Keto Flu

You’ve just started the diet and are looking forward to a boost in energy, but instead you feel light headed, irritable, and have trouble focusing.

Not to worry: you’re experiencing what is called “keto flu.” It’s not an actual flu — think of it more like sugar withdrawals. As you transition from the standard American diet, full of sugars and carbs, your body also needs to switch over from using glucose for energy to using ketones. Keto flu is often short-lived and means you are well on the way to priming your fat-burning engine.

Symptoms usually start on day two and can last for up to a week, but usually don’t last past two or three days. They may only be mild — or not happen at all. Symptoms include:

  • Fatigue

  • Headache

  • Irritability

  • Brain fog, difficulty focusing

  • Lightheadedness, dizziness

  • Weakness

  • Sugar cravings

  • Nausea

What Causes Keto Flu?

Often, the keto process begins with a loss of water weight as well as the salt that leaves the body with it. This loss is quick and could be anywhere between a few pounds to ten pounds, depending on your starting weight. People who regularly eat over 100g of carbs a day (as most Americans do) end up storing some of the sugars from these carbs as glycogen in their muscles and liver — a form of quick-access energy. Each gram of glycogen is bound to three to four grams of water, adding up to a lot of water weight. As fewer and fewer carbs are consumed, the body quickly burns through this stored glycogen — and all that water gets flushed out, taking a good bit of salt along with it.

Sticking It out Through the Flu

Since keto flu symptoms are part of the transition process, they typically disappear shortly after your body adapts. If they are unmanageable, though, here are some quick solutions:

Drink water with salt. Keto flu is most commonly caused by dehydration from the substantial loss of water weight and the salt present in the water. Add half a teaspoon of salt to a large (12–16 oz.) glass of water and drink slowly. This can reduce symptoms in 15–30 minutes. For a tastier option, try 12 oz. of broth. Chicken, beef, bone, or bouillon will do. Be sure not to choose the reduced salt version. Repeat at least twice daily as needed for the first week and then continue if symptoms have not subsided.  

Eat more fat. If salt isn’t helping, make sure you are eating enough fat — eating to your fat macro can speed up the adaptation process. See Adding Fat and Flavor to Your Meals for tips and tricks on adding more to your diet.

Eat a few more carbs. If you are still experiencing symptoms after trying salt and fat, try eating a few carbs from fruit. Consuming more carbs will lead to a slower transition into weight loss and health improvements, but can make the symptoms much more manageable. Eat a ¼ cup of blueberries, blackberries, strawberries, or raspberries twice a day.