What Is The Keto Flu & How Can You Prevent It? An RD Explains

Have you tried the ketogenic diet but gave up during the first week due to a headache, anxiety, dizziness, muscle spasms, cravings, or nausea? You may have been experiencing the dreaded “keto flu.” 

While it may be discouraging, the keto flu is not an immediate sign that this diet isn’t for you; it may actually be a sign that your body is still wired for carbohydrates or that it is lacking the conditions necessary for ketone production. You may simply need a more gentle transition. 

So, let’s break down exactly what causes these symptoms and what you can do to ease the transition.

What is the keto flu?

The keto flu is a combination of symptoms that may occur during the transition from using glucose as fuel to using fats and ketones for fuel—which if you didn’t know, is the goal of the low-carb, high-fat keto diet.

Symptoms of the keto flu can include:

  • Headaches
  • Irritability
  • Fatigue
  • Dizziness
  • Muscle spasms
  • Constipation
  • Cravings
  • Nausea

Symptoms are typically more severe when the dietary transition is extreme. So, if you are a total “carb-o-vore,” you are more likely to experience keto flu symptoms than someone who was already eating a lower-carb diet to begin with. Symptoms are also more likely in individuals who have known issues with blood sugar balance.

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What causes the keto flu?

Restricting carbohydrate intake and focusing on healthy fats in your diet comes with many benefits, including weight loss, improved cognitive function, and blood sugar balance, but why the nasty side effects as well? It has to do with electrolyte instability and insulin levels. 

Electrolyte instability

The word carbohydrate has hydrate in it, right? In the body, carbohydrates are broken down and stored as glycogen, and glycogen binds water to it. For every 1 gram of carb stored in the body, there will be about 3 grams of water bound to it. 

When you jump into carbohydrate restriction, it can create a lot of osmotic (water) shifts in the body, throwing off electrolytes and causing muscle cramps, thirst, and headaches. It can also cause bowel irregularity as the colon is a primary area for electrolyte absorption. 

The water loss in the first two to three days can create a nice whoosh on the scale, but it is important to compensate for this loss in water by drinking more fluids to prevent dehydration and electrolyte instability.

Electrolytes, like sodium, potassium, and magnesium, are important for blood pressure balance and play an integral role in neurological, muscular, and metabolic influence in the body. If you are an athlete or you sweat a lot during exercise or use a sauna, be especially mindful to take it easy and consider electrolyte supplementation. Luckily these nutrients are highly available in keto-friendly foods.

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Insulin levels

Beyond the electrolyte and hydration factor, switching from a high or even moderate carb diet to a very low carb diet can cause fluctuations in glucose and insulin levels, which can be at the root of many of the noted flu effects as well.

This is especially true for individuals that have insulin resistance, as their glucose levels may come down more quickly than their insulin levels. Low insulin levels are what signals the liver to make ketones, the alternative form of fuel the body uses in ketosis. But if you aren’t getting that surge of glucose from carbohydrates, and your body doesn’t have conditions appropriate to make ketones, it can make you feel robbed of fuel, triggering keto flu symptoms.

Overall, the metabolic transition from solely using glucose to becoming a fat-burning machine can be a stressor on the body; however, so can exercise, fasting, and many other health-supporting activities. The benefits of ketosis greatly outweigh the symptoms of keto flu, and now that you know why they occur, you can stay ahead of the side effects.

How to avoid the keto flu:

Stay hydrated. 

I recommend half your body weight in fluid ounces of water as a general rule of thumb. But as long as you are getting 2 to 3 liters daily, you are supporting the filtration of your liver and kidneys as well as the lymphatic tissue and optimizing conditions for fat loss. 

Try adding fresh slices of cucumber or sprigs of rosemary to add flavor and support hydration goals. If you are craving sugar, consider slicing one whole strawberry into your water to provide some natural tannic sweetness.

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Get salty.

When you are shifting to a ketogenic diet that is anchored in real foods, be mindful that you are likely eating less sodium, as you are no longer getting it in processed food products. Try to get a minimum of 2 teaspoons of sea salt daily. 

Use salt as a bridge of flavor to bring single-ingredient dishes together, and if you are fasting, consider licking salt or adding to your water to start the day replenishing your electrolyte needs following your a.m. urine flush.

Eat more potassium.

Potassium is not just in bananas! Not that I am scared of bananas per se, but I wouldn’t recommend eating a whole banana during ketosis transition (just one banana packs almost 30 carbs!). Beet greens, salmon, spinach, and avocado are all fantastic sources of potassium to support electrolyte needs without maxing out your carb budget. Stick with whole foods here as an excess of potassium can drive heart palpitations and weakness.

My favorite potassium-filled combo is half an avocado with the juice of 1 lime, cumin, chili powder, and ½ teaspoon of sea salt; eat it with a spoon as a snack, and say goodbye to keto flu!

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Mellow with magnesium.

This essential mineral has more than 300 enzyme functions in our body, and when too low, an individual may experience muscle spasms, anxiety, numbness, and arrhythmia (abnormal heart rate). 

Leafy greens again are a great way to support magnesium levels, and as an added bonus, they are high-volume, high-fiber, and low-calorie. I generally recommend a goal of 2 to 3 cups of leafy greens (measured raw) a day to prevent keto flu. Other great magnesium sources include almonds, pepitas, tuna, and cacao.

Boost ketones with coconut oil.

Your liver is making some serious metabolic shifts when you start the keto diet. It is going from making glucose to ketones, and it may be taxed. Not to mention, if you have insulin resistance as noted, your body may take more time to produce ketones as insulin levels slowly work their way down.

Coconut oil contains medium-chain triglycerides, also known as MCT. MCTs can be converted into ketones in the body, plus they increase satiety, supporting weight loss.

Adding coconut oil to your morning tea or coffee or going right for MCT oil at 1 or 2 tablespoons per day may help get you through the keto flu.

Remember, listen to your body; go slow and steady; breathe; get salty; and channel savory, whole, real foods!


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