40:60: The optimal ratio between animal and plant-based proteins for health and environment

Abstract

There is currently little agreement on the optimal ratio of animal-sourced (ASP) versus plant-sourced proteins (PSP) in sustainable human diets. We deployed a biophysical optimization model to find the optimal ASP:PSP ratio at current and recommended protein intake levels for the EU28 countries. Results show that the lowest environmental impact for both land use and greenhouse gas emissions is achieved at a recommended protein intake of 46 g protein/cap/day with an ASP:PSP ratio of 40:60 (18 g ASP/cap/day). At current protein intake (82 g protein/cap/day), the optimal ASP:PSP ratio for land use ranges evenly between 22:78 and 60:40 (18 and 49 g ASP/cap/day) while for greenhouse gas emissions the optimal ASP:PSP ratio is at 40:60 (18 g ASP/cap/day). Diets containing less than 18 g ASP/cap/day show micronutrient inadequacies, leading to increases in both land use and greenhouse gas emissions.

Full text

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40:60: The optimal ratio between animal and plant-
based proteins for health and environment
Renske Hijbeek
Plant Production Systems Group, Wageningen University https://orcid.org/0000-0001-8214-9121
Anita Frehner
Research Institute of Organic Agriculture FiBL https://orcid.org/0000-0002-0039-8421
Renee Cardinaals
Wageningen University and Research
Elise Talsma
Wageningen University & Research https://orcid.org/0000-0002-6034-4708
Hannah Van Zanten
Wageningen University and Research https://orcid.org/0000-0002-5262-5518
Wolfram Simon (  wolfram.simon@wur.nl )
Wageningen University and Research (WUR) https://orcid.org/0000-0002-4324-4481
Article
Keywords:
Posted Date: June 5th, 2023
DOI: https://doi.org/10.21203/rs.3.rs-2885934/v1
License:   This work is licensed under a Creative Commons Attribution 4.0 International License. 
Read Full License

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Abstract
There is currently little agreement on the optimal ratio of animal-sourced (ASP) versus plant-sourced
proteins (PSP) in sustainable human diets. We deployed a biophysical optimization model to nd the
optimal ASP:PSP ratio at current and recommended protein intake levels for the EU28 countries. Results
show that the lowest environmental impact for both land use and greenhouse gas emissions is achieved
at a recommended protein intake of 46 g protein/cap/day with an ASP:PSP ratio of 40:60 (18 g
ASP/cap/day). At current protein intake (82 g protein/cap/day), the optimal ASP:PSP ratio for land use
ranges evenly between 22:78 and 60:40 (18 and 49 g ASP/cap/day) while for greenhouse gas emissions
the optimal ASP:PSP ratio is at 40:60 (18 g ASP/cap/day). Diets containing less than 18 g ASP/cap/day
show micronutrient inadequacies, leading to increases in both land use and greenhouse gas emissions.
Introduction
In recent years, the European Union (EU) has shown increasing interest in the transformation of the
current food system. With the European Green Deal and the embedded Farm to Fork Strategy, the EU
strives to be the world’s rst climate-neutral trade union1. To achieve this ambition, production and
consumption changes are needed which implies a radical food system redesign2.
One strategy that claims to respect both human and planetary health is to reduce the share of animal
sourced-foods in the human diet3. For instance, the scientic advisory organ of the Dutch Parliament has
initiated an investigation on the optimal ratio of animal products in diets, and Germany has launched a
far-reaching ‘Protein Crop Strategy’ (‘Beans, Peas & Co’) for promoting legume cultivation4,5. The incentive
for this so-called ‘protein transition’ relates to the fact that the livestock sector has a large impact on the
environment. The European sector contributes to 78% of terrestrial biodiversity loss, 81% of agricultural
GHG emissions, and uses around 65% of total agricultural land6 leading to feed-food competition
between animals and humans7. Nevertheless, animals are an important source of protein − 60% of all
protein are derived from animals. At the same time, the EU is facing a challenge regarding
overconsumption and diet-related diseases. Today’s protein intake levels are around 82 g protein/cap/day
(49 g animal protein and 33 g plant protein)8, while the European Food Safety Authority (EFSA) sets an
average requirement (AR) intake of 46 g protein/cap/day9. Moreover, the high consumption of processed
meat and red meat is associated with an increased risk of heart disease, certain types of cancer, and
diabetes type 210–12.
Although the impact of animal products on both the environment and human health is evident, there is no
consensus on the optimal dietary share of animal-sourced proteins (ASP) versus plant-sourced proteins
(PSP). Some studies suggest that eating a fully plant-based diet is the most sustainable13,14, while others
report that animals still play a crucial role and provide up to 30 g ASP/cap/day if used as waste stream
recyclers15–20. In the latter scenario, animals are only fed with products that humans cannot or do not
want to eat, enabling more ecient use of resources.

