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2 weeks ago
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TOPLINE:
In contrast to earlier findings in young lean individuals, dietary n-6 polyunsaturated fat acid (PUFA) doesn't promote greater lean tissue accumulation than saturated fat acid (SFA) in middle-aged individuals with overweight or obesity.
METHODOLOGY:
- A previous study showed that dietary n-6 PUFA led to greater lean tissue accumulation during weight gain than SFA in young lean individuals, but the effect of PUFA needs to be elucidated in middle-aged individuals with overweight and obesity.
- In this double-blind randomized controlled trial (RCT), researchers investigated the differential effects of overfeeding SFA or PUFA on lean tissue accumulation in 61 participants (mean age, 42 years) with overweight (mean body mass index, 28).
- Participants were randomly assigned to eat muffins containing either sunflower oil (high in PUFA) or palm oil (high in SFA), in addition to their usual diet for an 8-week overfeeding period, followed by a low-calorie diet for 4 weeks.
- The primary outcome was a change in lean tissue mass during the 8-week overfeeding period, assessed using MRI.
- Substitution models were used to validate the results of this RCT in a subsample of 13,849 participants (with data for diet, covariates, and MRI measurements of lean tissue) and 9119 participants (with data on circulating fatty acids) from the UK Biobank cohort.
TAKEAWAY:
- In the RTC, overfeeding either PUFA or SFA led to a similar increase in body weight and lean tissue in both groups.
- Between individuals in both groups, however, the lean tissue accumulation varied greatly in both the PUFA and SFA groups, with values ranging from −3.14 kg to +4.14 kg.
- Neither PUFA nor SFA showed any differential impact on the circulating amino acid, myostatin, or interleukin-15 levels. These metabolites were also not associated with changes in lean tissue accumulation.
- The RTC results correlated with the findings of the UK biobank cohort; however, circulating fatty acids showed ambiguous and sex-dependent associations.
IN PRACTICE:
"Overfeeding with SFA or n-6 PUFA for 8 weeks in overweight and obese participants does not differentially affect lean tissue accumulation," the authors commented, saying that the phenomenon of greater lean tissue accumulation in young lean individuals could not be replicated in this population.
SOURCE:
This study was led by Fredrik Rosqvist, Department of Public Health and Caring Sciences, Clinical Nutrition and Metabolism, Uppsala University, Uppsala, Sweden. It was published online in the American Journal of Clinical Nutrition.
LIMITATIONS:
Hypercaloric conditions during the RCT limited the overall generalizability of this study. Metabolite levels were measured in circulation rather than in the skeletal muscles. The study did not include resistance exercise, which warrants further investigation. In the UK Biobank analysis, it was not possible to draw causal inferences owing to the observational nature of this study.
DISCLOSURES:
The trial received funding from the Swedish Research Council, Heart Lung Foundation, Swedish Diabetes Foundation, and other sources. One author declared receiving financial support, serving as an employee, or holding stocks in Antaros Medical.
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