A ketogenic diet may cause several flu-like symptoms within the first few weeks on the diet with very low-carbohydrate and high-fat content, according to a new study.
The study, published in the journal Frontiers in Nutrition, found that these symptoms peak in the first seven days and dwindle after four weeks and range in severity, as reported by users on social media.
These reports reveal common but yet unknown symptoms, such as flu fatigue, nausea, dizziness, decreased energy, feeling faint and heartbeat alterations, the researchers said.
"The experiences of symptoms by many people strengthens the evidence for side-effects following the initiation of a ketogenic diet," said Emmanuelle Bostock from the University of Tasmania in Australia.
"These consumers have the most immediate experience of effects and side-effects and many choose to report and share these in online forums," Bostock said.
The effectiveness of the keto diet has only been established for intractable epilepsy, the researchers said
Despite this, they said, a ketogenic diet is often self-administered for weight loss, cognitive and memory enhancement, type 2 diabetes or cancer.
A commonly discussed side effect of this diet is the so-called "keto flu", a cluster of transient symptoms that occur within the first few weeks on the diet, according to the researchers.
To better understand how these symptoms evolve, they identified 43 online forums referring to "keto flu" and manually gathered personal experiences of 101 people describing symptoms, severity and time course.
"We focused on social media because of its widespread use for discussion of health topics, which makes it practical to harness the experience of people who have tried the treatment in question," said Bostock.
"In the present study, we responsibly and respectfully used public domain online forum posts and analysed their content to produce new insights into side-effects of the ketogenic diet," Bostock said.
The researchers found reports of headache, difficulty concentrating and gastrointestinal discomfort, following the initiation of a keto diet.
They also reveal further common symptoms, such as flu, fatigue, nausea, dizziness, decreased energy, feeling faint and heartbeat alterations.
Consumers often experienced more than one symptom, with differing degrees of severity, the researchers said.
However, there is also good news for people experiencing such a "keto flu".
The results of this study were limited to conversation threads in online forums and therefore lack of any confirmatory evidence that ketone levels were raised, according to the researchers.
Experiences of online forum users may not be representative of the larger pool of individuals on keto diet, they said.