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The aim of this study was to assess the optimal ratio between ASP:PSP for human and planetary health
under two paradigms: one in which diets shift towards healthier eating patterns while maintaining current
protein intake, and a second where current protein intake is reduced to a healthy recommended protein
intake within the EU context. In both paradigms we looked for the optimal ratio that would either minimize
the amount of greenhouse gas emissions (GHG) emitted or total agricultural land use in the EU28 food
system. Results show that the lowest impact for both land use and GHG emissions is achieved when
protein intake levels are reduced to a recommended protein intake of 46 g protein/person/day with an
ASP:PSP ratio of 40:60 and 18 g ASP/cap/day.
Results
Scenarios
We used the Circular Food Systems optimization model (CiFoS), a biophysical optimization model, to
assess the optimal ASP:PSP ratio21. We assessed different scenarios to discover the optimal ASP to PSP
ratios which would minimize GHG emissions and/or land use. The ASP:PSP ratios were assessed under
two different paradigms: one in which diets shift towards healthier eating patterns while maintaining the
current protein intake of 82 g protein/cap/day and a second representing a healthy diet based on a
recommended protein intake of 46 g protein/cap/day. Healthy diets were dened by adhering to EFSA
nutrient requirements9 and recommended range of intake levels per food group derived from the EAT-
Lancet guideline22. ASP:PSP ratios started at current levels (60:40) - the reference level - and were
reduced in steps of 20% towards a fully plant-based diet while minimizing nutrient deciencies. We
assessed a total of 18 scenarios plus the reference scenario (Table1). The reference scenario matches
empirical data related to the current food system, (e.g., current crop production systems for domestic use
and export with associated areas) while minimizing the difference with the current food supply8,23,24
(objective function).

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Table 1
Protein levels per protein transition scenarios. LU = land use, GHG = greenhouse gas, Cur = current intake,
Rec = recommended intake, PI = protein intake, ASP = animal-sourced protein, PSP = plant-sourced protein,
cap = capita.
Scenario names Protein intake level ASP:PSP
ratio PI
(g/cap/day) ASP intake
(g/cap/day)
LU or
GHG_Reference_60:40 Current protein intake 60:40 82 49
LU or
GHG_CurPI_60:40 Current protein intake 60:40 82 49
LU or
GHG_CurPI_40:60 Current protein intake 40:60 82 33
LU or
GHG_CurPI_22:78 Current protein intake 22:78 82 18
LU or
GHG_CurPI_20:80 Current protein intake 20:80 82 16
LU or
GHG_CurPI_00:100 Current protein intake 00:100 82 0
LU or
GHG_RecPI_60:40 Recommended protein
intake 60:40 46 28
LU or
GHG_RecPI_40:60 Recommended protein
intake 40:60 46 18
LU or
GHG_RecPI_20:80 Recommended protein
intake 20:80 46 9
LU or
GHG_RecPI_00:100 Recommended protein
intake 00:100 46 0

The impact of ASP:PSP ratios on land use and GHG emissions
Our results show three remarkable ndings. First, the largest reduction in land use (41%) and GHG
emissions (61%) was achieved solely by applying circularity principles (see methods). The ASP:PSP ratio
remained unchanged – 60:40 ASP:PSP (Fig.1a,b). Secondly, applying circularity principles plus shifting
the ASP:PSP towards more PSP reduces GHG emission by 80% (Fig.1c,d) while land use is not
remarkably impacted by changes in ASP:PSP ratios (Fig.1a,b). Thirdly, a fully plant-based diet resulted in
nutrient inadequacies with increased environmental impacts (Fig.1a-d).
Finding 1: potential of applying circularity principles
Using circularity principles, land use can be reduced annually by 41% (from 172 to 101 mil ha) and GHG
emissions by 61% (from 1172 to 455 kg CO2eq/cap/year) at current protein intake levels and the current
60:40 ASP:PSP ratio (paradigm 1) (Fig.1a,c). This reduction is due to improved use of waste streams

