How the Ketogenic Diet Impacts High Blood Sugar
Chronically elevated blood sugar levels can hinder the body’s ability to adapt to aerobic exercise, according to researchers. Individuals with hyperglycemia may struggle to improve their maximal oxygen consumption rate – a key indicator of cardiovascular fitness and the body’s ability to utilize oxygen during intense activity.
Previous research from the same team demonstrated that high blood sugar in mice “impairs aerobic adaptation.” They aimed to determine if a ketogenic diet could help restore this function in mice undergoing physical training. A ketogenic diet involves significantly increasing fat intake although reducing carbohydrate consumption.
To investigate this, researchers worked with mice exhibiting high blood sugar and a control group. Some of the mice with elevated blood sugar were placed on a ketogenic diet, while others continued with a standard diet. The control group, which did not have hyperglycemia, also received a regular diet.
The researchers monitored the mice’s weight and blood sugar levels. Some mice were given the opportunity to exercise, while others remained sedentary. They further tested how returning to a standard diet after the ketogenic diet affected the outcomes, and also assessed the impact of introducing exercise to the sedentary mice.
Following the exercise period, researchers evaluated the mice, assessing factors such as blood sugar, maximal exercise capacity, and body composition.
The study found that mice with high blood sugar who followed a ketogenic diet had normalized blood sugar levels compared to those with high blood sugar on a standard, carbohydrate-rich diet. The mice on the ketogenic diet also exhibited blood ketones, indicating the body was utilizing fat as a primary energy source.
Exercise During a Keto Diet, or Not?
Regarding physical training, all mice – regardless of diet or blood sugar levels – experienced benefits such as improved lean mass and reduced blood sugar. However, the sedentary mice on the ketogenic diet gained fat mass and weight.
For the mice that exercised while following a ketogenic diet, the diet appeared to counteract the issues with maximal oxygen consumption. In contrast, mice with high blood sugar who exercised while on a standard diet experienced only moderate improvements in their maximal oxygen consumption.
Problems with skeletal muscle remodeling, observed in mice on a standard diet with hyperglycemia who exercised, were not seen in the mice trained on the ketogenic diet. This finding is significant, as skeletal muscle health is crucial for overall metabolic function.
The authors note that this difficulty in skeletal muscle remodeling could explain the observed improvements in maximal oxygen consumption, and further research suggests ketones may contribute to this muscle remodeling process.
However, physical performance was roughly equivalent between these groups. One potential reason for this is that the ketogenic group had lower levels of glycogen, the body’s stored form of carbohydrates.
Mice on the ketogenic diet showed higher rates of fatty acid oxidation, meaning they were more efficient at breaking down fats for energy. In the mice that exercised while on a ketogenic diet, there also appeared to be higher oxygen consumption levels “during the first 10 minutes of maximal exertion.”
The results suggest that the changes in maximal oxygen consumption resulting from the keto diet and exercise are distinct from fatty acid oxidation rates. Sedentary mice on a ketogenic diet also demonstrated higher oxygen consumption levels and fatty acid oxidation rates during moderate exercise compared to those on a standard diet, and also exhibited altered levels of certain substances like lactate.
In the skeletal muscles of mice on a ketogenic diet, glucose metabolism and transport were down-regulated, while fatty acid metabolism and transport were up-regulated. Researchers also observed changes in the skeletal muscles that they believe indicate the muscles were adapting in multiple ways to the ketogenic diet.
These changes may underlie the increased fatty acid oxidation observed. They also noted changes in the muscles’
Researchers then examined how the ketogenic diet and exercise affected mice with normal blood sugar levels.
Notably, the ketogenic diet did improve the rate of maximal oxygen consumption in sedentary mice, but not in the mice undergoing exercise training. In these mice, returning to carbohydrates for one week after the ketogenic diet improved physical performance, helping to mitigate “the mismatch between peak VO2 and physical performance in KETO-fed mice.”
Study author Sarah Lessard, PhD, an associate professor at the Fralin Biomedical Research Institute, Center for Exercise Medicine Research, explained to Medical News Today:
“When paired with physical training, a keto diet can enhance the health benefits of exercise in mice. Specifically, mice with hyperglycemia who followed a ketogenic diet showed greater improvements in their aerobic exercise capacity (a measure of the body’s ability to use oxygen) than mice consuming a high-carbohydrate regular diet.”
“We believe the improvements in exercise with the keto diet are due to the blood sugar-lowering properties of the diet, as high blood sugar appears to ‘block’ some of the positive benefits of exercise,” she said.
Why More Research is Needed on This Topic
The primary limitation of this study is its use of animals, specifically male mice, which doesn’t directly translate to human outcomes. Researchers also utilized cell-based research, which isn’t directly applicable to humans either.
Hyperglycemia was also induced in the mice in this study, which is not the same as how diabetes develops in humans. The ketogenic diet used in the mice was also different from what it might look like in a human.
The authors further note that they did not measure the impact of the mice’s diet on ketone levels during fasting or on insulin levels after a glucose load, which could have provided valuable insights. Caloric intake tended to be higher in the mice following a ketogenic diet, while exercise appeared to offset this.
It’s also possible that fat mass impacted the results of maximal oxygen consumption.
Future research could explore the effects of a ketogenic diet combined with exercise in individuals with hyperglycemia and confirm the underlying mechanisms. This research could help refine dietary recommendations for people managing blood sugar and seeking to improve their fitness.
While this study was conducted solely on mice and indicates the need for further research, it suggests potential benefits for people with diabetes who follow a ketogenic diet and exercise. Lessard noted to Medical News Today:
“Individuals with hyperglycemia due to diabetes or insulin resistance may not experience the same health benefits from exercise as those with normal blood sugar.”
“Our work shows that diets, or other treatments, that can lower blood sugar in people with hyperglycemia may help improve the response to physical training, leading to improved aerobic exercise capacity. This is important, as low aerobic exercise capacity is a significant risk factor for chronic disease and mortality,” Lessard said.
Why a Ketogenic Diet May Not Be Right for Everyone
However, some caution may be warranted regarding the ketogenic diet. Karen Z. Berg, MS, RD, CDN, who was not involved in the study, explained:
“A ketogenic diet is a high-protein, high-fat diet that avoids or limits carbohydrates. Unfortunately, many people with hyperglycemia or type 2 (diabetes mellitus) also suffer from other comorbidities that would not benefit at all from a keto diet. Often, type 2 diabetes is accompanied by obesity and/or heart disease. A high-fat diet is the opposite of what these individuals need.”
That said, the ketogenic diet can work for some people. Kristin Kirkpatrick, MS, RDN, who also did not participate in the study, noted:
“We always need to interpret research on keto in real-world context. In my clinical practice, I’ve seen significant benefits with both ketogenic and low-carbohydrate approaches – with ‘low 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 diet ultimately depends on a person’s ability to realistically maintain it over time.”
— Kristin Kirkpatrick, MS, RDN
