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It’s long been known that eating sugary treats and processed foods undermines our health. But new research details how high blood-sugar levels can also block our bodies’ response to exercise.

In tests with mice and with human participants, researchers found that those diagnosed with hyperglycemia may reap fewer benefits from exercise. Excessive blood sugar impairs muscle signaling and aerobic adaptation to exercise, according to lead senior author Sarah Lessard, MSc, PhD, at the Joslin Diabetes Center and Harvard Medical School.

One group of mice was fed a diet rich in sugar and saturated fat; they quickly developed high blood-sugar levels and gained weight. Another group ate normal food, but they were injected with a substance that reduces insulin production; they didn’t put on fat, but blood-sugar levels rose to levels similar to those of the first group. A control group ate normal food.

After two months, all the mice were allowed to jog at will on running wheels over six weeks. They all ran about the same amount of time but exhibited dramatically different fitness results. The control group was much fitter as a result of the exercise. Mice with high blood-sugar levels — either from food or from injections — showed little improvement.

Examining the mice showed why: The control group’s muscles were full of healthy new blood vessels, and their muscle fibers had gained the characteristics of an endurance athlete’s. The others’ were pocked with deposits of collagen proteins that seem to have impaired the production of new blood vessels and changes to their muscle fibers, preventing the mice from adapting to the exercise.

Although more research in humans is needed, the research is a good reminder to limit sugar in our daily diets.

Michael Dregni

Michael Dregni is an Experience Life deputy editor.

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