Modeled gradual changes in protein intake to increase nutrient adequacy lead to greater sustainability when systematically targeting an increase in the share of plant protein.

In line with sustainability issues, we are currently seeing a transition towards a lower consumption of animal protein. How ongoing gradual rearrangements in protein patterns impact sustainability and climatic change remains unknown. We used data from a French representative survey and selected for each individual the dual substitution of a serving of a protein food that most improved nutritional adequacy (using the probabilistic PANDiet score), with an increase in the percentage of plant protein required (SP) or not (SN). This was iterated 20 times incrementally, and we monitored the evolution of sustainability endpoints, including greenhouse gas emissions (GHGE) and predicted premature deaths avoided. After 20 iterations, the plant protein intake (31.1% total protein) decreased under SN (30.0%) and increased under SP (37.7%). The food groups whose contribution to protein intake increased the most were legumes (+ 225%), fatty fish (+ 151%), and lean chicken (+ 82%) under SN and legumes (+ 502%), pizzas and quiches (+ 190%), and fatty fish (+ 102%) under SP. The PANDiet score rose slightly more under SN (+ 7.5 ± 0.1) than SP (+ 6.2 ± 0.1). GHGE levels increased from 5.4 ± 0.05 to 5.7 ± 0.04 kg eq.CO2/day under SN and decreased to 5.1 ± 0.04 under SP. Diet costs increased from 7.4 ± 0.06 to 8.2 ± 0.05 €/day under SN and 7.6 ± 0.05 under SP. Predicted avoided premature deaths annually in France were 2200 (1700; 2700) under SP and 1700 (1400; 2000) under SN. In those series of small realistic changes in the individual diets, systematically increasing the plant share slightly limits the gain in nutritional adequacy but result in diets that are far more sustainable. [ABSTRACT FROM AUTHOR]