What Is the Keto Flu, and How Do You Treat It?

If you’re looking into starting the ketogenic diet, it doesn’t take much research before you encounter the dreaded “keto flu.” Symptoms, such as fatigue, headaches and nausea, can be enough to knock even the most dedicated dieter off the wagon. But before you give this low-carb, high-fat diet a no-go, we’ve got some important info about the keto flu, and a few tips for avoiding it.

The Science Behind Ketosis

The ketogenic diet focuses on limiting carbohydrates and increasing fat intake in your diet. With this way of eating, your body operates from the fat you consume, and as a result, you also easily burn fat.

According to Dr. Adam Nally, a board-certified obesity medicine physician, ketogenic expert and author of The Keto Cure, the ketogenic diet also helps reduce insulin overproduction — a common symptom of the American diet. Insulin overproduction can increase the likelihood of developing other chronic diseases, like diabetes and metabolic syndrome.

What Causes the Keto Flu?

 Dr. Nally says that the body’s levels of insulin and salt are related. “What happens when you switch into ketosis, [is that] your insulin level has reduced, and the need to retain salt has been reduced,” he explains. Therefore, your body rapidly expels excess salt. If your body loses too much salt (and other electrolytes, such as potassium), you can start to feel flu-like symptoms including fatigue, headaches, brain fog, dizziness, nausea, irritability, lightheadedness and leg cramps.

Another potential cause of fatigue, says Dr. Nally, is not consuming enough fat when on a ketogenic diet. “Because we’ve created a fat phobia, some people just aren’t adding back enough fat.” Protein is generally used by the body to maintain muscles, skin, hair and nails, says Dr. Nally, whereas carbs are usually used for energy. When you remove carbs in a ketogenic diet, it’s essential that you consume enough fat to provide energy through ketogenesis.

How to Prevent and Alleviate the Keto Flu

The keto flu tends to strike around three to five days into a keto diet and usually goes away on its own, says Dr. Nally. “The body will attempt to compensate [for lost salt] and in many cases it does,” he says. But if you’re not consuming enough salt and potassium, it can prolong keto flu symptoms. If simply salting your food a little more doesn’t provide relief, try increasing electrolyte intake through sports drinks. “Often by just adding some bone broth or bouillon broth, symptoms will improve in minutes,” says Dr. Nally.

Of course, you’ll also want to make sure you’re consuming enough calories overall and that your calorie intake includes enough fat. High-fat snacks, known as “fat bombs” in the keto community, can be one way to keep fat intake up. It may also be worth investing in a keto meal plan or keto-specific recipes to help keep track of your macronutrient intake.

When You Should See a Doctor

For the most part, those who experience keto flu symptoms won’t want to exercise, but Dr. Nally says there’s no reason not to work out if you feel like it. Simply stay hydrated and keep your electrolytes up.

But if your headaches don’t get better, and you continue to vomit or feel weakness and fatigue, it’s time to see your MD. People with diabetes who use the ketogenic diet to moderate blood sugar may want to test their ketone levels, in addition to blood sugar, to make sure they aren’t at risk for developing diabetic ketoacidosis. Even those without other pre-existing conditions keep eye out for potential adverse reactions.

As long as symptoms resolve relatively quickly and painlessly, though — as they should — there’s no reason the keto flu should keep you from trying out this diet program.