Exercise is one of the strongest predictors of long-term health. It strengthens the heart, improves endurance and helps regulate blood sugar. But when blood sugar remains chronically high, those benefits may not fully show up.
A new study published in Nature Communications suggests that elevated blood sugar may blunt how muscles respond to aerobic training. In hyperglycemic mice, researchers found that a ketogenic diet lowered blood sugar and enhanced the animals’ response to exercise.
The study was led by Sarah Lessard, an associate professor at Virginia Tech’s Fralin Biomedical Research Institute. Her team fed male mice a high-fat, very low-carbohydrate ketogenic diet while allowing them to exercise.
Within one week, blood sugar levels normalized.
“After one week on the ketogenic diet, their blood sugar was completely normal, as though they didn't have diabetes at all,” Lessard said.
The researchers then looked at how the mice’s muscles adapted to training. Mice on the ketogenic diet developed more slow-twitch muscle fibers, which support endurance, and showed changes in their mitochondria, the structures inside cells that help produce energy.
“Their bodies were more efficiently using oxygen, which is a sign of higher aerobic capacity,” Lessard said.
Aerobic capacity is closely linked to longevity and overall health. In earlier research, Lessard’s team had found that people with high blood sugar tend to have lower exercise capacity. This new study suggests that blood sugar itself may interfere with how muscles adapt to exercise.
Still, the findings come from an animal model. Mice are not humans, and metabolic responses can differ. The study does not prove that a ketogenic diet will restore exercise benefits in people with diabetes or prediabetes.
Lessard also emphasized that the interaction between diet and exercise may matter more than any single approach.
“There are a lot of combined effects, and so we can get the most benefits from exercise if we eat a healthy diet at the same time,” she said.
While the ketogenic diet is known for sharply restricting carbohydrates, it can be difficult to maintain and may not be appropriate for everyone. Lessard noted that other dietary strategies that lower blood sugar, including less restrictive patterns such as the Mediterranean diet, may also support exercise response.
The broader takeaway is not that everyone should adopt keto. Rather, the findings suggest that improving blood sugar control, through diet, medication or other physician-guided approaches, may allow the body to respond more fully to exercise.
Human studies will be needed to determine whether the same effects occur outside the laboratory.
This study was supported by the National Institutes of Health, including the National Institute of Diabetes and Digestive and Kidney Disorders, along with additional support from the American Diabetes Association, the Joslin Diabetes Center and international research foundations.