Fasting Ketosis Symptoms: Common Side Effects

Ketosis is one of the natural, physiological effects of the body when fasting. When we’re eating a ketogenic diet or have gone on an extended period of time without food, our bodies will enter ketosis. This is because the body no longer has glucose available and begins breaking down the body’s fatty tissues for energy.

With the ketogenic diet, we’re inducing ketosis by “starving” the body of carbohydrates so that it must turn to fat burning, which has many benefits. Simply fasting by not eating any food can have the same effect. Many people on the ketogenic diet will incorporate fasting to speed up ketosis and also reap the benefits of fasting on keto.

Whether you’re eating a ketogenic diet, simply fasting, or combining the two, your body is entering ketosis. Since the symptoms can be similar, this article covers the common fasting ketosis symptoms, as well as how to deal with them.

Fasting Ketosis Symptoms

It’s important to note that most of these symptoms are temporary as your body is getting adapted to being in ketosis and can be remedied by the tips we cover below.

Ketosis Flu

If you’re using fasting as a way to get into (or get back into) ketosis, you might experience what’s commonly known as the “keto flu” as the body adapts to fat burning. The keto flu typically includes symptoms like:

Common Keto Flu Symptoms

Water Flushing

As your body burns through its glucose and stored glycogen during a fast, a lot of water is released. Your kidneys will also excrete more sodium as insulin drops.  This is why people who start low-carb often experience a big initial loss of water weight and reduced bloating.


With the loss of excess water, the body also flushes out electrolytes like sodium, potassium, and magnesium. This can cause you to feel lightheaded and fatigued more than usual until things balance out more.

Hunger and Sugar Cravings

As your body adjusts to fasting and ketosis, you might experience hunger and/or sugar cravings for a couple days. However, the good news is that eating keto can actually reduce cravings for unhealthy foods, especially sugars and carbs. Once you get your body running on ketones, fasting feels much easier.

Keto Breath

The early stages of ketosis can include an interesting smell on the breath. This is from the release of the ketone acetone, which is released through the breath. However, this wears off within the first week or so.

Digestive Concerns

Some people may notice a change in bowel movement during the first phases of ketosis. Diarrhea or constipation may occur as changes happen in your gut’s microbiome. Other reasons could include not staying hydrated enough or sensitivity to certain keto foods.

Taking psyllium husk or activated charcoal during this phase can help those dealing with diarrhea.

Muscle Cramps

Mineral imbalance or lack of hydration can cause muscle cramps in some people when in ketosis. This is temporary, and replenishing both can remedy this.

Initially Less Energy

“Cleaner,” more steady energy is a perk of both a ketogenic diet and intermittent fasting, but in the beginning stages of ketosis, one might experience a drop in energy and strength as the body adapts to using ketones for fuel.

Heart Palpitations

An increase in heart rate may happen within the first few weeks of fasting or being in ketosis. If you normally have lower blood pressure, this is more likely for you. Heart palpitations can occur simply from lack of enough water and salt, making it all the more important to stay hydrated and include salt when you eat!

Since a ketogenic diet can help improve blood pressure, those on medications that affect blood pressure may need to speak with their doctor about dosage.

Now that we’ve covered some of the main concerns when fasting and entering ketosis, let’s discuss how to best deal with them as your body adjusts.

How to Deal with Fasting Ketosis Symptoms

While most fasting symptoms of switching to ketosis only last a few days to a couple weeks, there are things we can do to reduce the symptoms and make the process more pleasant:

How to Deal with Fasting Ketosis Symptoms

Stay very hydrated: You can expect a big flush in water weight, which can leave you dehydrated and exacerbate the above symptoms. Be sure to drink plenty of water and consume bone broths that are rich in minerals.

Increase your intake of salt: As the body flushes out water from lack of carbs, sodium is excreted as well, so replacing that salt is important. For best results, use high-quality sea salt, such as Celtic sea salt or Himalayan sea salt, each time you eat.

