Article de Coline Capron (EnvIM 2020)


From the farm to the fork, food undergoes a lot of steps in the foodchain, contributing to greenhouse gas (GHG) emissions and climate change. As expressed by Garnett (2011), patterns of food consumption are responsible for about 15 to 28% of total GHG emissions in industrialised countries. The food system is also thought to be the primary global driver of the increase of obesity and malnutrition Payne et al (2016). An unbalanced lifestyle and food diet are indeed linked to the development of frequent chronical diseases encountered nowadays such as cancers, heart diseases, obesity (Inserm, 2018) etc.

Consumers’ diet evolution from a high to a low carbon footprint could be a mitigation lever to reduce GHG emissions in the food sector. New regulations promote access to low carbon meals in canteen and institutional catering1 (AEF info, 2021;Ministère de l’agriculture et de l’alimentation, 2019) and the French public health policy now includes environmental concerns to its nutritional recommandations2 (Inserm, 2020).

Moreover, French people do question themselves regarding the consequences of their consumption pattern. Indeed, in 2020, IFOP led a poll on a representative sample of 15 000 French people to evaluate the general trend of vegetarism and its variants (flexitarism and veganism mainly) in the country. 84% of people declared paying attention to the impact of food on their health and 62% affirmed they changed their consumption and lifestyle pattern because of climate change awareness (Ifop, 2021). Low-carbon diets have gained large visibility and their ideas reach other consumption patterns through meat reduction mainly.

But what makes a low carbon diet? What are its impacts on health? This blog article will try to show the origin of carbon emissions in the food system and food diets as well as enlighten on low carbon diets implication on health.

The French food system footprint represents nearly one quarter of total household emissions and is largely represented by agriculture production. The total footprint derived from the main stages of the food system (agricultural production, processing, freight transport, distribution, out-of-home eating, travel for household food purchases and food preparation in the home) is estimated at 163 MtCO2eq, i.e 24% of the household carbon footprint in France, in relation to the total carbon footprint estimated by the Service de l’Observation et des Statistiques of 671 MtCO2eq for 2012. This amount is likely to be underestimated as deforestation associated to land use is not included in the calculations3 (Barbier et al., 2019).


Carbon balance by sector for households’ food consumption (Barbier et al., 2019) OHE : out of home eating ; includes emissions of imported food products ; excludes emissions of exported food products
Carbon balance by sector for households’ food consumption (Barbier et al., 2019) OHE : out of home eating ; includes emissions of imported food products ; excludes emissions of exported food products


As observed on the graph above, the largest GHG emitter in the food system (two-thirds of the total carbon footprint) is agricultural production (about 109 MtCO2eq).

Animal production along with the agricultural practices used are crucial components of the total household carbon footprint. Methane and nitrous oxide are GHGs characteristic of this sector, accounting for 29% and 23% of the total household carbon footprint.

  • Methane CH4 is mainly derived from enteric fermentation by ruminants and livestock effluents management
  • Nitrous oxide N2O is related to the nitrogen cycle in the agrosystem : nitrogen leaching, volatilization and deposition from livestock effluents management, storage and manure spreading conditions, as well as synthetical fertilizers use

CO2 is emitted for the rest of the share, due to the use of urea as a synthetical fertilizer, liming (for soil acidity management) and energy consumption on the farm.

Food derived from animal production has a bigger impact on GHG emissions compared to other types of foods. Animal production for food consumption encompasses meat, fish, milk and egg production, from a various selection of species. In their study, J. Poore and T. Nemecek (2018), consolidated life cycle assessment data for 40 products, representing 90% of global protein and calorie consumption. They based their work on 570 studies, gathering data from 38,700 farms in 119 countries, processors, packaging types and retailers. On the graph below, you can see the represented GHG emissions of the 40 products, grouped by their primary dietary role.


