What is keto flu?

By | October 18, 2018

Many people have decided to try the ketogenic diet for weight loss. The most recent evidence shows that reducing your carbohydrate intake to a minimum may help you shed a few pounds, at least in the first few weeks to months. However, we don’t really know whether, over the long term, achieving and maintaining ketosis is better for weight loss than other diets. Almost any intervention can cause undesirable consequences, and the ketogenic diet is no different. One of the most well-publicized complications of ketosis is something called “keto flu.”

What is keto flu?

The so-called keto flu is a group of symptoms that may appear two to seven days after starting a ketogenic diet. Headache, foggy brain, fatigue, irritability, nausea, difficulty sleeping, and constipation are just some of the symptoms of this condition, which is not recognized by medicine. A search for this term yields not a single result on PubMed, the library of indexed medical research journals. On the other hand, an internet search will yield thousands of blogs and articles about keto flu.

It is tricky to describe exactly what happens after the diet change, because we are left with only our own observations and experiences. These symptoms may not even be unique to the ketogenic diet; some of my patients describe similar symptoms after they cut back on processed foods, or decide to follow an elimination or an anti-inflammatory diet.

What causes keto flu?

Well, we don’t really know why some people feel so bad after this dietary change. Is it related to a detox factor? Is it due to a carb withdrawal? Is there an immunologic reaction? Or is this a result of a change in the gut microbiome? Whatever the reason is, it appears the symptoms attributed to the keto flu may happen, not to everyone but to some people, after “cleaning up” their diet.

What to do for keto flu?

If you decide for whatever reason to change your diet and feel tired and a little off, do not become exasperated and lose hope. Here are a few tips:

  • There is no need to go online and buy any expensive supplements. Many websites are trying to make big bucks selling products to make you feel better without any data to back up those claims.
  • Despite its name, this is not like the flu. You will not develop a fever and the symptoms can hardly ever make you incapacitated. If you feel very ill, consider visiting your doctor, as something else may be happening.
  • Make sure you drink plenty of water. Some diets can make you dehydrated.
  • Eat more often and make sure you have plenty of colorful vegetables. Switching from a standard American diet, rich in simple carbs, trans fats, and saturated fat, is a big change in how your cells use energy. Food is not only calories and energy, it is communication to your cells.
  • Do not give up if you are committed to a plan. You may feel exhausted for a few days, but at the end of a week, your energy level will most likely return to normal and you may feel even better.
  • If everything else fails, consider easing into the new diet more slowly, instead of “cold turkey.”

Undesirable symptoms may show up in the first few days after changing what you eat. But this should not be the deciding factor when choosing what to put on your plate. Ideally, you should have the most comprehensive and nutritionally dense diet possible, and the Mediterranean and DASH diets have the best evidence to support living a long and healthy life.


Harvard Health Blog