Combined Increases in Muscle-Strengthening Activity Frequency and Protein Intake Reveal Graded Relationship with Fat-Free Mass Percentage in U.S. Adults, NHANES (1999-2004).
Level 4 - case-series / case-control
Cross-sectional observational analysis of survey data (NHANES)
PubMed 27031912 · doi:10.14283/jfa.2015.37
What was done
Investigators analyzed cross-sectional data from non-institutionalized US adults aged 20–49 years across three cycles of the National Health and Nutrition Examination Survey (NHANES 1999–2004; 2,499 males, 2,373 females; total n=4,872). They examined independent and combined associations of muscle-strengthening frequency (MSF, self-reported times per week) and dietary protein intake (g/kg/day from a 24-hour recall) with fat-free mass percentage (FFM%) measured via bioelectrical impedance analysis. Multiple linear regression models controlled for education, race-ethnicity, standing height, and total caloric intake.
What was found
Each one-unit increase in MSF was associated with higher FFM% in males (β = 0.6 ± 0.1%) and females (β = 0.4 ± 0.1%). Each 1 g/kg/day increase in protein intake was associated with higher FFM% in males (β = 3.5 ± 0.4%) and females (β = 5.9 ± 0.4%). Independent of protein intake, participants meeting recommendations (MSF ≥ 2 times/week) versus non-exercisers (MSF = 0) had higher mean ± SE FFM% (males: 77.9 ± 0.5% vs. 74.4 ± 0.4%; females: 63.0 ± 0.4% vs. 60.7 ± 0.3%). Independent of MSF, individuals consuming above the Recommended Dietary Allowance (>0.8 g/kg/day) versus below had higher mean ± SE FFM% (males: 75.6 ± 0.4% vs. 74.0 ± 0.6%; females: 62.0 ± 0.4% vs. 58.2 ± 0.6%). The subgroup with the highest FFM% comprised males with MSF ≥ 2 times/week and protein intake > 1.4 g/kg/day (mean ± SE: 80.9 ± 0.73%).
Why it matters
This study shows a graded, additive association between muscle-strengthening exercise frequency, protein consumption, and relative lean mass in non-elderly adults, highlighting modifiable lifestyle targets to maintain muscle mass prior to older age.
Limits
The cross-sectional design precludes establishing causality or temporal order. Muscle-strengthening activity was self-reported without measures of exercise load or duration, and dietary intake relied on a single 24-hour recall subject to recall bias. FFM% was estimated using bioelectrical impedance rather than dual-energy X-ray absorptiometry or magnetic resonance imaging.
Cited by
- contradicts Analysis of the NHANES database revealed no correlation between muscle mass and strength training history, indicating that higher muscle mass in that survey population was driven by higher total body mass.