The authors of this study explain that chronic high blood sugar can affect proper adaptation to aerobic exercise. People with high blood sugar may struggle to make improvements in peak oxygen consumption rate, which has to do with the highest level of oxygen the body can use in high-intensity exercise.
Previous research from this group had shown that high blood sugar in mice “impairs aerobic adaptation.” They wanted to see if the ketogenic diet could help restore this in mice that underwent exercise training. The ketogenic diet involves consuming higher amounts of fat and lower amounts of carbohydrates.
To test their ideas, they worked with mice with induced high blood sugar and control mice. Some high-blood-sugar mice received a ketogenic diet, while others received a normal diet. The non-high-blood-sugar controls also received a regular diet.
The researchers monitored the mice’s weight and blood sugar levels. Some mice underwent exercise while others remained sedentary. Researchers further tested how switching back to a regular diet following the ketogenic diet affected outcomes. They also had some sedentary mice complete one exercise bout.
Researchers evaluated the mice after the exercise training period, assessing factors such as blood sugar, maximum exercise capacity, and body composition.
Researchers found that mice with high blood sugar on the ketogenic diet had normal blood sugar levels compared to mice with high blood sugar levels on the normal diet, which was high in carbohydrates. Mice with high blood sugar on the ketogenic diet also had blood ketones, indicating the use of fat as an energy source.
Exercising while on a keto diet vs. not exercising
Regarding exercise training, all mice, regardless of diet or blood sugar levels, experienced benefits such as improved lean mass and lower random blood sugar levels. The sedentary mice on the ketogenic diet gained fat mass and weight.
For the mice who underwent exercise training and were on the ketogenic diet, the ketogenic diet appeared to cancel out the problems with peak oxygen consumption. In contrast, the high-blood-sugar mice doing exercise training and on a normal diet experienced blunted improvements in peak oxygen consumption.
Problems with skeletal muscle remodeling that occurred in the normal diet and high blood sugar mice that were exercising were not observed in the exercise training mice on the ketogenic diet.
The authors note that this fix in skeletal muscle remodeling could be why there were the observed improvements in peak oxygen consumption. Further research also suggested that ketones may help with this muscle remodeling.
However, exercise performance was about the same for these groups. One possible reason is that the ketogenic group had lower levels of glycogen, which is how the body stores carbohydrates.
Mice on the ketogenic diet had higher rates of fatty acid oxidation, which aids in fatty acid breakdown. In the exercising mice on the ketogenic diet, there also appeared to be greater levels of oxygen use “during the first 10 minutes of maximal exercise testing.”
The results suggest that the change in peak oxygen consumption from the keto diet and exercise training is separate from fatty acid oxidation rates. Sedentary ketogenic diet mice also had higher levels of oxygen use and fatty acid oxidation rates during moderate exercise compared to mice on normal diets. They also had altered levels of certain substances like lactate.
In skeletal muscles of mice on the ketogenic diet, glucose metabolism and transport were downregulated, while fatty acid metabolism and transport were upregulated. The authors also observed changes in the skeletal muscles that they believe indicate the muscles adapt in many ways to a ketogenic diet.
These changes may be the underlying reason they also observed increased fatty acid oxidation. They also observed changes in muscle
Researchers followed up by seeing how the ketogenic diet and exercise affect mice with normal blood sugar levels.
One notable finding was that the ketogenic diet did help improve peak oxygen consumption rate in sedentary, but not in exercise-training mice. In these mice, researchers found that switching back to carbohydrates for one week from the ketogenic diet enhanced exercise performance, helping to mitigate “the disconnect between VO2peak and exercise performance in KETO-fed mice.”
Study author Sarah Lessard, PhD, Associate Professor, Fralin Biomedical Research Institute, Center for Exercise Medicine Research, explained the following to Medical News Today:
“When combined with exercise training, a keto diet can improve the health benefits gained from exercise in mice. Specifically, mice with hyperglycemia that consumed a ketogenic diet had bigger improvements in aerobic exercise capacity (a measure of the body’s ability to use oxygen) than mice consuming a regular diet with high carbohydrate content.”
“We think the exercise improvements with a ketogenic diet are due to the blood glucose-lowering properties of the diet, as high blood glucose appears to ‘block’ some of the positive benefits of exercise,” she said.
The major limitation of this study is the use of animals, specifically male mice, which doesn’t directly translate to work with people. Researchers also used cell research, which also doesn’t directly apply to people.
High blood sugar was also something induced in mice in this study, so it’s certainly not the same as how diabetes develops in people. The ketogenic diet in mice was also different from what it may look like in people.
The authors further note that they did not measure how mice’s diets affected fasting ketone levels or post-glucose-load insulin levels, which could have provided useful information. Caloric intake tended to be higher in the mice on the ketogenic diet, though exercise appeared to offset this.
It is also possible that fat mass could have impacted the results of the peak oxygen consumption.
Future research can explore the effects of the ketogenic diet along with exercise in people with high blood sugar and confirm underlying mechanisms.
While this study was only conducted in mice and indicates the need for more research, it does suggest possible benefits in people with diabetes from following a ketogenic diet and exercising. Lessard noted the following to Medical News Today:
“People with high blood sugar due to diabetes or insulin resistance may not gain the same health benefits from exercise as those with normal blood sugar levels.”
“Our work shows that diets or other treatments that can lower blood sugar in those with hyperglycemia may help to enhance the response to exercise training, leading to improved aerobic exercise capacity. This is important, because low aerobic exercise capacity is a strong risk factor for chronic disease and mortality,” Lessard said.
However, caution may be warranted regarding the ketogenic diet. Karen Z. Berg, MS, RD, CDN, who was not involved in the study, explained the following:
“A ketogenic diet is a diet that is high in both protein and fat and avoids or limits carbohydrates. Unfortunately, many people who have hyperglycemia or Type 2 [diabetes mellitus] also suffer from other co-morbidities that would not benefit at all from a keto diet. Oftentimes, Type 2 diabetes is accompanied by obesity and/or heart disease. A high fat diet is the opposite of what these individuals need.”
That being said, the ketogenic diet may work for some individuals. Kristin Kirkpatrick, MS, RDN, who was also not involved in the study, noted the following:
“We always have to interpret keto research in a real-world context. In my clinical practice, I’ve seen meaningful benefits with both ketogenic and lower-carbohydrate approaches — with ‘lower carb’ generally around 25% of total calories.”
“But one of the biggest questions [with a ketogenic diet] is sustainability. The long-term success of any dietary pattern ultimately depends on whether someone can realistically maintain it over time.”
— Kristin Kirkpatrick, MS, RDN
