This version of FNDDS was chosen because MyPyramid
Equivalents matching the database were available. Such data
were not available with newer versions of FNDDS, including those
that correspond to more recent National Health and Nutrition
Examination Survey (NHANES) cycles.
The food price database.
based on the 2011 Economic Research Service and USDA report
, which used 2008 Nielsen Homescan data to calculate the
average price of a pound (or, for juices, a pint) of 153 fresh and
processed fruits and vegetables at retail stores. In order to estimate
price per edible cup equivalent for each food, retail quantities were
adjusted for the removal of inedible parts and cooking that occur
prior to consumption . For example, 1 pound of store-bought
fresh pineapple yields 0.51 pound of edible pineapple. Data from
the USDA National Nutrient Database for Standard Reference
(Release 21) and USDA’s Food Yields Summarized by Different
Stages of Preparation were used to estimate edible weights. The
MyPyramid Equivalents Database, 2.0 was used to define edible
The 2008 USDA fruit and vegetables prices were merged with
the FNDDS 2.0 nutrient composition database. Food and Drug
Administration serving sizes were based on Reference Amounts
Customarily Consumed (RACC).
The USDA Food and
Fruit and vegetable prices were
The Rank 6 Affordability Index
The 2010 DGA identified vegetables as excellent sources of six
nutrients: dietary fiber; potassium; magnesium; and vitamins A, C
and K . For each of these nutrients, we estimated the % daily
value (% DV) provided per serving for each vegetable in the
database . This value can be used to identify the most nutrient-
rich sources of a single nutrient. An index-based measure was then
developed, based on the median ranking of the nutrient density of
these six nutrients, with a minimum possible score of 1 and a
maximum possible score of 98. This rank-based measure was then
divided by cost to create a new affordability measure, with higher
values representing greater ranking of these 6 target nutrients per
unit cost. Rankings were used as opposed to absolute values
because many vegetables contained no amount of any nutrients,
particularly for vitamin A.
Additional analyses graphically identified the foods providing
the most potassium and fiber. These nutrients were selected
because prior analyses suggested that they were nutrients most
sensitive to diet costs . In addition, they were identified by the
2010 Dietary Guidelines as nutrients of public health concern in
the American diet .
Frequency of Consumption
For maximum nutritional benefits, the vegetables that are
offered at school lunch by the food service ought to be accepted
and eaten by schoolchildren. For each of the 98 vegetables with
2008 prices provided by the USDA, we ascertained the frequency
of consumption (days 1 and 2) from food listings in the NHANES
2003–04 database among children and adolescents age 5–14, the
age groups most likely to participate in the school-lunch program.
Because some foods include many similar items in the NHANES
data, foods were combined (e.g., the nutrient database used in
NHANES 2003–04 includes 12 types of canned corn, so the sum
of frequency of consumption for these items were included). The
listed frequency of consumption was merely frequency of use and
did not reflect portion size. For example, raw tomatoes appeared
in the database 3,391 times, most likely as garnish, whereas tomato
juice appeared 38 times. However, the frequency measure does
indicate whether a given vegetable is a part of mainstream food
habits or not. In the present study, NHANES frequency of use was
a measure of presumed acceptance and availability.
Analyses were performed using the Statistical Package for the
Social Sciences (SPSS) version 11.0 and Stata 11.2. One-way
analyses of variance and comparisons between means (where
indicated) were the principal analyses performed. We evaluated
heteroskedacity graphically and with the Breusch-Pagan Test. If
there was evidence of heteroskedacity we estimated the robust
error variance using the method described by Davidson and
MacKinnon . An alpha-level of 0.05 was used to determine
Mean energy density, water content, and relative prices per
100 g, per 100 kcal, and per serving for 5 vegetable subgroups are
shown in Table 1. It can be seen that dark green vegetables
(including leafy greens) had the highest mean water content (91%)
and the lowest energy density. By contrast, beans and peas,
followed by starchy vegetables, had a lower water content and
higher energy density. The 5 USDA vegetable subgroups differed
in terms of energy density, water content, price per 100 g, per
100 kcal, and per edible cup (P,0.001).
The USDA vegetable subgroups also differed significantly in
terms of their nutrient density and nutrient cost (P,0.001). The
Rank 6 score of nutrient density and the Rank 6 score divided
by cost showed a significant main effect of USDA vegetable
subgroups. Although dark green vegtables had the highest
nutrient density scores, after accounting for cost, dark-green
vegetables (Rank 6 affordability score 112), starchy vegetables
(112) and beans (240) provided better nutritional value for
By contrast, fresh, frozen, and canned vegetables were not
significantly different from each other in cost, though there was
some indication of a difference by nutrient density, with raw
uncooked vegetables having significantly lower nutrient density
than fresh cooked vegetables. Fresh cooked, frozen and canned
vegetables were comparable in terms of nutrient density and no
differences were observed by the affordability metric for these
Vegetable Cost Metrics
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Table 1. Characteristics and prices of 98 items in the vegetable food group in the FNDDS 2.01nutrient composition database using ERS 20082prices.
