MD, PhD, FMedSci, FRSB, FRCP, FRCPEd.

The ketogenic diet (KD) is a currently popular high-fat, low-carbohydrate diet; it limits the intake of glucose which results in the production of ketones by the liver and their uptake as an alternative energy source by the brain. KD is an effective treatment for intractable epilepsy. In addition, it is being promoted as a so-called alternative medicine (SCAM) for a wide range of conditions, including:

  • weight loss,
  • cognitive and memory enhancement,
  • type II diabetes,
  • cancer,
  • neurological and psychiatric disorders.

However, these indications are not supported by good evidence.

A side effect of KD is “keto flu,” a syndrome of transient symptoms generally reported as occurring within the first few weeks of adhering to the diet. These symptoms can feel similar to the flu and are caused by the body adapting to a new diet consisting of very little carbohydrates.

Ketones are by-products of fat breakdown and become the main energy source when following the KD. Normally, fat is reserved as a secondary fuel source to use when glucose is not available. This switch to burning fat for energy is called ketosis. It occurs during specific circumstances, including starvation, fasting … or KD. The KD reduces carbohydrates typically to under 50 grams per day. This drastic reduction may cause withdrawal-like symptoms, similar to those experienced when weaning off an addictive substance.

A recent paper aimed to characterize the pattern of symptoms, severity and time course of keto flu as related by users of online forums. Online forums referring to “keto flu,” “keto-induction,” or “keto-adaptation” in the URL were identified. Passages describing personal experiences of keto flu were categorized with reference to pattern of symptoms, severity, time course, and remedies proposed.

The search criteria identified 75 online forums, 43 met inclusion criteria and contained 448 posts from 300 unique users. Seventy-three made more than one post (mean 3.12, range 2-11). Descriptors of personal experience of keto flu, reported by 101 of 300 users, included 256 symptom descriptions involving 54 discrete symptoms. Commonest symptoms were “flu,” headache, fatigue, nausea, dizziness, “brain fog,” gastrointestinal discomfort, decreased energy, feeling faint and heartbeat alterations.

Symptom reports peaked in the first and dwindled after 4 weeks. Resolution of keto flu symptoms was reported by 8 users between days 3 and 30 (median 4.5 ). Severity of symptoms, reported by 60 users in 40 forums, was categorized as mild (N = 15), moderate (N = 23), or severe (N = 22). Eighteen remedies were proposed by 121 individual users in 225 posts. The following treatments were most frequently recommended (numbers represent the number of times of each recommendation was made):

Increase sodium intake 58
Supplement with electrolytes 38
Drink broth (including bone broth, stock cubes) 27
Increase magnesium 25
Increase potassium 24

I find this paper interesting, not least because of the unusual methodological approach. It seems to confirm that, even though the KD is often recommended as safe, it is associated with significant side-effects. One adverse effect remained unmentioned, while leading to more people discontinuing the diet than any other side-effect: the fact that the diet is quite unpalatable on the long-run and soon puts people off eating. This, of course, might be one mechanism by which KD leads to weight loss.

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