High blood sugar can block the VO2max benefits of exercise — a keto diet reversed it in mice

VO2max — how efficiently your body uses oxygen during exercise — is one of the most reliable predictors of long-term health we have, and it typically improves with regular aerobic training. A 2026 Virginia Tech study highlights an important exception: elevated blood sugar appears to blunt that improvement, and a high-fat ketogenic diet reversed the block in mice.

The problem the study addressed

People with elevated blood sugar (hyperglycemia) often see smaller-than-expected improvements in oxygen-uptake efficiency from exercise, even when they train consistently. Since VO2max gains are one of exercise’s biggest long-term payoffs, this means a chunk of the population training hard may be missing out on one of its most protective effects.

What the researchers did

Sarah Lessard’s team at the Fralin Biomedical Research Institute fed hyperglycemic mice a high-fat, low-carbohydrate ketogenic diet while they ran regularly on exercise wheels. Within one week, blood sugar normalized completely. Over time, the mice’s muscles remodeled toward more slow-twitch, oxidative fibers — the type associated with endurance — and became measurably better at using oxygen during exercise.

"After one week on the ketogenic diet, their blood sugar was completely normal, as though they didn’t have diabetes at all. Over time, the diet caused remodeling of the mice’s muscles, making them more oxidative and making them react better to aerobic exercise." — Sarah Lessard, lead researcher

The bigger point: diet and exercise interact, not just add up

Lessard frames the finding as evidence that diet and exercise are not simply two separate levers you pull independently — how you eat can determine how much benefit a given training stimulus actually delivers. She is careful to note the ketogenic diet is difficult for many people to sustain, and that a less restrictive approach such as a Mediterranean-style diet may achieve similar blood-sugar benefits while being easier to maintain long-term.

What this means before human trials confirm it

This is mouse data, and human follow-up (which Lessard says is planned) is needed before drawing firm dietary prescriptions. But the underlying principle — that unmanaged blood sugar can quietly cap your return on training effort — is well supported elsewhere in the human literature, and is a reasonable argument for treating glucose control as part of your training plan, not a separate concern.

This is exactly why Misi pairs its Zone 2 and VO2max training targets with your logged glucose and HbA1c trends from labs — so a plateau in cardio fitness can be checked against blood sugar control rather than assumed to be a training-volume problem alone.