Ketosis is a normal metabolic process that takes over following a ketogenic diet low in carbohydrates and provides numerous health benefits. At the same time, in the initial period, it could trigger some side effects, which with some important precautions can be easily managed and resolved in a rather short time.


How ketosis works

Ketosis is a metabolic state that occurs when the body enters a glucose deficiency, either due to a voluntarily reduced intake of carbohydrates as a result of a diet (such as occurs with a ketogenic diet ) or as a natural consequence of fasting, i.e. prolonged deprivation from food. Both lead to reduced insulin levels, causing fat cells to be freed from fat cells for energy. When this happens, the liver is flooded with fat, which largely turns into ketones; the alternative energy source to glucose.


Sometimes it happens that the metabolic state of ketosis is mistakenly confused with ketoacidosis. While ketoacidosis is a serious condition caused by uncontrolled diabetes, ketosis is a natural metabolic state.


During ketosis, large parts of the body and brain use ketones made from fat as fuel, instead of the glucose that is normally released into the body with carbohydrates.


As with any other change, even in the case of ketosis, although it is a natural condition of the body, the body needs a period of time to adapt to the “new fuel”, which is the burning of ketones instead of glucose.


Therefore, during the initial phase, many people experience some side effects of ketosis, which however dissolve in a short time.


Let’s see what are the most common side effects of ketosis and how to alleviate them:

The “keto-flu”

At the beginning of ketosis it may happen to encounter a set of symptoms, generally referred to as “flu due to the low carbohydrate content” or more simply “keto-flu”, so-called because they actually resemble the symptoms of the classic flu.

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Keto flu includes headaches, fatigue, low energy, and difficulty concentrating, increased hunger, sleep problems, nausea, and decreased physical strength during workouts.


To minimize the initial effects, it is advisable to start with a low carbohydrate diet, to allow the body to adapt to less and less glucose. By reducing carbohydrates gradually, you will arrive at ketosis without the body being particularly affected by the change.


The ketogenic diet can also modify the water and mineral balance of the body, so it may be useful to add more salt or specific mineral supplements, and in particular potassium and magnesium, to the diet.


At least in the beginning it is important to avoid limiting calories too much. Usually, a ketogenic diet causes weight loss without intentional calorie restriction. In other words, it is possible to eat until you are full, but by choosing only the right foods.

In any case, the symptoms of keto-flu still tend to subside after just a few days.



One of the most common side effects of ketosis is bad breath.


The halitosis effect is caused by acetone, a by-product of fat metabolism in the ketosis process, which the body also gets rid of in part through the breath.


Occasionally, in fact, even sweat and urine can take on this easily recognizable odor, often described as fruity and slightly sweet.


For most people, halitosis will go away within a few weeks.




In ketosis, some people may experience leg cramps. While they are usually a minor problem, they are never pleasant and can be quite painful.

Leg cramps in ketosis are generally linked to dehydration and mineral loss.

Glycogen, the storage form of glucose in muscles and liver, binds water molecules to itself. With reduced carbohydrate consumption and consequent glycogen deficiency, the amount of water and mineral salts in the tissues also decreases and is one of the main reasons why people who adopt a low carbohydrate diet initially lose weight very quickly.

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Constipation or diarrhea

All dietary changes can initially cause some digestive problems, as all changes require a small period of adjustment. So also the organism, in the case of a radical change in diet, needs to adapt to the new nutrition program, different combinations of nutrients and above all to the different fuel, in this case, the ketones.

Constipation is a very common side effect at the onset of ketosis. This is most commonly due to not getting enough fiber and not drinking enough fluids.

Conversely, some people may initially experience diarrhea, but it is much less common.

In any case, as soon as the adaptation period is over, digestive problems also disappear; this usually clears up in the first few weeks of starting the diet.



Some people experience an increase in heart rate during the first few weeks of starting a diet as a side effect of ketosis. However, it is a rather common symptom, due to general dehydration caused by an always lower presence of glycogen in the tissues, as well as an insufficient salt intake.


It is certainly a good rule to drink at least two liters of water a day to maintain the right degree of hydration and, especially initially, to increase the amount of salt. These small tricks will greatly help to limit the increase in heart rate, which should normalize in a short time.


If the problem persists, it may be necessary, at least for a period, to increase the amount of carbohydrates in the diet.


Uncommon side effects:

  • Diabetic ketoacidosis, a severe acute condition that occurs in uncontrolled diabetes, typical of type 1 diabetes mellitus, has been found in some women who have recently given birth, probably triggered by a diet that is too low in carbohydrates, insufficient to meet the body’s primary needs while breastfeeding. However, this effect is extremely rare.


  • Kidney stones:  Although uncommon, some children with epilepsy have developed kidney stones following a maximized ketogenic diet.
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  • Elevation of cholesterol:  some adults during the diet have found an increase in cholesterol levels linked to low-density lipoprotein (LDL), so-called “bad”. This could be related to the amount of saturated fat consumed with meals. However, recent research has raised several doubts regarding its negative function in the body.



And finally, some general tips to minimize any side effects during the early period of ketosis:

  • Start with a moderate carb diet:

Before embarking on the ketogenic diet, start with a diet moderating carbohydrates, progressively lowering the amount to facilitate the transition and allow the body to gradually adapt to the new diet.


  • Drink lots of water:

Make sure you drink at least 2 liters of water every day to compensate for the natural dehydration caused by the loss of a significant amount of water due to glycogen deficiency, which occurs especially at the beginning of ketosis. In fact, it is very common to suffer from a constant feeling of thirst during the period of adaptation to ketosis.


  • Get enough salt:

Levels of sodium, a vital electrolyte, tend to drop due to their increased excretion via urine in correlation with reduced carbohydrate intake. It is sufficient to add a small larger amount in meals.


  • Integrate some minerals:

With the loss of water, the mineral levels in the body also tend to decrease. By consuming foods containing higher amounts of minerals, especially magnesium and potassium, you can prevent or relieve any muscle cramps.


  • Consume enough fiber:

Be careful to get enough fiber in your diet daily to remedy any digestive problems such as constipation or diarrhea. Choose low-carb vegetables, nuts, almonds, and various seeds.


  • Avoid strenuous exercise:

Try to moderate physical exertion in the first week or two as you adjust to ketosis.


In short, greater amounts of water, salt, minerals and fiber greatly alleviate the disorders that could occur at the beginning of ketosis when starting a ketogenic diet. By adding a gradual reduction in carbohydrates, the body will have plenty of time to adapt to the new diet, reducing any negative effects.

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