Be Alert! Ketogenic Diets May Cause Temporary Flu-like Symptoms!

According to a new study, the first weeks of a ketogenic diet may have a lot of flu-like symptoms, including nausea, fatigue and dizziness.

The study was recently published in the journal Frontiers in Nutrition. The researchers extracted data from the experiences of 101 people who started on a ketogenic diet and described their symptoms in 43 forums. As with anecdotal reports of ketogenic influenza—the symptoms of influenza that began with such a high-fat, medium-protein, low-carbohydrate diet gradually worsened in the first seven days of starting a new ketogenic diet, but gradually decreased over time and eventually disappeared spontaneously after about 4 weeks.

Dr. Emmanuelle Bostock, one of the authors of the study and a researcher at the Menzies Institute for Medical Research at the University of Tasmania in Australia, said: "We sought to describe the nature of ketogenic influenza because the incidence in media reports is inconsistent with that in the academic literature. We found that some users of online forums self-reported flu-like symptoms, which usually occurred in the first few weeks of starting a diet."

In the 1920s, ketogenic foods first emerged as drugs for the treatment of epilepsy. But recently, the ketogenic diet has become a health boom because it is thought to lose weight by forcing the body into a state called ketogenesis. When the human body is in this state, cells take energy from compounds called ketones, which are extracted from fatty acids. Experts are still unsure why it leads to weight loss, and studies have generally failed to demonstrate that a ketogenic diet is more effective than other weight loss strategies. The ketogenic diet seems to have an unexpected difference from other diets, that is, it predisposes to flu-like symptoms, at least in the first few weeks of starting this diet.

"I did see some clients getting ketogenic flu," said nutritionist Ginger Hultin, a spokesman for the Nutrition and Dietetics Society. Hultin was not involved in the study. "Some people have few symptoms, some have these symptoms, and some have more severe symptoms."

To quantify the phenomenon, Bostock and her colleagues identified consistent complaints from 43 online forums. The researchers found that within the first few weeks of starting the ketogenic diet, people reported sudden onset of headache, stomach pain, nausea, and other flu-like symptoms.

The researchers say it is not clear why a ketogenic diet produces this effect, but they suspect that this may be related to changes in bacteria and other microbes in the gut when people start consuming a ketogenic diet.

For example, the ketogenic diet excludes many foods that support gut bacteria, such as starchy vegetables and whole grains. Given that many studies have found a link between the brain and the gut, changes in gut bacteria may contribute to some of the symptoms of ketogenic influenza.

More importantly, many people start eating ketones in order to reduce carbohydrate intake, which requires major changes in the food they eat. Carbohydrate intake can cause symptoms similar to caffeine withdrawal.

However, an important limitation of this new study is that the data are entirely derived from online conversations, and there is no evidence that people who describe symptoms are consuming a ketogenic diet, let alone experiencing ketosis. "More clinical studies need to be done because this is only a review of online forums," Hultin said. But Bostock hopes that this pilot study will lay the groundwork for future exploration of the side effects of the ketogenic diet in carefully designed clinical trials.