Estimated global variation in GHG emissions within and between 40 major foods, (A) Protein-rich products, (B) Milks, (C) Starch-rich products, (D) Oils, (E) Vegetables, (F) Fruits, (G) Sugars, (H) Alcoholic beverages (1 unit = 10mL of alcohol), ABV : Alcohol by volume), (I) Stimulants n=number of farm or regional inventories – pc and pctl = percentile (Poore & Nemecek, 2018)
Estimated global variation in GHG emissions within and between 40 major foods, (A) Protein-rich products, (B) Milks, (C) Starch-rich products, (D) Oils, (E) Vegetables, (F) Fruits, (G) Sugars, (H) Alcoholic beverages (1 unit = 10mL of alcohol), ABV : Alcohol by volume), (I) Stimulants n=number of farm or regional inventories – pc and pctl = percentile (Poore & Nemecek, 2018)


As an example, for the same primary nutritional benefit of providing 100g of proteins, beef is the most emitting food, with a mean of 50 kgCO2eq, when grains or peas emit an average of 2.7 and 0.4 kgCO2eq respectively. J. Poore and T. Nemecek showed that the impacts of the animal product with the lowest emission rate outweighs the average impacts of substitute vegetable proteins across GHG emissions (as well as for the other studied impacts such as eutrophication, acidification and frequently, land use) providing evidence for the importance of dietary changes.

The importance of GHG emissions for animal production can mainly be explained as deforestation for agriculture is dominated (67%) by animal feed (soy, maize, and pasture), resulting in losses of carbon sinks, (and biodiversity!). Also, animal feed to edible protein conversion ratios are greater than two for most animals. Indeed by-products used as animal feed have low digestibility and additional transport is often required to route feed to livestock. And as mentioned above, animals create additional emissions from enteric fermentation and manure (CH4, N2O) (Poore & Nemecek, 2018).

Beyond the important variations in GHG emissions between products, the authors also assessed high variations in impact among producers. Indeed, for beef, the 10th percentile is of 20 kgCO2eq which means that 10% of the 724 studied farms had their beef’s GHG emissions equal or below this value, where the 90th percentile is of 105 kgCO2eq. This implies substantial potential to reduce environmental impact at the production level.

Replacing only beef or all the meat (beef, pork, poultry) in consumers’ diet can reduce the GHG emissions associated with diets by an average of 9% up to 50% depending on the type and degree of substitution (Willits-Smith et al., 2020). As observed on the previous graph, GHG emissions between animal species are not equal : beef, which is a ruminant species, emits methane through eructation during the enteric fermentation, responsible for larger contributions than pork or chicken. A cow milk based product like cheese, also emits more GHG than plant-based proteins as its raw material comes from emitting animal species.

Thanks to targeted simple substitutions, shifts towards less impactant food diets on the environment could be progressively eased, as represented on the graph below. In this study led by Willits-Smith et al., (2020), 1026 Americans were identified as potential changers of their diet. The impact of their food diets was assessed against GHG emissions before and after the implementation of substitutions. Replacements were made in equal calorie amount. The alternative diets presented implied food substitution within the same product category (other animal products) or between product categories (meat for plant products).


GHG emissions (kgCO2eq/day) from protein foods in potential changers before and after hypothetical changes in food diets of american participants (Willits-Smith et al., 2020) All replacements were made in equal calorie amount  
GHG emissions (kgCO2eq/day) from protein foods in potential changers before and after hypothetical changes in food diets of american participants (Willits-Smith et al., 2020) All replacements were made in equal calorie amount


As we expected, the greatest reductions come from substituting plant-proteins4 food for all beef, pork and poultry intake (49,6% reduction). However, replacing just the beef intake would account for more than 80% of this reduction (Willits-Smith et al., 2020). To be noted that substitutions should be recontextualized in their cultural environment where countries, regions have their own cultural pattern of consumption and “starting point” in terms of food diet. Moreover, substitution promotion for locally produced food might be of interest if advantageous in terms of GHG emissions.

On the overall picture of an individual assessment of GHG emissions, Carbon 4, a consulting company specialized in energy transition and adaptation to climate change, estimated that the individual action of converting from a carnivorous to a low carbon diet such as a vegetarian diet could reduce the individual total GHG emissions (comprising food consumption, mobility, the use of goods and services and housing) by 10%, representing the biggest impact of the dozen actions that fall within the « everyday gestures » to reduce individual carbon footprint (Dugast & Soyeux, 2019).