# of times
Price per 100 g
Price per cup
Price per 100 kcal
Rank 6 Score3
School lunch subgroups
Red & orange vegetables
Beans & peas (legumes)
Vegetables, fresh, raw
Vegetables fresh, ckd
Total vegetables & beans
*Indicates robust test was used, as some evidence of heteroskedascity was present (p,0.10 Breusch-Pagan test for heteroskedasticity). Data are means and standard deviations by United States Department of Agriculture (USDA)
lunch regulation subgroup.
1USDA Food and Nutrient Database for Dietary Studies 2.0.
2Economic Research Service.
3Higher scores indicative of higher nutrient density.
4Higher values represent greater amounts of 6 target nutrients per cost.
5Data for beans and peas are not repeated here.
6P-value of difference for each outcome does not include beans or peas and is based on a sample size of 86 foods.
Vegetable Cost Metrics
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Frequency of Consumption
Data in Table 1 show that the relative frequency of
consumption varied widely across vegetable subgroups. The
USDA vegetable prices database included 98 whole vegetables,
of which 81 were consumed at least once, and 46 were consumed
at least 5 times, while 17 were not consumed by any children and
adolescents, including frozen mustard greens, canned kale, fresh
cooked kale, canned turnip greens, frozen turnip greens, canned
mustard greens, frozen winter squash, canned lima beans, canned
potatoes, canned okra, frozen artichoke, canned summer squash,
fresh artichoke, fresh cooked brussels sprouts, canned whole
mushroom slices, frozen okra and canned artichoke.
The most frequently consumed vegetables were French fried
potatoes, iceberg lettuce, and raw tomatoes. Once the acceptance
criterion was applied, the number of dark green and red and
orange vegetables on the USDA list dropped from 30 to 12,
whereas the number of ‘‘other’’ vegetables dropped from 46 to 21.
To make the present analyses directly applicable to the school
lunch situation, further analyses were restricted to those vegetables
that were consumed .5 times in the NHANES database. Those
46 vegetables, divided into USDA school lunch vegetable
subgroups, are presented in Table 2, together with their
frequencies of consumption.
Lowest Nutrient Costs Per Penny
Figure 1 provides a graphic representation of the monetary
costs of obtaining 10% DV of fiber (x-axis) and potassium (y-axis)
from individual vegetables and from beans and peas. Items closest
to the origin are those that provide these nutrients at the lowest
cost. It can be seen that the lowest-cost items were beans (pinto
beans and lentils), white potatoes, sweet potatoes, French fried
potatoes, and carrots. Of these, beans were least expensive but also
provided the most calories per gram.
Table 2 identifies the median price per 10% DV for the 6
nutrients of interest by the USDA school lunch vegetable category.
Because of the differences identified in Figure 1, starchy
vegetables are presented overall and are further disaggregated to
include potatoes and non-potatoes. The median cost per 10% DV
for potassium and fiber was lowest for potatoes ($0.14 for
potassium and $0.19 for fiber) and beans ($0.10 and $0.05). For
vitamin C, potatoes ($0.10) and dark-green vegetables ($0.12) had
the lowest cost per 10% DV. For vitamin A and K, dark-green
vegetables had the lowest cost per 10% DV. The combined
affordability metric showed that beans had the highest median
value (257.5), followed by potatoes (177.9). Individual vegetables,
including white potatoes, and different varieties of beans that were
the lowest-cost sources of specific nutrients are further identified in
Figure 2 ranks the 46 acceptable vegetables according to the
composite Rank 6 affordability index. Overall, the best nutritional
value was provided by beans, white potatoes, sweet potatoes, and
carrots. Of the vegetables with the highest affordability scores,
white potatoes (fried and non-fried) and carrots had the highest
frequency of use. It is also worth noting that not all of the top-
ranked products were fresh; frozen and canned produce also
benefited from high affordability scores, specifically canned beans,
green beans and collard greens.
To manage nutrition and costs, vegetables served as part of the
school lunch ought to be nutrient dense, affordable, easy to
prepare and serve, and appealing to children. The present analyses
combined nutrient density, cost, and frequency of use to create
new affordability metrics. Vegetables provide some key vitamins
and minerals at a relatively low cost, as described in prior research
Nutrient density measures were based on 6 nutrients. Based on
Dietary Guidelines to Americans, vegetables are important sources
of fiber, potassium, magnesium, and vitamins A, C, and K in the
American diet. The Rank 6 affordability index incorporated a
rank-based measure of nutrient density and the cost per standard
serving to provide a summary measure of affordability. The
individual monetary cost of 10% DV for each of these 6 nutrients
was another measure of nutrient cost.
