Study finds ketogenic diet improves blood sugar and exercise response in mice — Evidence Review

A new study in mice suggests that a high-fat ketogenic diet can rapidly normalize blood sugar and improve exercise-related muscle adaptations, including oxygen use. Related research is mixed: while some studies support the metabolic benefits of ketogenic diets, others highlight potential drawbacks or variable effects on exercise performance and glucose regulation (1 2 3 6 7 10).

• Several human and animal studies find that ketogenic diets can improve aerobic performance, lower blood glucose, and alter body composition, but the effects on high-intensity exercise and long-term metabolic health are inconsistent (1 4 7 8).
• Some research indicates that ketogenic diets may cause hepatic insulin resistance and glucose intolerance in the short term, especially depending on fat source and proportion, suggesting that metabolic effects can vary widely (6 10).
• Combining exercise with dietary interventions, regardless of the specific diet, is generally more effective for improving weight loss, fat mass, and metabolic markers than diet alone (11 12 14 15).

Study Overview and Key Findings

Interest in ketogenic diets has surged amid ongoing debates about their health benefits and risks, particularly for individuals with metabolic disorders such as diabetes. The new study, led by Sarah Lessard’s team at the Fralin Biomedical Research Institute at VTC, explores whether a high-fat, low-carbohydrate ketogenic diet can help restore exercise responsiveness in the context of elevated blood sugar—a group that often sees less benefit from physical activity. Notably, the research also investigates muscle remodeling and oxygen utilization, which are key predictors of long-term health.

Property	Value
Study Year	2023
Organization	Fralin Biomedical Research Institute at VTC Center for Exercise Medicine Research, Virginia Tech
Journal Name	Nature Communications
Authors	Sarah Lessard
Population	Mice
Methods	Animal Study
Outcome	Blood sugar levels, muscle oxidative capacity, exercise response
Results	Mice on a ketogenic diet had normal blood sugar after one week.

Literature Review: Related Studies

To contextualize the new findings, we searched the Consensus database, comprising over 200 million research papers, using the following queries:

1. ketogenic diet exercise performance
2. blood sugar levels ketogenic mice
3. exercise effects diet comparisons

Topic	Key Findings
How do ketogenic diets affect exercise metabolism and performance?	- Ketogenic diets can increase fat oxidation and in some cases improve submaximal aerobic performance, but may reduce exercise efficiency and high-intensity performance in trained athletes (1 2 3 5). - Moderate-intensity exercise is generally maintained, but performance at intensities above 70% VO2max may decline due to decreased exercise economy (2 3 5).
What are the effects of ketogenic and low-carbohydrate diets on blood glucose and insulin sensitivity?	- Both ketogenic and low-carbohydrate diets can lower blood glucose and improve insulin sensitivity in mice and humans, but some studies report increased hepatic insulin resistance and glucose intolerance with ketogenic diets, especially short-term or with certain fat sources (6 7 8 10). - Exogenous ketones and ketogenic diets reduce blood glucose in rodent models, with effects observed in both healthy and pathological states (8 9).
How does combining diet and exercise influence metabolic health and weight loss?	- Combined diet and exercise interventions consistently lead to greater weight loss, fat loss, and improvements in cardiovascular and metabolic health than diet or exercise alone (11 12 14 15). - Exercise, especially when paired with dietary changes, has a disproportionately positive effect on reducing visceral adiposity and enhancing long-term outcomes (13 14).
Are there potential risks or limitations to ketogenic diets, particularly concerning glucose metabolism?	- Some animal studies report that ketogenic diets can induce hepatic insulin resistance, glucose intolerance, and lipid accumulation, with effects varying by fat source and diet composition (6 10). - The long-term impact on muscle glycogen restoration and the implications for high-intensity exercise or metabolic health remain unclear and may vary between individuals (5 6 10).

How do ketogenic diets affect exercise metabolism and performance?

The new mouse study’s findings that a ketogenic diet improves muscle oxidative capacity and exercise response align with some human and animal studies showing enhanced aerobic metabolism and fat oxidation. However, several studies note that while moderate exercise performance is preserved or improved, exercise efficiency at higher intensities can suffer, and individual responses may vary.

• Ketogenic diets may increase maximal oxygen uptake (VO2max) and fat oxidation during aerobic exercise, but may simultaneously reduce exercise economy and maximal workload at high intensities (1 2 3).
• Endurance athletes tend to maintain moderate-to-vigorous intensity exercise after keto-adaptation, but may experience declines in efficiency and performance above 70% VO2max (2 3 5).
• Some short-duration, high-intensity performance measures can improve or remain unaffected, but these benefits may be confounded by weight loss rather than direct metabolic effects (3).
• The new mouse study’s focus on improved oxygen utilization and muscle remodeling is consistent with observed increases in oxidative muscle fibers in some endurance athlete studies (1 3).

