Resistance exercise helps reduce obesity risk

Individuals who do resistance exercise (RE) have a significantly lower risk of developing obesity regardless of whether one meets the aerobic exercise (AE) guidelines, suggests a study. However, those who meet both the RE and AE guidelines show the lowest risk of obesity.

“While it is still not clear if RE alone is sufficient to reduce the risk of developing obesity at the population level, these results clearly suggest that performing both RE and AE may be the best approach to prevent obesity,” the researchers said.

The study included 11,938 healthy adults aged 18–89 years with a body mass index (BMI) <30 kg/m² at baseline who completed at least two clinical examinations during 1987–2005 as part of the Aerobics Center Longitudinal Study. A standardized questionnaire was used to collect self-reported RE participation in min/week and days/week.

Incident obesity was defined as a BMI ≥30 kg/m² at follow-up, as well as by waist circumference (WC) >102/88 cm and percent body fat (PBF) ≥25 percent/30 percent for men/women, respectively, in participants who were not obese by WC (n=9,490) or PBF (n=8,733) at baseline.

A total of 874 (7 percent), 726 (8 percent), and 1,683 (19 percent) developed obesity defined by BMI, WC, or PBF, respectively, over a mean follow-up of 6 years. [PLoS Med 2021;18:e1003687]

RE for 60–119 min/week vs no RE correlated with 30-, 41-, and 31-percent reduced risk of obesity defined by BMI (hazard ratio [HR], 0.70, 95 percent confidence interval [CI], 0.54–0.92; p=0.008), WC (HR, 0.59, 95 percent CI, 0.44–0.81; p<0.001), and PBF (HR, 0.69, 95 percent CI, 0.57–0.83; p<0.001), respectively, after adjusting for confounders such as age, sex, examination year, smoking status, heavy alcohol consumption, hypertension, hypercholesterolaemia, diabetes, and AE.

Meeting the RE guidelines also correlated with 18-, 30-, and 30-percent lower risk of obesity defined by BMI (HR, 0.82, 95 percent CI, 0.69–0.97; p=0.02), WC (HR, 0.70, 95 percent CI, 0.57–0.85; p<0.001), and PBF (HR, 0.70, 95 percent CI, 0.62–0.79; p<0.001), respectively, compared with not meeting the RE guidelines. However, meeting both the AE and RE guidelines led to the lowest risk of obesity.

“A unique aspect of this study was the use of multiple adiposity measures, which revealed consistent, but somewhat nuanced, associations between RE and obesity,” the researchers said.

For instance, high amounts of RE did not correspond to a reduced risk of obesity defined by BMI, but the same high amounts of RE significantly correlated with a lower risk of obesity defined by WC or PBF.

“Thus, it is possible that individuals regularly performing high amounts of RE and possibly increasing their muscle mass may be classified as obese according to BMI, which does not take into account fat distribution and body composition, as WC and PBF do,” the researchers noted.

The dose–response relationship between RE and obesity were most pronounced for PBF, stressing the protective effect of RE against “excessive fat accumulation, which is the physiological definition of obesity that may be most strongly associated with adverse clinical outcomes.” [BMJ 2018;362:k2575; Ann Intern Med 2016;164:532-541; JAMA Netw Open 2019;2:e197337]

Some mechanisms may help explain how RE helps prevent obesity. First, RE increases basal metabolic rate, which constitutes the largest portion of daily caloric expenditure. Second, doing RE requires increased caloric expenditures, but not to the same magnitude as an AE. [J Sports Sci 2020;38:1635-1649; Med Sci Sports Exerc 2001;33:532-541; Med Sci Sports Exerc 2011;43:1575-1581]

“Furthermore, RE may stimulate muscle hypertrophy, which has been found to cause reductions in fat mass, potentially due to increases in glycolysis and fat oxidation throughout the body,” the researchers said. “This may explain why the associations between RE and obesity were weaker using BMI as the outcome.” [Cell Metab 2008;7:159-172; Int J Biol Sci 2016;12:617-630]

The current study was limited by its participants being mostly White men from middle to upper socioeconomic strata, use of self-reported RE, and lack of detailed diet data.