Overfeeding polyunsaturated fat compared with saturated fat does not differentially influence lean tissue...

Fatty acids may influence lean tissue volume and skeletal muscle function. We previously reported in young lean participants that overfeeding PUFA compared with SFA induced greater lean tissue accumulation despite similar weight gain.

In a double-blind randomized controlled trial, we aimed to investigate if the differential effects of overfeeding SFA and PUFA on lean tissue accumulation could be replicated in individuals with overweight and identify potential determinants. Further, using substitution models, we investigated associations between SFA and PUFA concentrations with lean tissue volume in a large population-based sample (UK Biobank).

Sixty-one males and females with overweight [BMI (kg/m²): 27.3 (interquartile range (IQR), 25.4-29.3); age: 43 (IQR, 36-48)] were overfed SFA (palm oil) or n-6 (ω-6) PUFA (sunflower oil) for 8 wk. Lean tissue was assessed by MRI. We had access to n = 13,849 participants with data on diet, covariates, and MRI measurements of lean tissue, as well as 9119 participants with data on circulating fatty acids in the UK Biobank.

Body weight gain mean (SD) was similar in PUFA (2.01 ± 1.90 kg) and SFA (2.31 ± 1.38 kg) groups. Lean tissue increased to a similar extent [0.54 ± 0.93 L and 0.67 ± 1.21 L for PUFA and SFA groups, respectively, with a difference between groups of 0.07 (-0.21, 0.35)]. We observed no differential effects on circulating amino acids, myostatin, or IL-15 and no clear determinants of lean tissue accumulation. Similar nonsignificant results for SFA and PUFA were observed in UK Biobank, but circulating fatty acids demonstrated ambiguous and sex-dependent associations.

Overfeeding SFA or PUFA does not differentially affect lean tissue accumulation during 8 wk in individuals with overweight. A lack of dietary fat type-specific effects on lean tissue is supported by specified substitution models in a large population-based cohort consuming their habitual diet. This trial was registered at clinicaltrials.gov identifier as NCT02211612.