Ketogenic Diet (keto) - Contraindications and Side Effects

The ketogenic diet is an increasingly popular method of losing weight and shedding body fat. However, not everyone considers its contraindications before starting.

The basis of the keto diet is to increase fat consumption and moderate protein consumption, while carbohydrates are limited to the maximum.

Before starting this diet and entering ketosis, we recommend reading the contraindications in detail.

This article describes the contraindications and side effects of the ketogenic diet with supporting evidence.

Contraindications of the ketogenic diet

The keto diet is contraindicated for pregnant women, as it is not allowed for people with diabetes with uncontrolled blood glucose levels.

It is also not recommended for adolescent children or those with digestive problems, stomach ulcers, or gastritis. A lack of fiber foods on the keto diet can slow down the digestion process and aggravate symptoms. The contraindications of the ketogenic diet are:

  1. Pregnant women
  2. People with pancreatitis
  3. People with a lack of carnitine
  4. Disorders in the cardiovascular system
  5. People with high cholesterol
  6. Children and adolescents (except in cases of epilepsy)
  7. People with type I diabetes

Why can the ketogenic diet hurt?

The contraindications and consequences of the ketogenic diet are due to changing the percentage of macronutrients. On the keto diet, fat intake increases, proteins are the secondary macronutrient, and carbohydrates are limited to the maximum.

The percentage of macronutrients in a ketogenic diet are (1):

  • 75-80% fat
  • 10-15% protein
  • 5-10% carbohydrates

According to the WHO and the FAO, in a healthy diet, the percentages of macronutrients should be (2) (3):

  • 55-60% carbohydrates
  • 30% fat
  • 15-20% proteins

Side effects of the ketogenic diet

Like other low-carbohydrate diets, the ketogenic diet is contraindicated for people who take blood pressure medications, have the fatty liver syndrome, high levels of bad cholesterol, and blood triglycerides.

The risk of side effects increases in children and adolescents, as their bodies are more susceptible. The main side effects of the ketogenic diet are:

  1. Impairment of the nervous system

Some studies (4,5,6) have verified a deterioration of the nervous system after carrying out a ketogenic diet. The power of attention is diminished, and memory speed and the processing of images and information. Therefore, one of the ketogenic diet contraindications is for those who work with heavy machinery or driving.

  1. Bad breath

Bad breath is one of the most well-known contraindications of the ketogenic diet. By basing a diet on ketogenic foods, the body uses ketone bodies as an energy source; these compounds give off an unpleasant odor similar to acetone.

  1. Lack of vitamins and minerals

The second contraindication of the ketogenic diet is the lack of vitamins and minerals. The carbohydrate foods like fruits and vegetables are the highest in this type of nutrients. In the ketogenic diet, a lack of iron, calcium, magnesium, and potassium is common.

  1. Digestion problems

A third side effect of the ketogenic diet is digestion problems. By basing the diet practically on fatty foods and especially by reducing foods with fiber, the functioning of the digestive system can be disturbed. One of the contraindications is for people with constipation problems.

  1. Increase in bad cholesterol

A study comparing the effects of a low-calorie diet high in complex carbohydrates and a keto diet high in nuts. The second obtained 60% better results in weight loss. The bad news – is lousy cholesterol levels rose. (3)

  1. Kidney disorders

The ketogenic diet is strictly contraindicated for people who have had some kidney disorder. One of the strategies to avoid the side effects of this diet is not to extend a period longer than 6 – 12 months. (1)

  1. Increased likelihood of cancer

This is considered the worst of the contraindications of the ketogenic diet. However, it does not apply to all versions of this diet but to those where red and processed meats predominate—the WHO has declared these foods as type II carcinogens.

How do we minimize the side effects of the ketogenic diet?

The minor side effects can be accentuated in the first few days of the ketogenic diet. This period of adaptation is known as the keto flu.

You are likely to experience low energy,  sleep disturbances, increased hunger, frequent urination, dry lips, constipation, and nausea when viewing stomach foods. Also, if you are an athlete, you may feel less strength when training. To minimize the side effects of the ketogenic diet, you can:

  • Increase the amount of salt in meals
  • Drink more water (2.8 L of water per day)
  • Take magnesium (300 mg per day) and potassium (1000 mg per day) supplements
  • Eat more vegetables and low-carb fiber foods for constipation
  • take melatonin to sleep
  • Lip sunscreen for dry lips
  • If the effects persist – Go on a less strict low-carb diet for a few days


The ketogenic diet is a low-carb diet with rapid effects on weight loss.

Although its effects are faster than other diets, it is not the healthiest method to lose weight.

The side effects of the keto diet can bring long-term complications to the digestive, nervous and cardiovascular systems.

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