‘Keto Flu’: Symptoms Presenting During the Beginning of a Ketogenic Diet

The ketogenic diet (KD), which has gained a recent surge in popularity, focuses on consuming higher levels of fat and lower levels of carbohydrates. This causes the liver to produce ketones, which the brain uses as an alternate energy source, and lowers glucose levels. Studies support the use of KD to treat intractable epilepsy; data are limited on its effects on weight loss, cognitive and memory enhancement, type 2 diabetes, cancer, and neurological and psychiatric disorders.

KD followers often address “keto flu,” characterized by flu-like symptoms people sometimes experience when first starting the diet. A study evaluated the keto flu’s pattern of symptoms, severity, and time course as described by people posting in online forums.

The researchers used Google to locate online forums discussing “keto flu,” “keto-induction,” or “keto-adaptation.” They assessed users’ personal accounts of keto flu and manually categorized posts in terms of symptom pattern, severity, time course, and remedies proposed.

Of 75 online platforms identified, 43 were included in the study, encompassing 448 posts from 300 unique users; 73 users made multiple posts (mean, 3.12 posts). About one-third of users (n=101) shared personal accounts of keto flu, providing 256 symptom descriptions encompassing 54 discrete symptoms. The most commonly reported symptoms were “flu,” headache, fatigue, nausea, dizziness, “brain fog,” gastrointestinal discomfort, decreased energy, feeling faint, and heartbeat alterations. After peaking during week one, symptoms decreased after four weeks; symptoms resolved between days three and 30 (median, 4.5 days), according to reports from eight people. Discussions of symptom severity were identified in 40 forums, with 60 users posting; 15 categorized their symptoms as mild, 23 as moderate, and 22 as severe. A total of 18 remedies were shared by 121 users in 225 posts.

“Reports of personal experiences of keto flu by many individuals suggest that the physiological and perhaps psychological changes associated with KD result in the manifestation of an induction and adaptation related syndrome. It is not clear whether this is to be understood in the form of an illness state produced by nutritional and perhaps immune imbalance or is indicative of an adaptive bodily process triggered by KD,” the authors concluded. “As the repository of online posts increases, it will likely be possible to discern an increasingly informative picture of the effects of KD and the features and mechanisms of keto flu.”