7 Keto Side Effects: Is Ketosis Safe?

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Ketosis | Keto Side Effects | How to Avoid | Summary | FAQ | Studies

Keto is a low-carbohydrate, high-fat (LCHF) diet that is particularly effective at losing weight while improving blood lipids (Yancy et al. 20041).

Ketogenic diets were developed 100 years ago to treat epilepsy and are still in successful clinal use today (Neal et al. 20082).

The Internet is full of a wide variety of information about the metabolic state of ketosis. Based on recent studies, you will learn about the possible side effects of keto in this article.

Is Ketosis Bad for You?

Ketosis is a natural metabolic process.

There are two ways to induce ketosis:

Because it mobilizes stored body fat when food is unavailable for extended periods, ketosis has ensured the survival of humankind.

The fat-storage hormone insulin blocks the breakdown of body fat (Meijssen et al. 20013).

However, in the absence of carbohydrates, insulin levels drop sharply. So the body can use stored fat for energy production.

The broken-down fat enters the liver, which converts some into ketones.

In ketosis, ketones predominantly replace carbohydrates and provide energy to the brain, heart, and muscles (Evans et al. 20174).

With a few exceptions in the brain, kidneys, and eyes, all cells can be 100% sourced by fat energy. However, the liver makes the necessary amount of glucose from byproducts of fat breakdown (Melkonian et al. 20205).

Hence, Ketosis is fundamentally not dangerous. Studies confirm that a keto diet does not lead to significant side effects, even over a long period (Dashti et al. 20046).

The common fear of ketosis originates in the confusion about diabetic ketoacidosis (DKA). This serious complication can occur in people with type 1 diabetes if they do not regulate their blood glucose levels.

The natural metabolic state of ketosis, on the other hand, can help against type 2 diabetes, metabolic syndrome, insulin resistance, cancer, epilepsy, Alzheimer’s, Parkinson’s, and other chronic conditions (Volek et al. 20057Weber et al. 20188Neal et al. 20089Choi et al. 202110).

However, it may take time for the body to become fat-adapted.

Depending on the previous lifestyle, it takes 3-6 weeks for the body to relearn to consume fat as a primary energy source.

Side effects may occur during this transition period.

Common Keto Diet Side Effects

When your body first switches to ketosis, side effects can occur. However, most observations are not permanent. Some side effects also turn out to be long-term benefits.

1. Fewer Cravings

Ketogenic diets curb appetite in several ways at once.

While the consumption of fats inhibits the release of hunger hormones, it increases satiety hormones (Beck 200611Dockray et al. 201212).

Some satiety hormones even increase in proportion to the number of fatty acids consumed in the diet (Pironi et al. 199313).

However, not only healthy fats but also ketosis itself works against cravings. High ketone levels reduce the hunger hormone ghrelin (Gibson et al. 201514).

Curbed hunger is an often overlooked reason why people on keto can be successful in the long run.

Eating less is a welcome side effect of keto

2. Weight Loss

The keto diet usually produces a quick weight loss of two to three kilograms in the first week.

The reason for this is water retention, which is broken down. Low insulin levels allow the body to empty its carbohydrate stores.

Carbohydrates are stored as glycogen, mainly in the liver and partly in the muscles. Glycogen consists of one part carbohydrate and three parts water.

Therefore, by depleting the carbohydrate stores, you lose water weight quickly. The initial weight loss is, therefore, not body fat.

But don’t worry: once the glycogen stores are empty, the body is forced to use fat for energy.

Overweight people can lose significantly more weight with keto than low-fat diets or calorie restrictions.

Researchers also welcome the side effects of keto weight loss: Improved insulin sensitivity and blood lipid levels (Samaha et al. 200315).

Furthermore, ketosis consumes more calories than conventional diets (Ebbeling et al. 201216).

People on ketogenic diets also eat less subconsciously (McClernon et al. 200717).

3. Frequent Urination

As we just heard, keto depletes water deposits in the body. As a result, you have to go to the toilet more often, especially in the first weeks.

It is not a big deal as long as you drink plenty of water.

When the glycogen stores are empty and you are fat-adapted, you will have to urinate less.

4. Muscle Cramps

The ketogenic diet keeps blood sugar and insulin levels stable and low.

Few people know that insulin binds salt in your body. For most people, sugar is to blame for the kidneys not excreting enough salt.

