Ketogenic Diet Restores Exercise Benefits Lost to High Blood Sugar in Mice

A new study reports that, in mice, a ketogenic diet restored an important training benefit that high blood sugar had switched off: exercise was once again able to increase oxygen use.

The finding reframes exercise resistance, indicating that metabolic control may determine whether endurance training can deliver its full effects.

Where benefits stall

The paper found that aerobic training failed to generate its normal increase in oxygen use in mice with high blood sugar.

Sarah J. Lessard of Virginia Tech’s Fralin Biomedical Research Institute traced this failure and found that a ketogenic diet normalised blood sugar within a week.

After glucose levels dropped, the animals’ muscles once more acquired the endurance-focused characteristics that routine training had previously been unable to produce.

The findings identify a boundary to what exercise alone can achieve and raise the deeper issue of why metabolism may decide whether training performs as expected.

The role of oxygen use

In exercise science, VO2peak-the greatest rate at which oxygen can be used-indicates how effectively the body can maintain demanding activity.

Human research consistently links better cardiorespiratory fitness with reduced risks of premature death and chronic illness.

A review in people with diabetes found that lower aerobic capacity is also associated with more cardiovascular complications and worse physical function.

This helps show how high blood sugar may quietly reduce the returns from exercise, even for someone who trains regularly.

Fat becomes fuel

When carbohydrate consumption falls to a very low level, ketosis takes over fuel use, meaning that the body primarily burns fat.

For the mice, this resulted in greater fat burning at rest and during activity, while glucose use and storage decreased.

As fat requires more oxygen than carbohydrate to produce energy, oxygen consumption increased before fitness itself improved.

This distinction is important: increased oxygen use on its own did not mean that the diet automatically enhanced performance.

Muscles adapt to keto

Within the muscles, the ketogenic diet reduced proteins responsible for drawing glucose into cells and increased those involved in transporting fatty acids.

Meanwhile, mitochondria-the structures that convert fuel into usable energy-grew both larger and more numerous.

These alterations help account for the animals’ reliance on fat and their apparent preparation for endurance activity.

However, this metabolic rewiring mattered most when exercise provided the signal directing muscle to build its next adaptations.

Vessels grow back

With training, capillaries-the smallest blood vessels in muscle-increased in ketogenic mice, whereas they changed very little in mice fed regular chow.

A greater number of capillaries provides more pathways for oxygen to reach muscle, improving aerobic capacity as exercise intensity rises.

“Over time, the diet caused remodeling of the mice’s muscles, making them more oxidative and making them react better to aerobic exercise,” said Lessard.

Together, these effects reinstated the muscle adaptations that high blood sugar had prevented, connecting improved glucose control with better oxygen delivery.

Performance did not rise

Despite their improved oxygen use, ketogenic mice did not endure maximal treadmill tests for longer than chow-fed mice.

“Their bodies were more efficiently using oxygen, which is a sign of higher aerobic capacity,” said Lessard.

A likely explanation was reduced glycogen, the stored carbohydrate held in muscle and liver, which dropped to half the level seen with chow.

After long-term keto feeding, researchers reintroduced carbohydrates for one week; treadmill performance then improved, even as ketone levels fell.

Normal sugar differs

The ketogenic diet did not improve the training response in the same way among mice whose blood sugar was normal at the outset.

Sedentary animals experienced some increase in aerobic capacity, but animals trained through exercise gained no additional training advantage from keto.

This difference indicates that lowering glucose accounted for most of the effect in the high-blood-sugar mice, rather than fat burning alone.

It also cautions against assuming that a diet helpful in one metabolic condition will benefit every condition to the same extent.

What humans face

As the experiment involved male mice with induced diabetes, it should not be interpreted as a ready-to-use plan for humans.

Beyond disease settings, sports nutrition experts say ketogenic diets are generally neutral or detrimental to athletic performance.

“Our previous studies have shown that any strategy you and your doctor have arrived at to reduce your blood sugar could work,” said Lessard.

That allows for Mediterranean-style eating supported by a guideline, although any practical plan still requires medical advice.

Next phase of study

Human trials must now establish whether reducing blood sugar before and during training can restore this lost exercise benefit in people.

Researchers will also have to distinguish between two potential causes: lower glucose itself and elevated ketones during exercise.

Earlier evidence in humans suggests that the issue is clinically plausible rather than merely an unusual feature of mice.

That makes the mouse finding more than a curiosity, as it presents a mechanism that warrants testing in clinical research.

What this changes

Exercise remains beneficial, but this research suggests muscles respond most effectively when training and metabolism are no longer working against one another.

For people with persistently high blood sugar, the next practical question is which diet can make exercise effective again.