(LB02-09-25) Intakes of Protein, Essential Amino Acid, and Leucine Predict Body Mass Index (BMI) and Body Composition Among Individuals With History of Attempted Weight Loss

Objectives: Higher protein diets are associated with greater weight loss and may help preserve skeletal muscle during weight loss by stimulating muscle protein synthesis. Essential amino acids (EAA), in particular leucine, strongly stimulate muscle protein synthesis. This secondary analysis examined associations of protein, EAA, and leucine intakes with BMI and body composition among individuals with a history of attempted weight loss with varying degrees of success.

Methods: This study included participants (n=196) enrolled in an ancillary study of the International Weight Control Registry between Aug 2022 and Jan 2023. Data collection was conducted remotely over 3 weeks. Intakes of protein, EAA, and leucine were estimated by means of three 24-hr dietary recalls. Body weight and composition were measured daily using Garmin Index S2 scale. To calculate BMI, height was manually entered by participants into Garmin Connect app. Regression analysis adjusted for age was used to evaluate whether intakes of protein (g/kg body weight/d), EAA (mg/kg/d), and leucine (mg/kg/d) predicted BMI, % body fat, and % muscle mass.

Results: Participant characteristics were mean (SD) age 53.7±13.5 years, 84% females, 76% non-Hispanic White, and BMI 31.6±8.0 kg/m². Protein intake negatively predicted BMI (β [95% CI]=-4.46 [-5.39, -3.52], p< 0.001) and % body fat (β [95% CI]=-2.65 [-3.37, -1.94], p< 0.001), and positively predicted % muscle mass (β [95% CI]= 0.81 [0.37, 1.25], p=0.0003). Similar associations were observed for intakes of EAA and leucine. EAA intake negatively predicted BMI (β [95% CI]=-4.16 [-5.11, -3.20], p< 0.001) and % body fat (β [95% CI]=-2.41 [-3.14, -1.68], p< 0.001), and positively predicted % muscle mass (β [95% CI]= 0.73 [0.29, 1.17], p=0.001). Leucine intake negatively predicted BMI (β [95% CI]=-4.19 [-5.14, -3.23], p< 0.001) and % body fat (β [95% CI]=-2.43 [-3.16, -1.71], p< 0.001), and positively predicted % muscle mass (β [95% CI]= 0.73 [0.29, 1.17], p=0.001).

Conclusions: Among adults who have attempted weight loss, higher intakes of protein, EAA, and leucine were associated with lower BMI and % body fat, and higher muscle mass. Additional research, particularly randomized trials, are warranted to examine the effects of EAA and specific amino acids on body weight and composition.

Funding Sources: Medifast, Inc., NIH (T32DK062710, 3P30DK056336-19S1, P30DK048520-26)