Although exercise is essential for good health, high blood glucose levels can reduce or even cancel out the benefits of exercise.
Physical activity is not only good for morale, but also for fitness: many studies have shown the importance of aerobic exercise for overall health.
However, these benefits must be supported by a healthy diet, as they can be greatly reduced in the event of chronic hyperglycemia, i.e. abnormally high blood sugar levels.
This is the result of a study conducted at the Joslin Diabetes Center in Boston and published in Nature Metabolism. According to the authors, who observed this decrease in gains from aerobic exercise in rats and humans, high blood glucose levels have a negative effect on physical fitness. They also found that people with hyperglycemia had below-average physical fitness.
Difficulties in improving physical fitness
To reach these conclusions, the scientists used two models of mice with high blood sugar levels. The first group of rats was fed a western diet rich in sugar and saturated fatty acids, which led to some weight gain in addition to the high blood sugar levels. The other group was genetically modified to produce less insulin, which resulted in a similar increase in blood sugar as with the Western diet, although the rats followed a diet that was less rich in sugar and fat and maintained normal body weight. Both groups then underwent a training protocol in which they ran on wheels in their cages to improve their aerobic condition.
In total, the rodents ran about 500 kilometers during the study but were unable to improve their aerobic exercise capacity compared to non-hyperglycemic mice.
Less well-vascularized muscles
Upon closer examination of the skeletal muscles of these rats, the researchers found that the muscle tissue was less vascularized, which explains why the level of aerobic fitness did not increase. The authors of the study, therefore, concluded that high blood sugar levels could prevent muscle remodeling.
This conclusion was confirmed in clinical tests on young adults. Volunteers who had higher blood glucose levels after glucose intake also showed a lower capacity for aerobic exercise.
“The good news is that although our hyperglycemic mouse models did not improve aerobic fitness through exercise, they did achieve other important health benefits from exercise, including a reduction in body fat and improved glucose metabolism,” said Sarah Lessard, lead author of the study. Therefore, regular aerobic exercise remains a key recommendation for maintaining the health of people with and without high blood sugar levels.
In her opinion, these results show that it is possible for people with chronic hyperglycemia to increase their ability to engage in aerobic exercise, particularly through a low blood glucose diet or by taking specially designed antidiabetic drugs to keep blood glucose levels within normal limits. “We often see diet and exercise as separate ways to improve our health,” says Lessard. But our research shows that there are more interactions between these two lifestyle factors than we have ever known, and suggests that we should look at them together to maximize the health benefits of aerobic exercise.