However, a low carbon diet isn’t necessarily a healthier diet. In their work, Payne et al. (2016) reviewed the results of 16 published studies that link GHG emissions of 100 dietary patterns to nutritional content (nutrients to limit, micronutrient content) or associated consequences for health (cardio-vascular diseases, cancer, mortality). Overall, 346 cases of effects of diets with reduced GHG emissions on nutritional quality or health outcomes were yielded. Results of the study showed highly heterogenous outcomes, but general trends were highlighted. For diets low in animal products (and reduced in GHG emissions), saturated fat and salt were reduced in 57 cases out of 84. However diets with reduced GHG emissions were often high in sugar (38 cases out of 55) and low in essential micronutrients (129 cases out of 158). For micronutrients, there was a decrease in calcium, and in vitamin B12, likely to be due to the decrease in consumption of animal food, especially dairy products. To the contrary, higher Fe intake was slightly associated with lower GHG emission diets (the reason is unclear). Overall, 64% (n = 214) of dietary links showed that reduced GHG emissions from diets were associated with worse health indicators. One of the main limits identified in Payne et al., (2016) review was that the majority of the studies modeled diets based on their perceived ‘healthiness’ according to nutritional criteria, and the current knowledge in the field. Payne et al., (2016) results were confirmed by Doro & Réquillart (2020) who showed that “diets with a lower impact on climate might also be healthier, but this is not systematic » also, « healthier diets might be accompanied by a reduction in GHG emissions, but this is not systematic ».

When looking at food diets impact on health, the way food is produced and processed also becomes an interesting topic. Indeed, the BioNutriNet program that investigates the impact of food on health and the environment showed that regular organic food consumers compared to non organic food eaters were healthier. They presented a reduced risk of obesity of 31%, a reduced risk of declaring a metabolic syndrome of 31% (diabete or heart disease) and cancer of 25% (all things equal otherwise) (Pointereau, 2019). The explanation was a lower exposure to ingested pesticides and contaminants thanks to the organic farming way of production. And what about GHG emissions ? Food diet carbon footprint of regular organic consumers showed a reduction by 37% in GHG emissions compared to conventional consumer’s food diet. This difference was mainly due to their largely plant-based diet (+21% of plant proteins) compared to conventional eaters’ (Pointereau, 2019).

Ultra-processed food, commonly used by plant-based diet eaters is subject of research for health issues. Vegetarian ultra-processed food nowadays flourish in the dietetic section of supermarkets. Gehring et al. (2021) studied the consumption of ultra-processed foods (UPFs) by plant-based diet eaters. They showed that a “higher avoidance of animal-based foods was associated with a higher consumption of UPFs », with a reduced benefit on health because of potential adverse effects on nutritional quality. Additives, which appear in ultra-processed food are suspected of negative impacts on health (higher cancer risk, with suspicion of cardio-vascular disease and death impacts) and their cumulative effects are not yet known (Inserm, 2018).

As shown in this article, not all low carbon diets are healthy. Because of the complex complementarities between food products, it is not guaranteed that substitutions of food with the objective of reducing diet’s impact on GHG emissions will lead to better health. The French public policy for nutrition and health of 2017 shows promising results in combining these two objectives, as 50% of GHG emissions and 35 000 premature deaths (of cardiovascular disease) were estimated to be avoided following its recommendations. However, it implied a higher cost of about 1€/day/person (Inserm, 2020) compared to the previous recommendations. Understanding the underlying socio-economic factors influencing food consumption behaviors, will be key to design policies promoting sustainable changes in diets. Straightforward information to consumers could also facilitate this transition process. On July the 20th of 2021, the French “Climate and resilience” law adopted the implementation of an environmental display for food products by 2022-2023, largely inspired with the Nutriscore label for nutritional display. Then, French people should be better informed to take motivated dietary decisions for climate.





1 On the 20th of July 2021, the French law project called “Climat et resilience” was adopted by the Parliament. It obligates all schools to propose at least one vegetarian meal a week. This decision follows the two years experiment that had been launched through the Egalim law in 2019. Moreover, a vegetarian option must be proposed daily in all of the school restaurants managed by the state from January 2023.

2The « Programme national nutrition santé » of 2017.

3 Also called LULUCF : Land Use, Land-Use Change and Forestry.  

4Plant proteins : legumes, nuts and seeds (Willits-Smith et al., 2020)



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