Plant and animal protein intakes are differentially associated with diet quality and obesity: findings from the Australian National Nutrition and Physical Activity Survey of Australian Adults

Dietary guidelines often combine plant and animal protein intake recommendations, yet evidence suggests they may have distinct associations with health. This study aimed to examine relationships between animal and plant protein intake, using different classification approaches, and diet quality and obesity. Plant and animal protein contents of foods reported by 7637 participants (≥ 19 years) during the 2011-2012 National Nutrition and Physical Activity Survey were estimated using Australian food composition databases. Usual animal, plant and total protein intakes were estimated using Multiple Source Methods. Diet quality was assessed using the 2013-Dietary Guidelines Index (DGI), and obesity measures included BMI and waist circumference (WC). Multiple linear and logistic regressions were performed and adjusted for potential confounders. Plant and animal protein intakes were positively associated with DGI scores (plant protein: men, <i>β</i> = 0·74 (95 % CI: 0·64, 0·85); women, <i>β</i> = 0·78 (0·67, 0·89); animal protein: men, <i>β</i> = 0·15 (0·12, 0·18); women, <i>β</i> = 0·26 (0·22, 0·29)). These associations were consistent when examining high-quality plant protein (high-protein-containing plant-based foods with comparable nutritional values to animal proteins) and non-dairy animal protein intakes. Plant protein intake was inversely associated with BMI and WC in men but not women. Animal protein intake was positively associated with BMI in both sexes and WC in men only. Men's plant protein intake was inversely associated with obesity (OR = 0·97 (0·96, 0·99)) and central obesity (OR = 0·97 (0·95, 0·98)). Further studies are needed to examine the influence of different animal protein sources by accounting for energy intake and sex-specific associations.