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 defined 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 deficiencies. 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).
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 findings. 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 (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 first 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 artificial 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
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).
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 profile (especially for soybeans), and the ability of legume crops to fix atmospheric nitrogen, thereby reducing the amount of artificial 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.
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: first, fatty fish 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, fish have an efficient protein conversion ratio; compared to other animal production systems, they need less nutrients to produce proteins for human consumption25. Last, fish production - especially offshore salmon – does not require agricultural land as long as no additional feed has to be grown, making it the most land efficient animal type when minimizing land use. In addition to an increase in fish in paradigm 1, broiler meat also increased (current protein intake) while land use was reduced. Similar to fish, broilers have an efficient 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-specific 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).