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- The keto flu occurs in the first days of going keto as your body adjusts to burning fat for energy.
- Symptoms of the keto flu include fatigue, irritability, nausea, constipation, and dizziness.
- To avoid or treat the keto flu, stay hydrated, eat more electrolytes, and avoid intense exercise.
- Visit Insider's Health Reference library for more advice.
The keto diet has won wide acclaim for its ability to help people lose weight quickly or manage diabetes. However, these benefits can come with a price – the keto flu.
The keto flu is when you experience flu-like symptoms as your body transitions to the new diet.
Here is what you need to know about the keto flu from common symptoms, how long it will last, and prevention tips.
What is the keto flu?
The keto flu is your body's reaction to the keto diet's extremely low-carb eating plan, says Lori Shemek, PhD, a nutrition and weight loss expert with a virtual private practice.
Normally, your body pulls energy from three main sources: carbs, proteins, and fat. "We're using all of them to some degree all of the time but when we run out of one energy source our body will prioritize another," says Scott Keatley, a registered dietitian-nutritionist at Keatley MNT.
That's exactly what's happening if you're doing the keto diet correctly. Your body goes from primarily burning carbs for energy to burning fat instead. In fact, that's where the keto diet gets its name. Your body converts fat from your food into a form of energy your body can use called ketones.
"Changing your energy source from carbohydrates to fat means that your body has to break things down differently and this takes more time, which is why so many people feel like their energy levels are depleted during this transition," says Keatley.
Keto flu symptoms
The duration and severity of keto-flu symptoms vary from person to person, and some people may not experience any symptoms at all.
"Depending on your genetics you may never experience [keto flu]," says Shemek. Some people are more "metabolically flexible" than others, meaning they have an easier time transitioning between energy sources.
For example, a small 2020 study found one-third of people experienced keto flu symptoms ranging from mild to severe. That means two-thirds experienced no symptoms at all.
See a doctor if you are still feeling under the weather after a week or two of starting the diet.
5 tips to avoid and treat keto flu
The good news is that there are measures you can take before and during keto to avoid and treat keto flu symptoms.
1. Stay hydrated
Going keto puts you at an increased risk of dehydration. That's because you may need to go to the bathroom more as your body burns ketones instead of carbs.
Even being mildly dehydrated will cause or exacerbate keto flu symptoms like fatigue and dizziness, says Shemek. Therefore, it's important to drink plenty of water throughout to replenish lost fluids.
2. Choose high-fiber foods
Eating keto-friendly foods rich in fiber can help keep digestive issues like constipation at bay.
Fiber promotes a healthy gut by providing bulk and water to your stools, making them easier to pass. Adults should aim to consume at least 25-30 grams of fiber per day.
This can be difficult to achieve while going keto as high-fiber foods like whole grains, fruits, and starchy vegetables are limited. While you only have 50 grams of carbohydrates a day on keto, it's important to make sure these carbs count, says Keatley.
Keatley suggests eating fibrous vegetables like:
- Artichokes
- Brussels sprouts
- Broccoli
3. Replace electrolytes
Not only are you using the bathroom more on keto, but you're going to excrete sodium and potassium through your urine, which are two electrolytes essential for staying hydrated.
Therefore, it's important to consume adequate amounts of electrolyte-rich foods like:
- Broccoli
- Swiss chard
- Avocados
- White meat and poultry
4. Go easy on the exercise
Depending on the type of exercise you are doing, the activity can exacerbate keto-flu symptoms like fatigue and digestive issues. That's because our bodies are used to pulling energy from carbohydrates during an intense activity like HITT workouts or running, says Keatley.
While you're transitioning to ketosis, opt for low to moderate activities like walking or leisurely biking as your body adjusts to a new fuel source.
5. Ease into the diet
Slowly cutting carbs before jumping into the keto diet can help your body more e
easily transition to using fat as its main fuel source. This may help you avoid uncomfortable symptoms associated with the keto-flu, like digestive issues.
Consider starting with a less intense moderate- to low-carb diet or making small keto-friendly swaps to your normal meals.
Insider's takeaway
The keto-flu is a natural response to switching your primary energy source from carbs to fats. Not everyone will experience keto-flu symptoms, but those that do usually experience them in the first few days of starting the diet and begin to feel better within a week.
The keto diet is not for everyone and can cause health issues, like nutrient deficiencies, if it's not done properly. For this reason, consider consulting a registered dietitian or health professional before going keto.