Health & Fitness | August 3, 2020 12:40 pm

Study: Workouts Can’t Do Their Job If You Eat Too Much Sugar

Rewarding yourself with a donut after exercise is counterproductive

Athlete in the gym holding battle ropes
Are you working out to justify sugary snacks? That might be a problem.
Meghan Holmes/Unsplash

According to a study published this month in Nature Metabolism, elevated blood sugar levels in human beings can impair muscle signaling and ultimately sabotage workouts. After decades of an established, common-sense understanding that hyperglycemia (an excess of glucose in the bloodstream) was related to poor aerobic fitness, and an increased risk for heart disease, Type 2 diabetes and lowered life expectancy, the recent report detailed the exact biological association between consuming lots of sugar, and gleaning less rewards from exercise.

Researchers at Boston’s Joslin Diabetes Center put a bunch of mice on the modern Western diet — lots of sugar, lots of saturated fat — and then injected them with an insulin-production inhibitor, meant to simulate the processes that occur in human bodies battling diabetes, as The New York Times detailed. These mice, now fat and incapable of controlling their blood sugar, were given cages and running wheels and observed for six weeks. Alongside a control group of “normal” mice, the mice with high blood sugar ran quite a bit: about 300 miles. But despite that fact (and in contrast to the other mice), they struggled to make any progress in their aerobic fitness.

When the scientists looked within the muscles of the “unhealthy” mice, they discovered deposits of collagen, which had prevented the development of new muscle fibers. They spotted something similar in humans exercising with elevated blood sugar: stiff proteins buried deep in the muscle tissue, preventing the flow of oxygen (and the general improvement of aerobic fitness). The researchers concluded: “constantly bathing your tissues in sugar is just not a good idea.”

It’s a cautionary tale for a common refrain: “Exercise more so I can eat more.” If that uptick in consumption involves lots of sugar, especially processed products with added sugar, it could largely erase your efforts on the roads or in the gym. Which is a true shame. Next time you get your sweat on, consider that spot of exercise to be reward enough — the donut could just cancel the whole thing out.

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