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(e.g., as animal feed) and optimized plant and animal production systems. An even larger reduction of
land use and GHG emissions can be achieved by applying production-side circularity principles as well as
by reducing protein intake to recommended levels while maintaining the ASP:PSP at 60:40 (paradigm 2).
At recommended protein intake, land use was reduced by 79% (from 172 to 36 mil ha) while GHG
emissions decreased by 85% (from 1172 to 237 kgCO2eq/cap/year) (Fig.1b,d).
Finding 2: optimal ASP:PSP ratio
Land use remains constant under different ASP:PSP ratios. The largest reduction in land use under the
current protein intake paradigm, was achieved with a current ASP:PSP ratio of 60:40 (49 g ASP/cap/day):
41% reduction in land use (71 mil ha). Changing the ASP:PSP ratio to 40:60 (33 g ASP/cap/day) or 22:78
(18 g ASP/cap/day) reduced land use with 39% (67 mil ha) and 36% (63 mil ha), respectively. Thus land
use only increases with 8 mil ha (5%) when shifting from 60:40 to 22:78. When transitioning towards
healthy protein intakes (paradigm 2) land use was reduced by 80% to 35 mil ha. The 40:60 ratio (18 g
ASP/cap/day) reveals similar results to that of the 60:40 ratio (28 g ASP/cap/day) with a reduction in
land use of 79% to 36 mil ha. Changing the ASP:PSP ratio is therefore not an appropriate indicator for
land use reductions. However, protein intake is; lowering protein intake from 82 to 46 g/cap/day reduces
land use by 74 mil ha.
For GHG emissions the largest reduction under both paradigms (current and recommended protein intake
levels) were achieved with an ASP:PSP ratio of 40:60 (33 g ASP/cap/day paradigm 1 and 18 g
ASP/cap/day paradigm 2). GHG emission are reduced by 76% to 281 kgCO2eq/cap/year under the rst
paradigm and by 85% to 171 kgCO2eq/cap/year under the second paradigm. Reducing ASP:PSP ratios in
our diets thus has a greater effect on GHG emissions than on land use due to the strong link between
GHG emissions and farmed animals – especially ruminants - in the food system.
Finding 3: nutrient inadequacy and increased land use and GHG emissions in fully-plant-based diets
Nutrient inadequacy emerged consistently below a daily intake of 18g ASP/cap/day. Decreasing ASP
further not only led to increased nutrient inadequacy but also to increased land use and GHG emissions.
This is due to an increased demand for crops high in certain nutrients (e.g., calcium), such as legumes,
vegetables, nuts and seeds, and fruits, to compensate for the absence of animal-sourced nutrients. The
increased use of articial fertilizers required for these crops and transportation of foods also results in
higher GHG emissions. The main nutrients leading to inadequacies were vitamin B12, EPA and DHA
(inadequately supplied below 18 g ASP/cap and day) as well as calcium, selenium, vitamin B3 and
energy (at the border to nutrient inadequacy) (Fig.3).
Food system redesigns at optimal ASP:PSP ratios
Transitioning the food system towards optimal ASP:PSP ratios requires a redesign of the food system in
terms of diet, crop production systems, and animal production systems.
Dietary strategies to reduce land use and GHG emissions

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Vegetables are the only food group for which consumption increased in all scenarios in order to shift to
healthier diets. Their contribution to total protein intake is however limited (6–8 g/cap/day). In terms of
overall supply, dairy (13 g – 19 g) and grains (8 g – 20 g) are the main protein suppliers in all scenarios.
However, some notable differences were observed depending on the scenario.
At current protein intake levels (paradigm 1), the reduction in land use and GHG emissions is mainly due
to a shift in protein sources. Fish consumption largely increased and therefore seems to be a strategy to
reduce both land use and GHG emissions when protein intake levels remain high. The consumption of red
meat (-73% to -79%), eggs (-73% to -100%) and dairy (-10% to -38%) were reduced while chicken meat
increased (up to 12%) when decreasing land use and decreased (-100%) when minimizing GHG
emissions. Moreover, to further minimize GHG emissions, legumes are favoured over chicken, and
legumes proteins are largely increased to 29 g of protein per cap per day.
At recommended protein intake levels (paradigm 2), ASP was reduced to 18 g (ASP:PSP ratio of 40:60)
when reducing land use and GHG emissions, mainly from dairy (13g) and grains (13g-16g). Lowering the
overall protein intake to recommended intake levels increased the risk of nutrient inadequacies. At an
ASP:PSP ratio of 40:60, calcium, vitamin B12 and energy are going towards nutrient inadequacy, driving
the model to increase food sources with higher amounts of these scarce nutrients (Fig.3). Nutritious nuts
and seeds and fruits were therefore selected as nutrient sources (Table2).