What are the effects of ketogenic and low-carbohydrate diets on blood glucose and insulin sensitivity?

The rapid normalization of blood sugar in mice on a ketogenic diet echoes findings from both animal and human studies, which generally show lowered blood glucose and increased insulin sensitivity. However, research also points to potential complications, including hepatic insulin resistance and glucose intolerance, particularly in the short term or with certain dietary fat sources.

• Both ketogenic and less-restrictive low-carbohydrate diets reduce blood glucose and improve glucose tolerance and insulin sensitivity in animal models of diabetes (7).
• Short-term ketogenic diets may induce hepatic insulin resistance and decreased glucose tolerance, suggesting a complex interplay between fat intake, carbohydrate restriction, and glucose metabolism (6 10).
• Exogenous ketones have been shown to lower blood glucose in exercised and non-exercised rodent models, supporting some of the metabolic effects seen in the new study (8).
• The source and proportion of dietary fat can significantly influence metabolic outcomes, with some ketogenic diets leading to increased lipid accumulation or altered gut microbiota (10).

How does combining diet and exercise influence metabolic health and weight loss?

The new study’s suggestion that diet and exercise together yield the greatest health improvements is strongly supported by meta-analyses and clinical trials. Evidence consistently shows that combining dietary interventions with regular exercise produces more substantial and sustained health benefits than either strategy alone.

• Meta-analyses demonstrate that diet-plus-exercise interventions result in greater long-term weight loss and improvements in body composition compared to diet alone (11 12 14 15).
• Exercise plays a key role in reducing visceral adiposity, even in the absence of significant weight loss, making it a critical component of metabolic health strategies (13 14).
• Combined interventions also yield better outcomes for cardiovascular risk factors, blood lipids, and blood pressure (14).
• The new study’s emphasis on muscle adaptation and oxygen use aligns with findings that exercise enhances metabolic flexibility and tissue-specific benefits beyond weight loss (13 14).

Are there potential risks or limitations to ketogenic diets, particularly concerning glucose metabolism?

While the new study highlights rapid improvements in blood sugar and exercise response, related research urges caution about possible adverse effects of ketogenic diets, especially concerning hepatic insulin resistance, glucose intolerance, and long-term metabolic outcomes. The variability in outcomes underscores the need for personalized and carefully monitored approaches.

• Short-term ketogenic diets in mice may lead to greater hepatic insulin resistance and impaired glucose homeostasis compared to high-fat diets with more carbohydrates (6 10).
• Alterations in gut microbiota and increased hepatic lipid content can accompany ketogenic diets, potentially increasing the risk of metabolic disorders in some individuals (10).
• The effects of fat source and proportion in ketogenic diets are significant; certain formulations may mitigate or exacerbate these risks (7 10).
• Existing evidence in humans is more limited, and long-term impacts on glucose regulation, especially in people with or at risk for diabetes, require further study (5 6 7).

Future Research Questions

While the new study advances understanding of the interaction between ketogenic diets and exercise adaptation in the context of high blood sugar, further research is needed to address important gaps. Key areas for future investigation include the translation of animal findings to humans, the long-term safety of ketogenic diets, variability in individual responses, and the interplay between diet composition, metabolic health, and exercise performance.

Research Question	Relevance
Do humans with elevated blood sugar experience similar exercise adaptation benefits from ketogenic diets?	Translating findings from mice to humans is crucial for clinical relevance; existing studies in humans are limited and results are variable (2 3 4 7).
What are the long-term metabolic and cardiovascular effects of ketogenic diets in people with diabetes or prediabetes?	Some animal studies raise concerns about hepatic insulin resistance and lipid accumulation, but long-term impacts in humans remain unclear and under-studied (6 7 10).
How does the source and proportion of dietary fat in ketogenic diets affect glucose metabolism and exercise performance?	Research shows that different fat sources and proportions can lead to divergent outcomes in glucose regulation and metabolic health, but optimal dietary compositions are not defined (6 7 10).
Can less restrictive diets, such as Mediterranean or low-carbohydrate diets, yield similar benefits for exercise adaptation and blood sugar?	Some studies suggest that low-carbohydrate diets may offer metabolic advantages with fewer risks and greater sustainability than strict ketogenic diets, but direct comparisons, particularly regarding exercise adaptation, are limited (7 14).
What individual factors predict the response to ketogenic diets in exercise performance and metabolic health?	Evidence indicates substantial variability in outcomes across individuals, but determinants of this variability (e.g., genetics, baseline health status, gut microbiota) are poorly understood and warrant further study (2 3 5 10).