Keto does the opposite. The kidneys actively excrete salt. As a result, magnesium and other electrolytes leave the body with sodium (Tiwari et al. 200718).

When you lack sodium and magnesium, you get muscle cramps more easily. Therefore, providing electrolytes to the body is crucial, especially if you are starting keto.

I recommend drinking natural mineral water as it contains sodium, magnesium, and calcium, which you will flush out initially.

Don’t skimp on salt when you’re on a ketogenic diet. Unlike sugar, salt has a negative feedback loop. That means when your body has had enough, you won’t feel like it, either. No one likes salty soup.

If you like salt on keto, it’s not only okay. It’s healthy. In addition, salt is the natural antagonist of sugar and helps you lose weight (Sakuyama et al. 201619).

5. Keto Flu

The increased excretion of salt leads to another phenomenon, probably the most well-known side effect of ketogenic diets: keto flu.

Symptoms of keto flu are physical and predominantly caused by sodium deficiency. The five most common complaints are (Bostock et al. 202020):

  • Flu symptoms
  • Headache
  • Fatigue
  • Nausea
  • Dizziness

The keto flu usually does not last long. Once the body has learned to burn fat for energy again, the symptoms disappear.

Keto flu may not occur or last several days, depending on your previous lifestyle.

However, most people can quickly relieve keto flu symptoms with adequate salt and water intake.

Flu symptoms are a common side effect of ketosis

6. Keto Breath

Individuals may experience a short-term change in their breath when they begin keto.

However, this is not a cause for concern but a reliable sign that they are in ketosis (Musa-Veloso et al. 200221).

The ketone body acetone causes the so-called keto breath. Many people say that smell of acetone reminds them of nail polish remover.

Because acetone is excreted through the breath, breath meters can be used to measure whether you are in ketosis.

However, few people pass so much acetone on their breath that it smells like nail polish remover.

Keto breath can only occur at the beginning of the keto diet when the body is not yet using the ketones efficiently. Therefore, it does not last long.

7. Mental Clarity

The last side effect is why I have not stopped keto for years.

A ketogenic diet increases BDNF, the brain-derived neurotrophic factor (Hu et al. 201822).

BDNF is a neuronal growth hormone responsible for the formation of new neurons. High BDNF levels are associated with increased intelligence, mood, and memory.

Many people, like me, report that they can think more clearly in ketosis.

In addition, recent studies suggest that ketones are fundamentally better energy sources for our brains (Prins et al. 201423).

Once your body is fat-adapted, you, too, will notice a significant increase in your energy levels.

How to Avoid Keto Side Effects

Switching from a Standard American Diet (SAD) to a keto can be challenging. However, adverse side effects are gone once the body efficiently uses fat as its primary energy source.

But you don’t have to let it get that far. With these three simple tips, most people can avoid unpleasant side effects when starting keto:

  1. Hydrate to counteract fluid loss during the first few days
  2. Salt as you go to prevent headaches, dizziness, and keto flu
  3. Embrace healthy fats like grass-fed butter or virgin coconut and olive oil

Adverse Side Effects of Keto Are Temporary

When the body relearns to burn fat instead of sugar, this is a massive change in metabolism. Side effects can occur during this process.

The good news is that most harmful side effects of the keto diet are not permanent. After one day to two weeks, they’ll be over. After three to six weeks, you’ll be entirely fat-adapted.

In short, your metabolism has gained flexibility and can now burn fat incredibly efficiently.

You might experience the keto flu if you don’t skimp on salt and water from the start. Flushed-out sodium is responsible for 99% of all physical side effects during the transition to ketosis.

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Keto Side Effects FAQ

What are the negative effects of a keto diet?

If you do not consume enough salt and water, you might experience headaches, fatigue, or nausea within the first days of keto.

How long do side effects of keto last?

Common side effects of keto usually last a few days to two weeks at max.

Is keto diet healthy or harmful?

Research confirms that ketogenic diets are a safe way to lose weight without noticeable side effects, especially over extended periods.



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Mag. Stephan Lederer, MSc.

Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.

Stephan is a true man of science, having earned multiple diplomas and master's degrees in various fields. He has made it his mission to bridge the gap between conventional wisdom and scientific knowledge. He precisely reviews the content and sources of this blog for currency and accuracy.

Click on the links above to visit his author and about me pages.

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