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Table 2
Amount of protein sourced per food group for the optimal ASP:PSP ratio when minimizing land use and
GHG emissions and the FAO reference. The percentage shows the relative increase (+) or decrease (-)
when comparing the optimal scenarios to the FAO reference scenario. LU = land use, GHG = Greenhouse
gas emissions, Cur = current protein intake, Rec = Recommended protein intake, cap = capita.
Food
group FAO
Reference
(g/cap/day)
LU_Cur_60:40 LU_Rec_40:60 GHG_Cur_40:60 GHG_Rec_40:60
Red meat 19 5 (-73%) 4 (-79%) 4 (-79%) 4 (-79%)
Chicken 11 12 (12%) 0 (-100%) 0 (-100%) 0 (-100%)
Fish 6 14 (136%) 1 (-83%) 9 (52%) 1 (-83%)
Dairy 21 17 (-20%) 13 (-38%) 19 (-10%) 13 (-38%)
Eggs 4 1 (-73%) 0 (-100%) 1 (-73%) 0 (-100%)
Oil Fat 1 0 (-100%) 0 (-100%) 0 (-100%) 0 (-100%)
Legumes 4 4 (14%) 0 (-100%) 29 (725%) 4 (14%)
Nuts seeds 2 0 (-100%) 3 (97%) 3 (97%) 2 (31%)
Vegetables 4 6 (67%) 6 (67%) 8 (123%) 6 (67%)
Fruits 1 1 (-30%) 2 (39%) 1 (-30%) 1 (-30%)
Tubers 3 2 (-29%) 1 (-65%) 1 (-65%) 2 (-29%)
Grains 29 20 (-32%) 16 (-46%) 8 (-73%) 13 (-56%)
Sugars 0 0 (-100%) 0 (-100%) 0 (-100%) 0 (-100%)

Strategies for reducing land use and GHG emissions by changing crop production systems
One key factor to reduce land use and GHG emissions in all scenarios was to increase the production of
legumes, especially soybeans. This is due to their high protein content (up to 20 g protein/100g and 36 g
protein/100g for soybeans), their favourable amino acid prole (especially for soybeans), and the ability
of legume crops to x atmospheric nitrogen, thereby reducing the amount of articial fertilizer required
and associated GHG emissions. At current protein intake levels (paradigm 1) the relative land share of
legumes to all other crops increased by a factor of 13 (to 40 mil ha of the 101 mil ha), to cover almost
half of the arable land when reducing land use and a factor of 16 (to 59 mil ha of the 122 mil ha) when
reducing GHG emissions (Fig.2 and S1). Although at recommended protein intake level (paradigm 2),
cereals were favoured over legumes, the production of legumes still increased 5 times (to 40 mil ha of the
36 mil ha) when reducing land use, and 11 times (to 59 mil ha of the 122 mil ha) when reducing GHG
emissions. In addition to the increase in legumes, vegetable and oil crops also increased considerably
under both paradigms, while forage crops and permanent grassland decreased in land share.

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Strategies for reducing land use and GHG emissions by changing animal production systems
Overall animal numbers are largely reduced. Nevertheless, the reduction in animal numbers is larger when
reducing GHG emissions compared to land use. Fish is the only animal production system where
numbers increased; this can be explained by three factors: rst, fatty sh are the most important provider
of omega-3 fatty acids (i.e., alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), docosahexaenoic
acid (DHA)), a nutrient causing nutrient inadequacy. Second, sh have an ecient protein conversion
ratio; compared to other animal production systems, they need less nutrients to produce proteins for
human consumption25. Last, sh production - especially offshore salmon – does not require agricultural
land as long as no additional feed has to be grown, making it the most land ecient animal type when
minimizing land use. In addition to an increase in sh in paradigm 1, broiler meat also increased (current
protein intake) while land use was reduced. Similar to sh, broilers have an ecient protein conversion
factor. In this scenario, broilers were mainly fed with food system leftovers thereby reducing land use. All
other animal production systems were largely reduced: beef (-3% to -100%), pigs (-69% to -100%), layers
(-66% to -100%) and dairy (-66% to -100%) compared to the reference scenario (Figure S2). Although dairy
numbers decreased, dairy in general is clearly favoured over other animal production systems as it
provides highly nutritious food (i.e., milk and meat) while at the same time upcycling human-inedible
biomass like grass.
Transportation strategies to reduce emissions
Our results show that a highly effective strategy to reduce GHG emissions is cutting down on
transportation. In the optimal GHG minimizing scenarios, the share of transportation to the whole GHG
emissions was only 10%, compared to 29% in the reference scenario. However, transitioning towards a
fully plant-based diet in the food system leads to an accompanying increase in transportation emissions,
since the acquisition of location-specic and nutrient-rich crops exclusively cultivated in certain areas of
the EU28 necessitates sourcing food items from more distant regions. This shows the clear trade-off
between reducing land use and greenhouse gas (GHG) emissions regarding transportation emissions
(Figure S3).
Discussion
The optimal ASP:PSP ratio: 40:60
Transitioning towards healthy diets with recommended protein intake levels results in the lowest land use
(80% reduction) and GHG emission (85% reduction) with an ASP:PSP ratio of 40:60. When shifting
towards healthier diets while maintaining current protein intake, the optimal ASP:PSP ratio for land use
ranges between 22:78 and 60:40 (36% − 41% reduction), while for greenhouse gas emissions the optimal
ASP:PSP ratio is 40:60 (76% reduction).
Overconsumption of proteins therefore has a large environmental impact, especially on land use. We
found a difference of 66 mil ha between the optimal land use scenarios of current vs recommended

