"The experiences of symptoms by many people strengthens the evidence for side-effects following the initiation of a ketogenic diet," says Dr. Emmanuelle Bostock of the Menzies Institute for Medical Research of 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."

The effectiveness of the keto diet has only been established for intractable epilepsy, but despite this, 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. To better understand how these symptoms evolve, Bostock and her collaborators 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," explains Bostock. "In the present study, we responsibly and respectfully used public domain online forum posts and analyzed their content to produce new insights into side-effects of the ketogenic diet."

In line with prior medical research, Bostock and her colleagues found reports of headache, difficulty concentrating and gastrointestinal discomfort, following the initiation of a keto diet. Additionally, they 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.

But there is also good news for people experiencing such a "keto flu." The results of this study highlight the sudden onset of symptoms, peaking in the first and dwindling after 4 weeks. Once symptoms manifested, most of them resolved within little more than 2 weeks. Online forum user conversations were generally supportive, sharing remedies to others based on popular beliefs, such as maintaining hydration and correcting electrolyte imbalances.

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. Likewise, experiences of online forum users may not be representative of the larger pool of individuals on keto diet. Nevertheless, the symptom patterns yielded may indicate key lines of questioning for future survey-based approaches.

"Taken together, such reports can bring an illness or side effects into focus and can complement clinical observations and questionnaire-based research," says Bostock. "We see potential for research of this nature to inform all aspects of health care on a continuous basis."