Effect of increasing plant protein intake on protein quality and nutrient intake of US adults

Three cycles of NHANES (2013-2018) were used to assess protein intake, protein quality (protein digestibility-corrected amino acid score; PDCAAS), protein cost, and nutrient intakes across quartiles of plant protein intake (Q1: <28.2%; Q2: 28.2% to <32.1%; Q3: 32.1 to <36.2%; Q4: ≥36.2%) over a 24 h period (≥19 years, n = 14 888). Grains represented the primary source of plant protein across quartiles and increased from 5.01% (Q1) to 13.5% (Q4). Across all the USDA's Food and Nutrient Database for Dietary Studies (FNDDS) food groups, grains were the most economical source of protein (24.3-26 g protein/$1). Legumes were the most economical plant-based protein (28-37.7 g protein/$1) within the "Protein Foods" FNDDS group. Absolute protein intake (96.6 g/day) and PDCAAS (0.91) of diets were progressively lower from Q1 to 72.0 g/day and 0.8 in Q4, respectively. Modelling the replacement of 50% of amino acids from grains in the diet with amino acids from legumes increased the PDCAAS by 10% in Q4. Intake levels of fibre, folate, iron, and zinc, were higher in Q2-Q4 compared to Q1 but had lower intakes of vitamins B12 and D. Amino acid complementation is required to effectively integrate higher levels plant protein into US diets.