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.