Association Between Nutritional Biomarkers and Low Muscle Mass, Obesity, and Low Muscle Mass with Obesity Across Physical Activity Levels Among U.S. Adults: Finding from the National Health and Nutrition Examination Survey 2015–2018

Background: Nutritional biomarkers are linked to body composition changes, but limited evidence has studied how nutritional biomarkers relate to low muscle mass, excess adiposity, and both coexisting conditions across different physical activity levels. This study aims to investigate associations between low muscle mass, obesity, and low muscle mass with obesity and nutritional biomarkers across physical activity levels among U.S. adults across physical activity levels. Methods: This cross-sectional study analyzed data from adults aged 20–59 years from the 2015–2018 cycles of the National Health and Nutrition Examination Survey (NHANES) 2015–2018. Low muscle mass was defined by low appendicular lean mass relative to body weight (LALM/W). Obesity was classified using body mass index (BMI1), waist circumference (WC2), and body fat percentage (FM%3), and low muscle mass with obesity was defined using three coexisting phenotypes (LALM/W-O1, LALM/W-O2, LALM/W-O3). Nutritional biomarkers included serum albumin, vitamin D, triglyceride, cholesterol, LDL cholesterol, iron, insulin resistance (HOMA IR), and high-sensitivity C-reactive protein (hs-CRP). Physical activity was categorized as inactive, insufficiently active, or sufficiently active based on MET minutes per week. Multivariable regression models accounted for the complex survey design and relevant covariates. Results: After adjustment, LALM/W was significantly associated with low serum albumin, low vitamin D, high triglyceride, high HOMA-IR, and high CRP. Obesity was significantly associated with low serum albumin, low vitamin D, high triglyceride, high LDL cholesterol, high HOMA-IR, and high CRP. LALM/W-O in all phenotypes were significantly associated with low serum albumin, low vitamin D, high triglyceride, high LDL cholesterol, high HOMA-IR, and high CRP. LALM/W-O phenotypes demonstrated the strongest associations, particularly with high HOMA-IR and hs-CRP. Although the associations varied by physical activity level, sufficiently active group was associated with lower odds of adverse nutritional biomarkers compared with insufficient activity. Conclusions: Nutritional biomarkers are associated with LALM/W and obesity. Sufficient physical activity was associated with fewer adverse outcomes. This suggests that adequate physical activity may be associated with better nutritional status and body composition.