Ketosis is a metabolic state that occurs when your body burns fat for energy instead of glucose. The keto diet has many possible benefits including potential weight loss, increased energy and treating chronic illness. However, the diet can produce side effects including “keto” breath and constipation.
Ketosis is a process that occurs when your body uses fat as its main fuel source. Normally, your body uses blood sugar (glucose) as its key energy source.
You typically get glucose in your diet by eating carbohydrates (carbs) such as starches and sugars. Your body breaks the carbohydrates down into glucose and then uses the glucose as fuel. Your liver stores the rest and releases it as needed.
When your carb intake is very low, these glucose stores drain down. Since your body doesn’t have enough carbs to burn for energy, it burns fat instead. As your body breaks down fat, it produces a compound called ketones. The ketones, or ketone bodies, become your body and brain’s main source of energy.
The fat your body uses to create ketones may come from your diet (nutritional ketosis), or it may come from your body’s fat stores. Your liver produces a small amount of ketones on its own. But when your glucose level decreases, your insulin level decreases. This causes your liver to ramp up the production of ketones to ensure it can provide enough energy for your brain. Therefore, your blood has high levels of ketones during ketosis.
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The ketogenic (keto) diet changes the way your body uses food. Typically, carbohydrates in your diet provide most of the fuel your body needs. The keto diet reduces the number of carbs you eat and teaches your body to burn fat for fuel instead.
The keto diet is high in fat, moderate in protein and low in carbohydrates. The standard keto diet consists of 70% to 80% fats, 10% to 20% proteins and 5% to 10% carbohydrates.
Many nutrient-rich foods contain high amounts of carbohydrates. This includes whole grains, fruits and vegetables. Carbs from all sources are restricted on the keto diet. So you’ll have to cut out all bread, cereal and other grains and make serious cuts to your fruit and vegetable intake. The types of foods that provide fat for the keto diet include:
You’ll need to stay under 50 grams of carbohydrates per day to enter and stay in ketosis. That’s about three slices of bread, two bananas or 1 cup of pasta.
If you eat between 20 and 50 grams of carbohydrates each day, it will usually take you two to four days to enter ketosis. However, the time it takes to enter this state varies based on several factors. It may take you a week or longer to get into ketosis. Factors that may influence how long it takes you to achieve this state include your:
If you eat a high-carb diet before starting a keto diet, it may take you longer to reach ketosis than someone who consumes a low-carb diet. That’s because your body needs to exhaust its glucose stores first.
You may be able to get into ketosis faster with intermittent fasting. The most common method of intermittent fasting involves eating all of your food within eight hours. Then, you fast for the remaining 16 hours of a 24-hour period.
Research has shown that ketosis may have several health benefits. One of the biggest benefits of ketosis may be weight loss. The process can help you feel less hungry, which may lead to eating less food. It can help you lose belly fat (visceral fat) while maintaining a lean mass. Other possible benefits of ketosis include treating and managing diseases such as:
Ketosis has also been shown to increase your focus and energy. The keto diet delivers your body’s energy needs in a way that reduces inflammation. Research suggests your brain works more efficiently on ketones than on glucose.
The keto diet has many benefits, but it may come with some side effects. One of the signs of ketosis may include “keto flu,” which includes symptoms such as upset stomach, headache and fatigue. Other symptoms of ketosis may include:
Ketosis and diabetes-related ketoacidosis (DKA) are two very different things. During ketosis, you have ketones in your blood but not enough to turn your blood acidic. It usually happens if you’re fasting or following a low-carbohydrate diet. Ketosis isn't harmful.
DKA is a condition that affects people with diabetes and people with undiagnosed diabetes. It happens when your blood turns acidic because it has too many ketones due to a lack of insulin. Diabetes-related ketoacidosis is life-threatening and requires immediate medical attention.
A note from Cleveland Clinic
Ketosis is a metabolic state that occurs when your body burns fat for energy instead of glucose. The keto diet has many possible benefits. These include potential weight loss, increased energy and treating chronic illness. However, the diet can be difficult to follow and can produce side effects including “keto” breath and constipation. If you’re interested in the health benefits of ketosis, ask your provider if the diet may be right for you.
Last reviewed by a Cleveland Clinic medical professional on 08/15/2022.
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