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A new study from the University of Campinas (UNICAMP) in São Paulo State, Brazil, shows that physical exercise such as weight training can help control diabetes in obese people even before weight loss occurs. The study, conducted on mice, found that working out reduced accumulated liver fat and improved blood sugar control.
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Working out the hows and whys
"Everyone knows physical exercise helps control disease. Our research focuses on how and why this is so, on the mechanisms involved. If we can discover a key protein whose levels rise or fall with training, we'll have taken a step toward the development of drugs that mimic some of the benefits of physical exercise," said Leandro Pereira de Moura, a professor at UNICAMP's School of Applied Sciences and the principal investigator of the study.
To study the effect of weight training on the liver, the researchers experimented on three groups of mice. There was a control group, which was fed a standard diet (4% fat) and second and third groups, which were fed a hyperlipidemic diet (35% fat) for 14 weeks.
The first group and second groups remained sedentary while the third group was put through a moderate strength training exercise. The exercise saw the mice climb a staircase with a weight attached to their tail.
"Before we began the experiment, we conducted tests to determine the maximum load each animal could bear. We used a weight corresponding to 70% of this limit in the exercise sessions. Our group had previously shown overtraining can contribute significantly to the development of nonalcoholic fatty liver disease. Excessively strenuous exercise can do more harm than good," Moura said.
Exercise protocol of only 15 days
The researchers decided to study a short exercise protocol of only 15 days. This was done to ensure that the benefits observed were directly linked to strength training and not to the secondary effects of weight loss.
Surprisingly, the researchers found that although the mice exercising were still obese at the end of the 15-day period, their fasting blood sugar levels were normal. Furthermore, to analyze the effect of exercise on the control of hepatic gluconeogenesis, the researchers tested the animals for tolerance of pyruvate.
"The test consisted basically of administering pyruvate to the mice and measuring the amount of glucose produced by the liver," Moura explained.
"We found that the trained mice produced less glucose than the sedentary obese mice even though they received the same amount of substrate. This showed that the trained animal's liver underwent metabolic alterations that made it more sensitive to insulin."
Next, the researchers investigated the mechanism by which exercise reduced liver fat. "We compared the sedentary obese mice with the exercised mice by means of gene and protein analyses to evaluate the synthesis and oxidation of liver fat," Moura said.
"We observed a tendency towards more liver fat accumulation in the sedentary mice."
The results of the study are published in the Journal of Endocrinology.