Exercise-induced metabolic improvement not caused by just adipose change

By Sally Robertson, B.Sc.Jun 26 2012

The improvements in metabolic parameters that are achieved with increased physical activity are unlikely to be due to functional changes in adipose tissue alone, report researchers.

Seventy-three overweight-to-obese individuals who aimed to increase their physical activity level to 30 minutes of moderate-intensity exercise per day had several improvements in metabolic parameters after 6 months, but only modest changes in adipose tissue metabolism.

Compared with baseline, the intervention participants (body mass index [BMI] ≥25 kg/m² and <40 kg/m²) increased their mean weekly exercise time by 137 minutes more than the control group did and also had a 1.5 kg and 0.68 kg/m² greater decrease in mean body fat mass (BFM) and BMI, respectively.

Despite these improvements in metabolic parameters, only minor changes in adipose tissue metabolism occurred, report Rachel Fisher (Karolinska Institutet, Stockholm, Sweden) and team in Lipids, Health and Disease.

Mean concentrations of circulating adiponectin were unchanged from baseline, with no between-group differences. However, concentrations of leptin decreased significantly more in the intervention group compared with the control group, by 1.8 ng/mL versus 1.1 ng/mL.

There was also a significantly greater increase in the linoleic fatty acid content of adipose tissue in the intervention compared with the control group, which increased by 0.17% versus 0.02%, respectively. However, the magnitude of change was small, notes the team.

There were no significant between-group differences in changes for any other fatty acid.

The changes in adipose tissue linoleic acid content were not predicted by changes in weight, BMI, BFM, or glycated hemoglobin in either group, but change in exercise time was a significant predictor in the intervention group.

By contrast, the decreases in circulating leptin concentrations were predicted by decreases in weight, BMI and BFM, but not exercise time.

This indicates that the effect of increased physical activity on the linoleic acid content of adipose tissue may have been direct and not mediated via changes in adipose tissue mass or glucose control, writes the team, while the lowering of leptin may have been mediated by decreases in fat mass, rather than by a direct effect of increased physical activity.

Fisher et al say that although their results show that changes in adipose tissue did occur, "these changes were relatively modest and we conclude that improvements in metabolic parameters induced by only a moderate increase in physical activity are unlikely to be driven solely by these changes in adipose tissue metabolism."

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