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protein intake. This nding aligns with previous studies showing the impact of overconsumption on the
environment26. It should however be noted that our results show that a reduction of protein towards
recommended protein intake levels increases the probability for nutritional inadequacies, as more
nutrients move towards the lower end of requirements. Moreover, although requirements for individual
amino acids had to be met, we did not consider protein quality and digestibility. Including these aspects
may affect the results as the fraction of total protein taken up by the body will be lower in plant-based
diets. This may imply that the protein recommendation should be higher than used in this study.
Nevertheless, the EFSA protein recommendations are based on a mixed EU diet and therefore already
assume a certain share of protein from plant-sources9. Careful planning is needed to ensure the intake of
both macronutrients and micronutrients remains adequate. From that perspective, a protein intake above
the average requirement can help avoid nutrient inadequacies if the share of PSP in EU diets is increased.
The potential of applying circularity principles
Although an ASP:PSP ratio of 40:60 results in the lowest land use and GHG emissions, our results show
that a large reduction can be achieved when solely applying circularity principles and without changing
the ASP:PSP ratio. Land use can be reduced by 41% and GHG emissions by 61% without changing total
protein intake or share of animal-sourced protein. The circularity principles were i) feeding animals with
products human cannot or do not want to eat17, ii) increasing the edible ratio of animals, i.e., all edible
parts of farmed animals are consumed by humans and, iii) improving nutrient re-cycling by fostering
circular fertilization using leguminous crops in crop rotation, compost from organic waste streams,
manure, and crop residues. Our ndings support recent studies showing that agricultural land can largely
be spared for other purposes when feeding farmed animals with human-inedible products, and reducing
animal numbers accordingly28. This spared land could then be used for other purposes, for example to
sequester carbon through forests, increase biodiversity or to produce biofuels29.
Eliminating nutritional inadequacy in plant-based diets
We show that, when shifting towards plant-based diets, we need to balance both micronutrients and
macronutrients to ensure nutritionally adequate diets. When transitioning to a plant-based diet, a suite of
(predominantly animal-sourced) micronutrients such as vitamin B12, calcium, EPA and DHA drive GHG
emissions and land use30,31. It is therefore relevant to understand whether these nutrient inadequacies
can be mitigated with future foods or fortied food products like seaweeds, insects and cultured meat to
substitute animal-sourced micronutrients in plant-based diets32–35 while providing an environmentally
friendly solution36,37. Other studies report that future food diets in the EU can reduce land use (-87%) and
GHG emissions (-83%) compared to current production systems36,38.37 found that food-based strategies
like fortication, biofortication and dietary diversication can improve micronutrient intake. Thus,
adding future foods and food fortication to our suite of dietary options can have a benecial effect on
land use and GHG emissions when transitioning towards more plant-based diets, yet these were not
included in this study39,40.

