August 22, 2018
The ketogenic diet, which is high in fat and low in carbohydrates, appears to increase the risk of diabetes in the short term, suggests a preliminary study on mice. Researchers found that mice fed the diet began showing signs of insulin resistance, a process that can lead to the development of type 2 diabetes, after only a few days on the diet.
The ketogenic diet — or the “keto” diet for short — has been around for decades. Most popularly, doctors have assigned the keto diet to help control seizures in people with epilepsy, according to the Epilepsy Foundation. But in recent years, people have begun turning to the diet in hopes of losing weight and, in some cases, better managing type 2 diabetes. Studies show that metabolic processes are altered when people consume a diet high in fat, such as meat, and low in carbohydrates, such as bread and pasta. The body shifts into a natural metabolic state called ketosis, during which it burns fat rather than carbs for energy, according to a February 2014 review published in the International Journal of Environmental Research and Public Health. Although carb intake varies depending on which version of keto is at hand, people following the plan typically limit the intake of carbohydrates to less than 5 percent of their daily calories, notes the Chicago Academy of Nutrition and Dietetics.
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The keto diet is intriguing because it appears to run counter to the prevailing wisdom about the importance of lowering fat intake to prevent diabetes and heart disease, says a co-author of the new study, Gerald Grandl, PhD, a postdoctoral researcher at the Institute for Diabetes and Obesity at the Helmholtz Center in Munich. ETH Zurich conducted the study with University Children’s Hospital Zurich.
“The controversy is that, in recent years, the ketogenic diet and low-carb diets have become very popular, both for weight loss and also to treat type 2 diabetes,” Dr. Grandl says. But, he adds, “Traditionally, type 2 diabetes and obesity have been associated with high fat intake.”
A paper published in October 2013 in the British Journal of Nutrition analyzed 13 studies comparing the effects of a ketogenic diet on body weight and heart health to a conventional low-fat diet. The study showed that people on the ketogenic diet achieved greater weight loss.
While studies have demonstrated the weight-loss benefits of the diet, Grandl says, several recent studies that apply more rigorous research techniques to study insulin resistance have suggested detrimental effects. The new study, published in August 2018 in the Journal of Physiology, aimed to better understand the basic biological processes that contribute to the development of type 2 diabetes and the early effects of the ketogenic diet. What people eat impacts the release of glucose, or sugar, in the bloodstream. High glucose levels can, over time, cause insulin resistance. Insulin is the substance released in the body to help manage and regulate sugar in the blood at healthy levels.
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Grandl and his colleagues compared a high-fat diet with a ketogenic diet in mice, feeding the animals specific foods and then conducting tests to understand how their bodies reacted to the diets. The study showed that compared with the mice on the high-fat diet, those on the low-carb, high-fat keto diet appeared healthier while on the keto diet but also began to quickly develop insulin resistance — meaning that their livers were less able to respond to insulin and regulate sugar levels in the blood.
“When we measured fasting plasma levels, we found low insulin and low glucose, which is good — not suggestive of diabetes,” he says. “However, when we challenged the animals with glucose — giving them a relatively large amount of glucose, as they would get by ingesting a meal — we found that their plasma glucose levels went higher than mice on normal chow and stayed high longer.”
This suggests the animals were less able to quickly clear glucose from their blood, he says. “And this is a hallmark of insulin resistance.”
Mice were the focus of this study, which means the effects in humans must still be investigated. But mice are typically considered accurate models of potential biological processes in humans.
The study was also short and does not mean the ketogenic diet causes diabetes, says Julie Stefanski, RD, CDE, a spokesperson for the Academy of Nutrition and Dietetics who was not involved in the research.
“This is a good example of a study where you should not directly apply the information to what you are eating as an individual,” Stefanski says. “The research is interesting, but the study period examined was only three days. While this study showed insulin resistance, it did not in fact show that the mice had diabetes. Making the leap from the results of this study to a headline that concludes a ketogenic diet will cause type 2 diabetes is not supported.”
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More research is needed on the ketogenic diet, Grandl says, but people may have better choices to lose weight and prevent diabetes and heart disease.
“We do not recommend the diet,” he says. “It works for weight loss, and the liver insulin resistance we observe might be transient. But the diet is simply not necessary and probably not the best choice for weight loss,” he says. “Ketogenic diets are often very low in fiber, which may have bad effects on gut health and overall health, especially over a long term. Diets high in fiber and low in fat work equally well or better than low-carb plans, in many studies, to achieve weight loss and lower glucose intolerance.”
Individuals interested in starting a ketogenic diet for weight loss should consult a physician and a registered dietitian, Stefanski says.
“For any individual considering a ketogenic diet, there are laboratory values that a knowledgeable physician should check prior to starting and throughout the course of the diet,” she says. “The best approach is to work with a registered dietitian that is knowledgeable in ketogenic diet therapies and can educate you on ways to make healthier choices on this plan than what dieters would randomly select on their own, along with appropriate supplements that are absolutely necessary on this type of diet.”