Protein valuation in food choice is positively associated with lean mass in older adults: Protein valuation and fat-free mass index

Background: Calorie-for-calorie, protein is more satiating than carbohydrate or fat. However, it remains unclear whether humans perceive calories derived from these macronutrients equally and whether lean mass is associated with a tendency to ‘value’ protein when dietary decisions are made. 
Objective: This study aimed to determine the test-retest reliability of a novel method for quantifying macronutrient valuations in human volunteers and to determine whether ‘protein valuation’ is associated with a higher fat-free-mass index in older adults.  
Design:A two-alternative, forced-choice task in which 25 foods were compared in 300 trials was undertaken in two studies. In study 1, participants (age range 19-71 years, n= 92) attended two test sessions, spaced one week apart. In study 2, older adults (age range 40-85 years; n= 91) completed the food-choice task and assessed the test foods for liking, expected satiety, and perceived healthiness. Body composition and habitual protein intake were assessed in both studies. Data was analyzed using individual binomial logistic regressions and multi-level binomial logistic regressions.
Results:In study 1, measures of macronutrient valuation showed excellent test-retest reliability; responses in the forced choice task were highly correlated (week 1 vs week 2; protein r= 0.83, P< 0.001; carbohydrate, r= 0.90, P<0.001; fat r= 0.90, P< 0.001). Calorie-for-calorie, protein and carbohydrate were stronger predictors of choice than fat (P<0.001). In study 2, protein was a stronger predictor than both carbohydrate (P=0.039) and fat (P=0.003), and a positive interaction was observed between protein valuation and fat-free mass index (OR=1.64; 95% CI: 1.38, 1.95; P<0.001). This was the case after controlling for age, gender, liking for foods, and habitual protein consumption. 
Conclusions: Together, these findings demonstrate that adult humans value calories derived from protein, carbohydrate, and fat differently, and that the tendency to value protein is associated with greater lean mass in older adults.