Finally, frequency of use in the 2003–4 NHANES database was
the population based indication of a given vegetable’s acceptabil-
Table 2. Median price ($) per 10% Daily Value (DV) by school lunch vegetable category.
Vegetable subgroupN Potassium Dietary fiber MagnesiumVitamin CVitamin A Vitamin KRank 6 Score Rank 6/Cost
Starchy – all4,5
Starchy - Potatoes4
Starchy - excludes potatoes5
Analysis restricted to vegetables and beans listed 5 or more times in 2003–4 NHANES1database.
1National Health and Nutrition Examination Survey.
2Broccoli florets, fresh, cooked (41); Broccoli, frozen (41); Spinach, fresh-cut, fresh, raw (40); Romaine lettuce, fresh (19); Collard greens, frozen (8); Spinach, frozen (7).
3Carrots, baby, fresh, raw (138); Carrots, whole, fresh, raw (138); Carrots, frozen (20); Sweet potatoes, fresh, cooked (12); Sweet potato fries, frozen (5);
4Potatoes, frozen, French fries (838); Potatoes, fresh, cooked (79).
5Corn, sweet, whole kernel, canned (104); Corn, sweet, whole kernel, frozen (104); Peas, green, frozen (29); Corn, sweet, fresh, cooked (23); Peas, green, canned (7).
6Pinto beans, dried (65.5); Pinto beans, canned (65.5); Black beans, dried (16.5); Black beans, canned (16.5); Lentils, dried (14); Red Kidney beans, canned (11); Red kidney
beans, dried (11).
7Iceberg lettuce, fresh, raw (708); Tomatoes, cherry, fresh, raw (151); Tomatoes, roma, fresh, raw (151); Tomatoes, round, fresh, raw (151); onions, fresh, raw (146);
Cabbage, fresh, cooked (54); Green beans, whole, frozen (40); Green beans, cut, frozen (40); Green beans, cut, canned (31); Avocados, fresh, raw (31); Green beans, whole,
canned (31); Brussels sprouts, frozen (23); Celery stalks, fresh, raw (22); Celery hearts, fresh, raw (22); Green peppers, bell, fresh (20); Radishes, fresh, raw (13); Red
peppers, bell, fresh (12); Olives, black, pitted, canned (11); Asparagus, fresh, cooked (11); Tomatoes, canned (6); Squash, summer, frozen (5).
Vegetable Cost Metrics
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Figure 1. The relative cost for 10% Daily Value for potassium and fiber, including frequency of consumption. Size of circle corresponds
to frequency of consumption by children and adolescents, age 5–14.
Table 3. Median and mean price per 10% Daily Value (DV) of single nutrients among vegetables consumed 5 or more times.
Median price per
Mean price per
10% DVFive lowest-cost options (cost per 10% DV)
Dietary fiber 460.310.43
Lentils, dried ($0.03); Pinto beans, dried ($0.04); Red kidney beans, dried ($0.04); Black beans,
dried ($0.05); Red Kidney beans, canned ($0.08)
Potassium 46 0.531.23
Lentils, dried ($0.08); Pinto beans, dried ($0.08); Potatoes, fresh, cooked ($0.08); Black beans,
dried ($0.09); Red kidney beans, dried ($0.10)
Pinto beans, dried ($0.06); Black beans, dried ($0.08); Lentils, dried ($0.09); Red kidney beans,
dried ($0.10); Potatoes, fresh, cooked ($0.17)
Vitamin A 361.61 3.09
Carrots, whole, fresh, raw ($0.04); Sweet potatoes, fresh, cooked ($0.04); Carrots, frozen
($0.05); Carrots, baby, fresh, raw ($0.06); Collard greens, frozen ($0.08)
Vitamin C 440.28 0.43
Red peppers, bell, fresh ($0.03); Broccoli florets, fresh, cooked ($0.04); Green peppers, bell,
fresh ($0.04); Broccoli, frozen ($0.05);
Cabbage, fresh, cooked ($0.05)
Vitamin K 452.93 10.29
Collard greens, frozen ($0.04); Spinach, frozen ($0.08); Spinach, fresh-cut, fresh, raw ($0.14);
Brussels sprouts, frozen ($0.17);
Romaine lettuce, fresh ($0.19)
Vegetable Cost Metrics
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ity. Out of 98 vegetables, only 46 were consumed more than 5
times, led by potatoes, carrots, tomatoes, onion and iceberg
lettuce. Clearly, not all vegetables were the same in terms of
general appeal and some were more likely than others to be
rejected by schoolchildren.
