medwireNews: Researchers have established a dose–response effect of exercise on glucose metabolism in people with type 2 diabetes who are dieting for weight loss.
However, the optimal amount of exercise varied according to the measure used, with a linear relationship observed using a hyperglycemic clamp but not a mixed-meal tolerance test.
The primary outcome was the change in the late-phase disposition index – a measure that accounts for both beta-cell function and insulin sensitivity – during the last 30 minutes of the hyperglycemia clamp.
During the 16 weeks of the study, this reduced more in the 21 participants randomly assigned to undertake diet and a high dose of exercise than in any of the other groups.
These people received a standard dietary intervention and undertook six aerobic training sessions/week, two of which also contained resistance training, aiming for a total 300–330 minutes of exercise per week.
The other groups comprised standard care (n=20; controls), standard dietary intervention (n=21), and dietary intervention plus moderate-dose exercise (n=20; 150–165 minutes/week). There was a significant linear dose–response relationship across these groups.
“This seemed to be achieved by additional increases in insulin sensitivity induced by exercise in a dose-dependent manner,” say Mathias Ried-Larsen (University of Southern Denmark, Odense) and study co-authors.
Insulin secretion, on the other hand, significantly increased in all groups receiving the dietary intervention versus the controls, but exercise did not add to this effect.
“Therefore, it could be speculated that diet-induced weight loss alone might explain this observation and that a weight loss of ~7.5% body weight may be sufficient to re-establish late-phase [insulin secretion] in this study population,” writes the team.
Average weight loss was 0.3 kg in the control group, 7.4 kg in the diet group, and 10.6 and 11.9 kg in the moderate- and high-dose exercise groups, respectively. The study participants all had type 2 diabetes of less than 7 years’ duration and were not taking insulin.
When looking at the same glucose metabolism indices determined from a mixed-meal tolerance test, the researchers found “diminished returns” for high- versus low-dose exercise for the disposition index and insulin sensitivity index and no effect of any intervention on insulin secretion.
“Hence, data from the meal stimulation suggest that increasing the exercise dose beyond three times per week may be redundant to gain additional benefits of exercise on beta-cell function when performed in conjunction with diet-induced weight loss,” they write in Nature Metabolism.
They add: “Likewise, although weight loss was larger in both exercise groups compared with diet-induced weight loss alone, there was no apparent additional weight loss when doubling the exercise volume from three to six sessions per week.”
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