Plant to animal protein ratio in the diet of the elderly: potential for increase and impacts on nutrient adequacy and long-term health-a diet optimization study.

Background: The percentage of plant protein in the diet (%PP) is increasing in high-income countries, but concerns exist regarding the elderly, who may require more protein and indispensable amino acids (IAA) than younger adults, although this remains debated.

Objectives: We aimed to assess how much %PP can be safely increased in older adults depending on estimated protein requirement, and identify nutritional issues and dietary levers as %PP increases.

Methods: Observed diets were extracted from dietary intakes of ≥65 y French adults (INCA3, n = 433). Using diet optimization, we modeled diets with graded %PP values ensuring full nutrient adequacy-applying constraints on energy and 34 nutrient intakes (accounting for bioavailability) and considering standard or higher protein requirements (reference intakes of 0.83 or 1 g/kg/d, respectively)-while minimizing chronic disease risk from specific food group over- or underconsumption (based on Global Burden of Disease data), with only as much departure from dietary habits as necessary.

Results: All modeled diets differed markedly from the current unhealthy diet. Whatever the protein requirement considered, the same ∼25%-70% %PP range was compatible with minimal chronic disease risk and full nutrient adequacy. As %PP increased, iodine, calcium, eicosapentaenoic acid+docosahexaenoic acid, bioavailable iron, vitamins A, B12, and riboflavin became critical; protein was only a concern at high requirement; IAA were never problematic under protein adequacy. Sensitivity analysis revealed that raising consumption limits for legumes, nuts, vegetables, and fruit could broaden the adequate %PP range by supplying more limiting nutrients.

Conclusions: Diets must be sufficiently rich in protein to ensure protein adequacy at higher requirements, with no risk of IAA inadequacy when protein intake is sufficient. For sustainability, %PP can potentially increase from the current ∼1/3 to ∼2/3 in an aging population while improving health and nutrient adequacy, provided sufficient seafood and dairy products remain. Further increases would require nutrient fortification/supplementation and/or new foods.