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No regret solutions
Food system redesigns are complex and, as our results reveal, both trade-offs and synergies occur
between minimizing land use and GHG emissions. So-called no regret solutions (synergies) to reduce
both land use and GHG emissions were: i) reduce the amount of ASP in diets by at least 20% to a ratio of
40:60 ASP:PSP, ii) increasing the cultivation of legumes to at least 40% of agricultural land, iii) increasing
cultivation of vegetables, increasing sh production and to largely reducing livestock numbers.
An example of a trade-off is the cultivation of legumes (> 40% of agricultural land) to reduce GHG
emissions. Legumes require more land for the same amount of protein compared to cereals but decrease
GHG emissions. This trade-off could be reduced by increasing legume competitiveness with novel
breeding strategies. Our results also reveal a trade-off related to transportation (land use increases with
local production due to decreased yields) which could be overcome when transitioning towards more
sustainable energy sources.
ASP:PSP ratio in food-based dietary guidelines (FBDGs)
We show that optimal ASP:PSP ratios depend on the total protein intake level. In high income-countries
with high protein intake, lower ASP:PSP ratios have large environmental and, in combination with a
balanced diet, human nutritional benets. National food-based dietary guidelines (FBDGs) in general do
not consider environmental sustainability in their recommendations41, however this is changing.
Although, most European FBDG recommendations advice to eat less red and processed meat and to
replace it with legumes, white meat, and sh42, still recommendations with regards to overall protein
intake levels are high. For example the Netherlands advices in its FBDG a protein intake of 98 g cap/day
(45 g ASP cap/day) and Sweden 85 g cap/day (56 g ASP cap/day)43. This clearly shows the potential for
improvement towards achieving the optimal ratios we present in this study. Therefore, we strongly
recommend further reducing the consumption of ASP and increasing the consumption of legumes to
redesign European FBDGs towards improving both human and planetary health.
Online methods
Circular food system model
This study is based on the Circular Food Systems model (CiFoS)28. CiFoS is a bio-physical data- driven
food system linear programming optimization model coded in GAMS44. The model was developed to
represent a circular food system with all its subsystems such as human nutrition, animal and plant-
production, capture and sheries, and waste streams.
Human nutrition

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In CiFoS, the daily recommended nutrient requirements advised by the European Food Safety Agency
(EFSA) for the EU28 are met to ensure a nutritious diet. The model covers 37 nutritional indicators
including macro and micronutrients, vitamins, amino acids, fatty acids and energy content. Vitamin D
and iodine recommendations were excluded as a nutritional requirement due to mandatory salt
fortication for iodine in the EU and implicit limitations in obtaining enough vitamin D from diets alone.
Nutritional content of the CiFoS products is based on the FoodData Central Data from USDA45. In
addition to nutrient requirements, food intake constraints per product and/or food family were included
based on the reference range of the EAT-Lancet dietary guidelines22. All scenarios apart from the
reference scenarios complied with the nutrient requirements and the EAT-Lancet diet22.
Land availability
The total area of agricultural land available in the EU28 is 172 mil ha.24 This land is divided in three
distinct land use types: arable land, marginal grassland, and rangelands. On arable land, temporary
grassland is a nested land use type that can be selected in crop rotations as any other crop. Land cover
maps for grassland were taken from the History Database of the Global Environment (HYDE)46 and
represent the year 2010, while the cropland was taken from IIASA-IFPRI47. Grassland was classied as
temporary when cropland and grassland land cover maps overlapped.
Plant production
CiFoS includes 43 food crops and 8 fodder crops including 3 different grass types. Production data of the
43 food crops are based on the Global Spatially-Disaggregated Crop Production Statistics Data for 2010
(Version 2.0) further referred to as SPAM48,49. Production data for the fodder crops were sourced from the
EARTHSTAT dataset “Harvested Area and Yield for 175 Crops”50. Yields and area data were spatially
extracted for climate-soil zones. These zones were created based on the intersection of the Global Agro-
ecological Zones51 and the IPCC default soil classes derived from the Harmonized World Soil Data
Base52. The Crop rotations were represented as fractions of areas based on the rotation break data53.
Fertilization is assumed to be balanced, meaning that we only fertilize as much as the nutrient uptake of
the plants plus the losses. The losses for nitrogen were calculated based on the IPCC54, while eld losses
for phosphorus were assumed to be 12.5% of application55.
Animal production
The animal system includes livestock (dairy, beef, pigs, broilers, layers) and farmed sh (Atlantic Salmon
and Nile Tilapia)56. The two farmed sh species function as proxies for salt and freshwater species. The
animal type determines the nutrient requirements and other characteristics such as the feed intake
capacity. Furthermore, the model includes the whole herd structure with parent stocks (e.g., sow in pig
system) and reproduction stocks (e.g., heifer in a dairy system) to account for the animal’s entire
lifecycle. The nal feed ration is a model outcome. To meet these requirements, the model can select
different feed ingredients ranging from co-products, food waste, grass resources, animal by-products, and
high quality biomass such as grains, which humans can also consume.

