Keto diet

Ketosis: Definition, Symptoms And Side Effects Of Keto Diet

Ketogenic diets are very popular for weight loss. In this article we discuss the pros and cons of ketosis.

Whenever we are looking for ways to lose weight, the terms 'keto diet' and 'ketosis' appear. They are described as a regular metabolic process, although it is not clear whether this type of diet is good or bad for our health.

The answer to this question is not easy, for there are many people that are for and against it. In this article, we will discuss what this type of diet is, its symptoms and possible side effects.

What is ketosis?

Ketosis is a metabolic state in which part of the body's energy supply comes from the ketone elements of the blood, compared to the usual metabolic state in which energy comes from glucose in the bloodstream.

When on a keto diet, the body metabolizes fat at a very fast rate and converts fatty acids into organic compounds called ketones.

This is a normal metabolic process, something that our body does in order to continue working when it does not have enough carbohydrates from food. As a consequence of this lack, our organism obtains energy from fat, burning it and producing these ketones.

In a healthy person who has a balanced diet, the body controls the amount of fat it burns and does not usually produce or use ketones. However, when we start a keto diet, we reduce the intake of calories or carbohydrates, and our body goes into a state of ketosis for energy.

This process can also occur after exercising for a long time or during pregnancy, and although a controlled proper keto diet is not necessarily harmful, ketosis can become dangerous  when too many ketones accumulate.

These high levels of ketones lead to dehydration and can change the chemical balance of the blood, leading to ketoacidosis. Ketoacidosis is a condition in which over-accumulation of ketones can be life-threatening and requires urgent medical attention.

The most common type is diabetic ketoacidosis, in which both glucose and ketone levels are significantly elevated.

Keto diet

Starting a keto diet to getting into a state of ketosis is a very popular weight loss strategy. Ketogenic diets and low-carbohydrate meal plans emphasize protein intake to feed our body.

In addition to promoting the burning of fats, this type of diet is characterized by its satiating effect and by helping the proper maintenance and health of muscles.

On the other hand, some research suggests that the keto diet may help reduce the risk of heart disease, while others indicate that specific very low-carbohydrate diets may help people with metabolic syndrome, insulin resistance, and type 2 diabetes.

In healthy people (except for pregnant women), ketosis usually begins about 3 to 4 days after eating less than 50 grams of carbohydrates a day. To maximize the benefits of this diet, decrease the possible risks and side effects and learn to follow it properly, it is necessary to consult and follow the instructions of a nutrition professional.

Getting into ketosis: Symptoms

During ketosis, our body undergoes many biological adaptations, including a reduction in insulin levels and further breakdown of fats. When this happens, our liver begins to produce more ketones to supply energy to our brain.

However, it can sometimes be difficult to know whether we have reached this state or not. If we have, we may experience the following symptoms, some positive and some negative:

1. Weight loss

A keto diet, along with a low-carbohydrate diet, is often very effective in losing weight.

Short- and long-term weight loss is characteristic of a ketogenic diet. At first,  the results are very obvious because of the decrease in stored carbohydrates and water being wasted.

2. Appetite suppression

Many people report a significant decrease in appetite while on a keto diet.

Studies suggest that this is because of the increased consumption of proteins and vegetables, coupled with an alteration of the hormones in our body that are responsible for regulating hunger.

3. Increased energy

People often experience a feeling of tiredness and mental confusion or discomfort when starting a low-carbohydrate diet. In the long term, however, this often translates into increased energy and even greater concentration.

When we get into ketosis, a large part of our brain begins to consume ketones instead of glucose and our body may need to adapt to these changes.

Ketones are a very potent source of fuel for our brain, so it's no wonder that people on a keto diet report greater clarity and better long-term brain function.

4. Short-term fatigue

At first, switching to a ketogenic diet can be really hard, as the first symptoms can include fatigue and physical weakness.

This usually leads to the person abandoning the keto diet before getting into ketosis. However, these symptoms are normal and, although they usually disappear over time, can be compensated for by electrolyte supplementation.

5. Short-term decrease in performance

Along with fatigue, a decreased in physical exercise performance may also be experienced.

Primarily, this is due to the reduction of glycogen reserves, which provides the fuel source for high-intensity exercise.

After several weeks following the keto diet, most people report that their performance has returned to normal. Also, in certain endurance sports, the ketogenic diet may even be beneficial to sports performance.

Chica haciendo ejercicios gimnásticos de espaldas
Although it is very common among athletes, ketosis can occasionally lead to a decrease in physical performance in the short term | LND

6. Increased ketones in the blood

One of the most distinctive features of the keto diet is the decrease in blood sugar levels and an increase in the number of ketones instead.

As the diet goes on, more fats are burned and ketones become the main sources of fuel.

The measurement of ketones in blood is the most accurate way to know the levels of ketosis. This is done through a finger prick blood sample similar to a blood sugar test.

According to some studies, nutritional ketosis is defined as blood ketone levels ranging from 0.5 to 3.0 mmol/L in the blood.

Other ways to measure ketone levels is through a urine or breath test.

7. Digestive problems

Generally, the keto diet involves a major change in the types of food consumed. As a result, it is possible to experience digestive issues such as constipation or diarrhea at the start of the diet.

Some of them usually go away after a transition period, but it may be necessary to keep track of the foods that may be causing the problems.

The most important thing is to follow a varied diet. Otherwise, these issues may remain.

8. Bad breath

Many people often report the onset of bad breath once they get into complete ketosis. In fact, this is a very common symptom in which the breath smells fruity-like. This is caused by high levels of ketones, specifically acetone.

This can be a positive sign that a state of ketosis has been reached and can be compensated with proper oral hygiene.

9. Insomnia

Finally, one of the biggest problems for many people who follow this diet is insomnia, especially at the beginning. These people refer to problems falling asleep or waking up many times at night.

However, this usually improves in a few weeks and many of the people affected claim that they sleep better than before starting the diet.

Risks and side effects

Despite the potential benefits of ketogenic diets, health complications such as ketoacidosis may occur when ketosis reaches excessively high levels.

Ketones build up badly in the blood and become acidic, causing symptoms such as:

  • Thirst or dry mouth
  • Increased need to urinate
  • Feeling tired
  • Upset stomach
  • Vomiting
  • Difficulty breathing
  • Confusion

Ketoacidosis can be very dangerous, leading to coma or even death — hence the need to seek health care as soon as possible.



Manninen, A. H. (2004). Metabolic effects of the very-low-carbohydrate diets: misunderstood "villains" of human metabolism. Journal of the International Society of Sports Nutrition, 1(2): 7–11.

Paoli, A., Rubini, A., Volek, J. S. & Grimaldi, K. A. (2013). Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. European Journal of Clinical Nutrition, 67(8): 789–796.