Keto Flu: What It Is and How to Get Rid of It

One downside of keto? Some people experience what’s called the “keto flu,” a temporary illness-like state that sets in soon after starting the diet. The symptoms of the keto flu can make people feel so bad that they give up following the diet altogether. But with some know-how and tips from experts, you can help prevent and manage the keto flu. Here’s how.

Not a true medical diagnosis, “the keto flu describes a short-term, difficult period that occurs as your body is in the early period of transitioning to the keto diet,” says Lindsay Malone, RDN, an integrative and functional medicine dietitian and an instructor in the department of nutrition at the school of medicine at Case Western Reserve University in Cleveland. There are several potential reasons you may feel sick and run-down after starting on keto, which we’ll explore below.

Keto flu symptoms are wide-ranging, but they really can mimic the flu in some ways. Here are some of the symptoms you may experience, according to Temple Stewart, RD, a registered dietitian in Phoenix, Arizona, who specializes in the keto diet:

• Brain fog
• Difficulty sleeping
• Fatigue
• Headache
• Irritability
• Muscle cramps
• Nausea

How Keto Flu Differs From Other Illnesses

The keto flu is the result of your body transition to the keto diet. It is not the same as having the flu because of an infection with the influenza virus or one of the many viruses that causes the common cold. Both the keto flu and regular flu or illness can have similar symptoms, but you might suspect your symptoms are the result of the “keto flu” if you’ve recently started on the diet. It’s also possible to get sick with the flu coincidentally as you start on a new diet.

• Cough
• Fatigue
• Fever
• Headaches
• Muscle or body aches
• Runny, stuffy nose
• Sore throat

Not everyone gets the keto flu when they start the keto diet, says Stewart. But understanding its causes can help you manage your symptoms so you can feel better fast — or prevent it entirely.

Experts say that there are several potential reasons why you may have the keto flu.

A Fast ‘Withdrawal’ of Simple Carbohydrates

“When we take away simple carbs from the diet, our body is still looking for but not able to access that quick source of energy,” says Malone. This can also affect your blood sugar, which impacts your energy, adds Stewart. If your body has become accustomed to running on higher blood sugar levels, you may really feel these effects.

Changes in Electrolyte Levels Like Sodium and Potassium

Malone says that as you transition to eating a higher-fat diet, the foods you will eat change, and that can affect nutrient intake. While this is different for everyone, you may remove most processed foods (that are typically high in sodium), as well as some fruits and vegetables (which contain potassium) when you go on the keto diet.

Dehydration

“When you drastically reduce carbohydrates in your diet, you’ll deplete your glycogen stores, which hold a lot of water,” explains Stewart. This leads to dehydration and can also affect your electrolyte levels, she says. Stewart says that in some ways, the keto flu is akin to a case of mild dehydration.

Good news: The keto flu typically lasts for about two or three days, says Malone. For some people, the effects can last longer, but after about a week of starting the keto diet, you will likely begin feeling like yourself again, says Stewart. That’s because after days No. 4–7 of starting keto, the body typically becomes more efficient at producing ketones, she says.

Employing the remedies below can help make this transition time easier for your body. Or, if you have yet to start the keto diet, you’re in luck: “My whole goal is to help clients avoid the keto flu altogether because that’s when people throw in the towel,” Stewart says.

The keto flu isn’t inevitable, and you’ll be able to tolerate the first week of the diet better if you follow these tips.

Reduce Your Carbohydrate Intake Slowly

This is the approach Stewart uses with her clients. She encourages tapering your carb sources, which will be less of a shock to your system. First, cut out foods that have a tendency to spike your blood sugar, like simple carbs (cakes, candy, and sugar-sweetened beverages). Then, you can begin to reduce the portion sizes of other high-carb foods, like grains and starchy vegetables.

Take in Additional Electrolytes

Try a no-sugar-added electrolyte powder that you can add to your water, suggests Malone. Bone broth, which is an electrolyte-packed drink, and more potassium-rich foods like avocados and leafy greens, are also recommended, adds Stewart.

Consider MCT Oil

“Medium-chain triglyceride (MCT) fats can be useful because they enter the bloodstream directly as a fuel source,” says Malone. “They can be a good way to get a bit of an energy boost while the body is still ramping up ketone production,” she explains. MCTs, often available as an oil or powder, can be mixed into shakes and smoothies, incorporated into salad dressings, added to your coffee, and more.

Stay Hydrated

Don’t underestimate your body’s need for water. “If we can get ahead of dehydration in the early days of starting the diet, you can avoid a lot of these symptoms,” says Stewart. She recommends keeping your water bottle handy throughout the day.

Listen to Your Body

Finally, if you’re fighting fatigue, make sure that you’re resting in the early days of the diet, says Stewart. Don’t put pressure on yourself to maintain an intense exercise routine or push through your normal day-to-day. Give yourself some time to get through this period, and you’ll start to feel like yourself again in no time.

If you have symptoms that indicate an upper respiratory infection (fever and chills, sore throat, runny nose, sneezing), it may not be the keto flu at all. Similarly, if the fatigue, brain fog, and headaches linger longer than a week of starting the keto diet, something else may be contributing to your symptoms, says Stewart.

At this point, consider connecting with your provider to investigate other causes (like a viral illness). If it’s diet-related and you are unsure if you are approaching the keto diet correctly or if it’s the right option for you, connect with a registered dietitian.

The keto flu is a potential side effect of starting the keto diet. Although it doesn’t happen to everyone, symptoms include headaches, muscle cramping, and fatigue. Symptoms may last for two or three days, but they should be gone after week one of the diet. Reduce your carb intake gradually, stay hydrated, and take extra electrolytes, and you may avoid the keto flu altogether.