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Fisheries
The model further includes capture sheries as food and feed. Capture sheries provide sh for human
consumption and sh by-products which can be fed to animals. Landings of capture sheries are based
on a combined database of the RAM Legacy Stock Assessment57 and FAO marine capture data58.
Landings were assumed to be limited to the maximum sustainable yield (MSY) implemented in EU
legislation. This MSY represents the highest achievable landings without long-term negative impacts on
the population. A distinction was made between the edible yield fraction of all landed food-grade sh and
their non-edible by-products to account for feed-food competition.
Residual streams
The model represents different residual streams such as crop residues, by-products, food losses and
waste, manure, compost, and human excreta. Depending on the type and suitability, these streams can be
used as feed, fertilizer, or food. A more detailed description can be food in28 .
Greenhouse gas emissions
Greenhouse gas emissions arise from cropping and animal production systems and transportation. GHG
emissions from cropping systems are based on the direct and indirect emissions from N2O in relation to
soil and climate and fertilizer type59. For animal GHG emissions, we used the tier2 approach from the
IPCC methodology60. The precise way to calculate animal-based GHG emissions is described in 28. The
transportation of crops, animals and by-products is allowed between EU28 countries. These GHG
emissions are the result of transportation fossil fuel use. The emissions were calculated using the
distance between countries, the lorry size, and the emission factor per kilometre from evo-invent61.
Compost emissions were further accounted for by converting the N losses and the CH4 losses to CO2. All
emissions were converted to CO2 equivalents and summed to calculate the total amount of GHG
emission per food system.
Circular principles
Circularity was modelled following three major principles. First, animals can only be fed by low-cost
biomass that humans cannot or do not want to eat17. Farmed animals are then fed by all the supply
chain losses and co-products from food processing. Second, the edible ratio of animals is increased,
meaning that all edible parts of the farmed animals (i.e. offal) are consumed by humans. Third, nutrient
re-cycling is improved by preventing over-fertilization and fostering circular fertilization. Circular
fertilization makes use of leguminous crops in crop rotation, compost from organic waste streams and
crop residues to reduce articial fertilizer inputs.
Scenario description

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Reference scenario
The reference scenario xes the current agricultural land from FAOSTAT and minimizes the difference to
the FAO protein supply per food group8. Trade was only allowed between countries but not outside the
study boundaries. The reference is therefore a self-sucient production and consumption scenario for
the EU28 countries. The agricultural land is based on the MAPSPAM data48 and was scaled to the total
FAOSTAT areas per land use23,24. The current protein supply was derived from Food Balance Sheet (FBS)
element: “protein supply quantity (g/cap/day)”)8.
Protein intake scenarios
Two protein intake levels were dened to assess the effect of these levels on land use and GHG
emissions at a food system level. Current protein intake was calculated by subtracting consumption
losses from the protein food supply based on food groups (FAO-FBS element: “protein supply quantity
(g/cap/day)”)8,62. The current EU28 protein intake resulted in 82 g protein/cap/day. Recommended
protein intake was calculated by combining the EFSA average requirement (AR) of 0.66 g protein/kg body
weight with a 70 kg reference body weight9. This resulted in a recommended protein intake of 46 g
protein/cap/day, thus the difference between current and recommended protein intake is 36 g
protein/cap/day. The current ratio of around 60:40 between animal and plant sourced proteins was
calculated from the FBS8. To derive the amount of animal protein intake, current and recommended
protein intake were multiplied by 0.6 to result in an ASP intake of 49 and 28 g/cap/day, respectively
(Fig.4).
Protein transition scenarios
The protein transition from the current to a plant-based food system is modelled as a stepwise reduction
of ASP in the diet. The transition is modelled in four steps going from an ASP:PSP ratio of 60:40, 40:60,
20:80 to 00:100% (plant-based). For current total protein intake levels, an additional ASP:PSP ratio of
22:78 was added because the 20:80 ratio was nutrient inadequate (< 18 g ASP/cap/day), which led to
diculties in comparison with the other ratios.
Objective function and nal scenario denitions
We expanded the initial food systems model developed by 28 to quantify the effect of the protein
transition in EU28 on land use and GHG emissions. The adjusted model included a double optimization
option: rst the human nutrition gap was minimized, followed by minimizing either land use or GHG
emissions. In this manner, we ensured that model outcomes closely met the nutritional requirements for
macro and micronutrients (Fig.4). To model all the scenarios, we use four different objective functions
combined in three optimization scenario options (see ‘Objective function equations’ in Supplementary
information):

