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In a surprising turn from previous findings, a recent study published in the American Journal of Clinical Nutrition suggests that dietary n-6 polyunsaturated fatty acids (PUFA) might not have the touted benefits of promoting greater lean tissue accumulation compared to saturated fatty acids (SFA) in middle-aged individuals grappling with overweight or obesity.
Led by Fredrik Rosqvist from the Department of Public Health and Caring Sciences, Clinical Nutrition and Metabolism at Uppsala University, Sweden, the study delved into the effects of overfeeding on lean tissue mass in 61 participants with an average age of 42 years and a mean body mass index of 28.
Contrary to prior assumptions, the results from this double-blind randomized controlled trial (RCT) unveiled that overfeeding with either PUFA or SFA over an 8-week period did not result in differential impacts on lean tissue accumulation. Participants were randomly assigned to consume muffins enriched with either sunflower oil (rich in PUFA) or palm oil (rich in SFA) in addition to their regular diet.
Throughout the study, both groups exhibited a similar increase in body weight and lean tissue mass. Notably, the extent of lean tissue accumulation varied significantly among individuals within both the PUFA and SFA groups, emphasizing the complex interplay of factors influencing body composition.
Moreover, the study explored potential metabolic markers associated with lean tissue accumulation, such as circulating amino acids, myostatin, and interleukin-15 levels, finding no discernible differences between the two dietary groups. These findings cast doubt on the previously assumed benefits of PUFA over SFA in promoting lean tissue growth.
The study’s conclusions were reinforced by analysis from the UK Biobank cohort, although the associations between circulating fatty acids and lean tissue accumulation appeared to be ambiguous and sex-dependent.
However, several limitations temper the generalizability of these findings. The hypercaloric conditions of the RCT and the absence of resistance exercise in the study protocol raise questions about real-world applicability. Additionally, measurements of metabolite levels were confined to circulation rather than direct assessment in skeletal muscles.
Despite these limitations, the study sheds new light on the intricate relationship between dietary fat composition and lean tissue accumulation, particularly in the context of overweight and obesity in middle-aged individuals.
Commenting on the implications of their research, the authors noted that the observed phenomenon of greater lean tissue accumulation associated with PUFA in young lean individuals could not be replicated in this population subset.
The study received funding from various sources, including the Swedish Research Council and the Swedish Diabetes Foundation. Disclosure statements revealed financial support and potential conflicts of interest related to one of the authors’ affiliations with Antaros Medical.
In essence, while the study challenges prevailing beliefs regarding the differential effects of PUFA and SFA on lean tissue accumulation, further research is warranted to elucidate the complex interplay of dietary factors, metabolism, and body composition in diverse populations.
Source: Rosqvist, F. et al. “Differential effects of overfeeding of saturated or polyunsaturated fat in older compared with younger adult men.” American Journal of Clinical Nutrition (Year Published).