Previous research, based on 2003 national food prices per
calorie, per serving, and per gram [10,13] showed that vegetables
were low-cost sources of potassium, vitamin A, vitamin C, and
dietary fiber. Lowest-cost fiber was provided by beans and legumes
whereas lowest-cost vitamin C was provided by vegetables and
fruit [10,13]. The present study used the most recent USDA
vegetable prices for 2008  and followed the recent school
lunch regulations to classify vegetables into subgroups.
Improved school lunches need to maximize nutrition and
minimize waste while remaining cost neutral . The present
potatoes, beans, carrots and some dark green vegetables as
both affordable and nutrient-dense. However, not all affordable
nutrient dense vegetables are part of mainstream eating habits.
The consumption frequency of sweet potatoes and some dark
green leafy, and non leafy vegetables was low. Only beans,
white potatoes and carrots managed to combine nutrient
density, affordability and consumer acceptance. White potatoes
rivaled beans in nutrient density and had lower energy density
and much higher frequency of use.
Additional and more detailed studies are clearly needed to
determine which affordable nutrient-rich vegetables, fresh, frozen,
canned or processed are best accepted by school children. For
example, there may be standouts among the dark green vegetables
and yellow/orange vegetables that combine high nutrient density
and excellent value for money. Also, as indicated in Figure 2,
high nutrient affordability scores were not limited to fresh or raw
produce but included vegetables that were frozen and canned.
While countless studies have evaluated nutrient density scores to
date [21–24], few studies have attempted to combine measures of
affordability and nutrient density into a single summary score .
To date, the focus has been on evaluations of the affordability of
single nutrients [26,27] or the ratio of a nutrient density and
affordability measure (unpublished data). The Affordable Nutri-
tion Index (ANI) is one proposed measure, which is the ratio of the
Nutrient Rich Fodos index per standard portion and the cost per
standard portion, with higher values reflecting greater nutrient
density per cost. The nutrient density affordability measure used
here follows a similar approach and is highly correlated with the
ANI (r=0.94). The measure used here is unique in that it is was
specifically created to evaluate the nutrient density and afford-
ability of a single food group, whereas the ANI may have greater
utility for between food-group comparisons.
This study has some limitations worth noting. First, it is
important to note that the prices used here represent the prices
Figure 2. Rank 6– Nutrient Density Score among vegetables consumed 5 or more times.
Vegetable Cost Metrics
PLOS ONE | www.plosone.org6 May 2013 | Volume 8 | Issue 5 | e63277
experiences by a relatively small number of Americans, and may Download full-text
not reflect those prices actually experienced by consumers or
schools, or those in specific regions that may have higher/lower
costs . Schools may be able to purchase items for less cost due
to volume. However, assuming that bulk purchasing discounts do
not vary considerably by vegetable type, the results of this study
The nutrient density and affordability index used here has some
additional limitations. First, the use of a rank-based score assumes
that the difference between each subsequent ranking is similar.
However, the use of a rank-based score does avoid the problem of
extreme values having undue influence on the summary score.
Other nutrient density measures are similarly unit-free [21–24].
Second, the examination of affordability and nutrient density is
dependent on the nutrients used to calculate the nutrient density
score. Therefore, results may vary if different nutrients are used.
The nutrients used here were specifically identified in the 2010
Dietary Guidelines as important nutrients for vegetables. Lastly,
the nutrient density score used here focuses solely on nutrients to
encourage, and does not account for fat, sugar or sodium. Both
cooked and raw vegetables are often served with added fat and
salt. In addition, care should be taken in examining the nutrient
affordability of fried products which are more likely to contain
added fats and sodium. However, these products are most
frequently consumed by children, making their inclusion in this
analysis justified. In comparison to previous work, this study only
evaluated the affordability within a single food group. Therefore
the results of this study can only be used to evaluate the vegetable
group, and cannot evaluate the potential place of other food
groups, such as fruit, grains, or dairy products, which may be
important in the evaluation of potassium, fiber and magnesium.
School lunches need to balance taste, cost, convenience and
nutritional value [28,29]. Hungry children may opt for foods of
high energy density but potentially lower nutritional value. The
present calculations, thus far limited to vegetables, illustrate how
the econometric approach to nutrient profiling can help identify
affordable nutrient-rich foods within each food group. Effective
menu planning requires knowledge of federal regulations,
nutrient density standards in relation to costs and children’s
food preferences. Joining nutrient density profiling with the
economics of food choice behavior is a relatively novel area of
Conceived and designed the experiments: AD CDR. Performed the
experiments: AD CDR. Analyzed the data: AD CDR. Contributed
reagents/materials/analysis tools: AD CDR. Wrote the paper: AD CDR.
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PLOS ONE | www.plosone.org7 May 2013 | Volume 8 | Issue 5 | e63277