Eat mineral-rich foods: If you’re doing intermittent fasting, be sure to eat high-nutrient meals during your eating windows to replace any lost electrolytes. Eat plenty of leafy greens, celery, seaweed, cucumber, meat, poultry, and fish, avocados, and high-fat dairy foods (if dairy agrees with you).

Supplement with magnesium: Taking magnesium citrate can help with balancing hydration and electrolyte levels. Be careful with this if you experience diarrhea, however. And if you have kidney problems, check with your doctor before taking magnesium supplements.

Take exogenous ketones: One way to avoid keto flu symptoms is by taking exogenous ketones. They provide your body with extra ketones to use for fuel during the transition, getting you into ketosis faster. Plus, getting into ketosis faster can help reduce all of the common symptoms mentioned above.

General self-care: Overall, just make sure you’re taking care of yourself. Whether you’re starting a new ketogenic diet, trying intermittent fasting, or both, the change can be an adjustment at first. Know you’re doing something good for yourself, and keep your health in mind through the whole process.

Positive Fasting Ketosis Symptoms

If these symptoms have you feeling nervous, here’s a reminder of the POSITIVE symptoms of fasting in ketosis:

Weight loss and appetite suppression: Not only does fasting in ketosis naturally reduce food intake and burn fat, eating a high-fat, low-carb diet also increases satiety and naturally reduces appetite.

Boosted energy: After you get through the initial phases of ketosis, a great benefit of switching from a carb-heavy diet to a low-carb diet is a more steady stream of energy. And fasting in ketosis reduces spikes in blood sugar even more, leaving you with more stable energy levels throughout the day.

Higher mental clarity and cognition: The ketones produced when burning fat, whether you’re fasting or eating a ketogenic diet, are able to cross the blood-brain barrier, providing energy for the brain and even providing neuroprotective benefits.

Long-term health benefits: Besides the more immediate positive symptoms of fasting in ketosis, there are some amazing long-term benefits of running on fat instead of glucose, including decreasing the risk of diseases like diabetes, Alzheimer’s, and even cancer.

Take Home Message

Eating a ketogenic diet and fasting regularly are both amazing ways to take care of your health and increase your chances of a long, healthy life. Being aware of the symptoms can help you avoid any initially uncomfortable side effects and get the most out of this lifestyle.

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What to read next:

Is Coconut Flour Keto Friendly

Responses (10)

    1. Hi Kim! Try putting Cacao butter/nibs in your coffee or tea. It taste just like chocolate…because it is the base for candy bars. Make chocolate fat bombs. I eat a little one after dinner or when I’m doing intermittent fasting. I put sea salt in my recipe for the potassium and magnesium we need to stay alert.

  1. I’ve been using your Chocolate Sea Salt Exogenous Keytones during my 3 day fast (blended in decaf coffee) and I can’t help but feel that it’s “cheating”. Is this breaking my fast? I typically stick to straight water during fasts.

  2. Anyone experiencing facial flushing? Back on the Keto wagon and here it is again. Haven’t noticed if for the last few months of being off Keto.

    1. Yes, I experience that as well. Since I started my Keto lifestyle I’ve been experiencing facial flushing especially on my cheeks and nose and a general feeling of my skin being warmer. I also sweat a lot more than usual. I can’t find much info on this online but have read about others experiencing the same.
      I would like to know what causes it though – perhaps increased metabolism…?

      1. Are you taking a multivitamin that has a lot of niacin or a B vitamin complex? Sounds like niacin flush to me. Cut back on your supplementing and get your nutrition from vegetables and meat, maybe the occasional piece of fruit. Just because fruit has carbs doesn’t make it evil. Nature is really good at allocations.

      2. You are sweating because on Keto lifestyle, you are always loosing water because you are losing carbs and carbs in the body as glycogen in muscles are attached to water molecules. Also it depends on how many of grams of carbs you are taking. You need to eat greens, veggies and fruit. These are very important especially if you are continously doing less in low tens of carbs.

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