Plant to animal protein ratio in the diet: nutrient adequacy, long-term health and environmental pressure

Background Animal and plant protein sources have contrasting relationships with nutrient adequacy and long-term health, and their adequate ratio is highly debated. Objective We aimed to explore how the percentage of plant protein in the diet (%PP) relates to nutrient adequacy and long-term health but also to environmental pressures, to determine the adequate and potentially optimal %PP values. Methods Observed diets were extracted from the dietary intakes of French adults (INCA3, n=1 125). Using reference values for nutrients and disease burden risks for foods, we modeled diets with graded %PP values that simultaneously ensure nutrient adequacy, minimize long-term health risks and preserve at best dietary habits. This multi-criteria diet optimization was conducted in a hierarchical manner, giving priority to long-term health over diet proximity, under the constraints of ensuring nutrient adequacy and food cultural acceptability. We explored the tensions between objectives and identified the most critical nutrients and influential constraints by sensitivity analysis. Finally, environmental pressures related to the modeled diets were estimated using the AGRIBALYSE database. Results We find that nutrient-adequate diets must fall within the ∼15%-80% %PP range, a slightly wider range being nevertheless identifiable by waiving the food acceptability constraints. Fully healthy diets, also achieving the minimum-risk exposure levels for both unhealthy and healthy foods, must fall within the 25%-70% %PP range. All of these healthy diets were very distant from current typical diet. Those with higher %PP had lower environmental impacts, notably on climate change and land use, while being as far from current diet. Conclusions There is no single optimal %PP value when considering only nutrition and health, but high %PP diets are more sustainable. For %PP>80%, nutrient fortification/supplementation and/or new foods are required. ### Competing Interest Statement HF has received a research grant by INRAE from Roquette. FM has received research grants as PhD fellowships under his direction by AgroParisTech and INRAE from Terres Univia and Ecotone foundation, under the aegis of Fondation de France. ### Funding Statement This study did not receive any funding. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Source data for human data (dietary survey and related files) were openly available before the initiation of the study. They are located at . I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Data described in the manuscript will be made available upon request pending application and approval. * ANSES : French Agency for Food, Environmental and Occupational Health and Safety CIQUAL : French Information Centre on Food Quality DALYs : Disability-adjusted life-years DD : Diet departure criterion GBD : Global Burden of Diseases GHGe : greenhouse gas emissions HR : Health risk criterion INCA3 : Third Individual and National Study on Food Consumption French Survey %PP : Percentage of plant protein in the diet TMREL : Theoretical minimum risk exposure level