Shifting towards a more plant-based diet, as promoted in Western countries, will reduce the animal protein contribution to total proteins. Such a reduction may not only impair protein adequacy, but also the adequacy in other nutrients. Using dietary data from a French, cross-sectional, representative survey, we determined for five French subpopulations (namely 1) women < 50 y; 2) women 50–64 y; 3) women ≥ 65 y; 4) men < 65 y; and 5) men ≥ 65 y), the minimum total protein level and the minimum animal protein contribution to total proteins that are compatible with the fulfilment of all nonprotein nutrient-based recommendations. For each subpopulation, linear programming optimization was used to assess the minimum protein level (model set #1) and the minimum animal protein contribution to total proteins (model set #2) compatible with the fulfilment of all nutrient-based recommendations (except proteins, for which levels were analysed as outputs). Total diet costs were not allowed to increase. Eating habits were considered in model set #2 only. The minimum amount of protein that was theoretically compatible with the fulfilment of nutrient-based recommendations (model set #1) was below the minimum recommended protein intake for all subpopulations except women < 50 y. In model set #2, for women and men ≥ 65 y, decreasing animal protein contributions to total proteins below 55% and 60%, respectively, led to protein levels below recommended levels. For the other subpopulations (women < 50 y, women 50–64 y, and men < 65 y), the lowest animal protein contributions to total proteins compatible with a nutritionally adequate diet (including protein adequacy) were 55%, 50%, and 45%, respectively.