Page 14/22
1. Minimizing the positive and negative deviation to the FBS protein supply while xing the current total
agricultural land.
2. Minimizing the human nutrient gap + Minimizing the land use
3. Minimizing the human nutrient gap + Minimizing GHG emissions
By using one reference scenario, two different optimization approaches, with two protein intake scenario
levels and four protein transition step scenarios and the two ‘22:78’ scenarios, we generated a total of 19
scenarios. The basis of the scenarios is shown in Table3:
Table 3
Scenario parameters and associated assumptions for the modelling procedure.
Scenario Parameter Description/Assumption
All
protein
transition
scenarios
Use of Low-
cost
biomass
Low-cost biomass can be used as feed or fertilizer. Offal can be used as
food. All animal products have to be used either as food or as feed and
are not allowed as fertilizers. This is an important premise of a circular
food system17,27.
All Import,
Export No import or export from outside EU28. Trade between all countries is
allowed. Emissions through transport are considered.
All Animal
numbers Animal numbers are variable. Animals can have different intensity
levels, which is reected in their feed demand and related impact.
Reference Minimize
difference to
protein
supply
Minimizing the deviation to the protein supply by food group of the
FBS8.
Reference Fixing
agricultural
land
Fixing the current agricultural land to the baseline so it serves as a land
reference scenario per land type (arable land, grassland on arable land,
marginal grassland and rangeland) and crop group (e.g., cereals,
legumes, vegetables).
Protein
transition
(PT)
Meet human
nutrient
requirements
Human nutrition requirements have to be met as much as possible. We
included all macro (energy, fat, protein) and micro nutrients (minerals,
vitamins, fatty acids and amino acids).
Protein
transition
(PT)
Total protein
intake Total protein intake was either 82 (current) to 46 (recommended) g
protein/cap/day.
Protein
transition
(PT)
Animal
protein
intake
The current animal protein intake is derived by the ratio of 60:40
between animal and plant proteins (Table1).
Protein
transition
(PT)
Share of
animal
protein
intake
The ratio of ASP: PSP ranged between 60:40 to 0:100 for both protein
intake levels (Table1).


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Software and data analysis
All data transformation, analysis and visualization were performed using R (version 4.2.2)63. The
optimization modelling was performed using the General Algebraic Modeling System (GAMS)21.
Declarations
Data availability
The raw data have been deposited in a GIT repository and are available on request under a licence similar
to Creative Commons Attribution-Non Commercial-Share A like 4.0 International Public License.
Code availability
The model code has been deposited in a GIT repository and is available on request under a licence similar
to Creative Commons Attribution-Non Commercial-Share A like 4.0 International Public License.
Acknowledgements
This project received funding from the AVINA foundation (https://avinastiftung.ch/).
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Figures

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Figure 1
Step-wise reduction of animal source protein in different protein intake scenarios together with a total
representation of the nutrient gap for each protein transition step. (1) redesigning the food system under
circular principles at current ASP:PSP ratios. (2) Redesigning the food system based on the
recommended ASP:PSP ratio. (3) Redesigning a plant-based food system allowing for nutrient

Page 20/22
deciencies. Ref = Reference scenario, LU = Land use, GHG = Greenhouse gas emissions, cap = capita, ha
= hectare.
Figure 2
Relative crop shares of agricultural land per crop group, protein intake level and environmental impact
category. Min LU / Min GHG = Minimizing land use / greenhouse gas emissions. PI = Protein intake, Ref =
FAO Reference scenario.

Page 21/22
Figure 3
Selection of nutrients moving towards inadequacy per optimal scenarios. Nutrient units can be derived
from the facet labels in section (1). Abbreviations: B12 = Vitamin B12, EPA = eicosapentaenoic acid, DHA
= docosahexaenoic acid. 1A: Different fats, 1B: Macronutrients and Energy, 1C: Micronutrients, 1D:
Vitamins. Section (2) shows the nutrient inadequacy in % per inadequate nutrient and scenario (scenarios
with <18 gASP/cap/day).

Page 22/22
Figure 4
Modelling workow and main data source for dening current and recommended protein intake levels
(PIL). EFSA = European Food Safety Authority; FBS = Food Balance Sheet; PRI = Population reference
intake; BW = Body weight; LU = Land use; GHG = Greenhouse gas emissions.
Supplementary Files
This is a list of supplementary les associated with this preprint. Click to download.
SupplementaryInformationOptimalRatioNatureFood.docx
GraphicalAbstract.pdf