Getting into ketosis is a tremendous change for the body. After all, it has been working mostly on carbohydrates for decades on end and suddenly — the carbs are gone, replaced by a huge amount of dietary fats.
To keep on functioning, your body’s metabolism has to switch from getting its energy from carbs to fats, and that’s what explains everything you may feel during your ketoadaptation.
Changes in carbohydrate metabolism
First of all, your body will break down most of its glycogen — a special form of glucose that your body creates to store carbs in case you’ll ever be starving. Most of the body’s glycogen reserves are located in the liver and muscles.
The break down of glycogen stores in the muscles results in a temporary state of general fatigue and lethargy. When the liver glycogen stores are used up, some people report headaches, ”brain fog,” dizziness, impaired concentration, and everything else that’s considered to be part of the Keto Flu.
Note that not all people actually feel these changes: some folks have amazing adaptive potential, switching from carbs to fat for fuel almost immediately.
Now, if the carb restriction persists and most of the carbohydrate stores are used up, the body changes its metabolism of fat.
Changes in fat metabolism
The human body has an alternative pathway of getting energy in case of significant carbohydrate restriction: transforming fatty acids into ketone bodies. This process takes part in the liver, mainly after the organ’s glycogen stores are depleted (within the first 24 hours of carb restriction).
Skipping most of the molecular details, here’s what the whole process looks like:
1. Fatty acids are mobilized from body fat and dietary sources into the liver cells
2. Inside the liver cells, the fatty acids enter the mitochondria (the ”power plants” of the cells) and are transformed into 3 types of ketones: acetoacetate, beta-hydroxybutyrate, and acetone
3. These ketones are released into the blood and transported throughout the body
4. All organs and tissues use ketone bodies up as a source of energy
In the list above, the first point is what explains the weight loss during keto: basically, your body just starts burning its fat reserves for energy. The last point accounts for the often reported improvements in concentration, focus, motivation, and general cognitive performance after ketoadaptation: for the human brain, ketone bodies are much more effective as a source of energy than glucose.
Changes in water and salt balance
Another major change you will experience during your ketoadaptation is significantly increased urination. Some people try to explain this by stating that ketones have a diuretic effect, but that’s not true: it’s all due to the breakdown of glycogen.
Every gram of glycogen in the body binds 2.7-4 g of water, and the average person has about 100 g of glycogen stored in the liver and another 500 g in the skeletal muscles. When all of it is broken down during the first days of going keto, you will lose somewhere around 1620-2400 ml of water!
More importantly, remember that you will lose quite a lot of mineral salts via increased urination. Altogether, such a sudden loss of water & salts may result in constipation, dry skin, heart palpitations, and muscle cramps — so prepare beforehand and do your best to minimize the effect.
Specifically, it’s recommended to significantly increase your water intake, especially during the first two weeks of going keto. Aim to get about 2-3 l (68-100 ounces) of water daily, but don’t make this an obligatory thing: listen closely to your body and rely on your thirst. Also, make sure to eat enough table salt to compensate for the loss of sodium and include a lot of potassium-rich foods to restore your potassium levels. Some keto-friendly potassium-rich foods are:
However, remember that in order to effectively reach ketosis it’s recommended to limit your daily carb intake to 35 g or even less.
Reaching nutritional ketosis and maintaining it is a dramatic change for the human body, so it’s just natural to experience all sorts of changes during this adaptation period.
Brain fog, lethargy, fatigue, weakness, significant loss of water and salts… But don’t panic! Everything of the listed above is part of a natural and controlled process that will last a week at most, rarely two. As soon as your body is used to its new fat-fueled self all unpleasant sensations and changes will cease, giving place to all the outstanding benefits of a life on keto.