Effect of Three Different Daily Protein Intakes in a Two-Meal Eating Pattern on Protein Turnover in Middle Age and Older Adults: A Randomized Controlled Trial

Background: Reduced meal frequency patterns have become popular for weight loss, maintenance, and improving cardiometabolic health. The extended fasting windows with these dietary patterns could lead to greater protein breakdown, which is a concern for middle-age and older adults who may need higher protein intakes to maintain or increase net protein balance.

Objective: The purpose of this study was to quantify muscle and whole-body protein kinetic responses to three different daily protein intakes within a two-meal eating pattern.

Methods: Thirty participants (age: 61 ± 6 years, body mass index: 26.5 ± 4.8 kg/m²) participated in this 24-hour metabolic study using oral stable isotope tracer techniques and were randomized to one of three protein intakes: 1) recommended dietary allowance (RDA): 0.8 g/kg/day; 2) habitual US intake: 1.1g/kg/day; or 3) ≈2RDA: 1.5g/kg/day distributed across two meals, consumed within a 9-hour window.

Results: Whole-body net protein balance was significantly higher for 1.5g/kg/day compared with 0.8 g/kg/day (mean difference: 0.55 g/kg LBM/d; 95%CI: 0.17 to 0.93 g/kg LBM/d; p=0.004) and 1.1g/kg/day (mean difference: 0.6 g/kg LBM/d; 95%CI: 0.23 to 0.97 g/kg LBM/d; p=0.001), with no difference between 0.8 and 1.1g/kg/day (mean difference: 0.05 g/kg LBM/d; 95%CI: -0.31 to 0.40 g/kg LBM/d; p = 0.936). Muscle protein synthesis was not significantly different between any groups (p = 0.388).

Conclusions: Within a two-meal eating pattern, a protein intake of 1.5 g/kg/day led to more positive whole-body net protein balance than intakes of 0.8 and 1.1 g/kg/day in middle age and older adults.

Trial registration: ClinicalTrials.gov identifier: NCT04830514.