Keto Adaptation: How Long Does It Take?

The keto-adaptation phase is the process by which the body transitions from using glucose for energy to using fat. This process can take anywhere from 30 days to 12 weeks, with some people experiencing the positive effects of keto-adaptation after about a week to 10 days. The first phase is carb withdrawal, which can last from 3 to 14 days and is characterised by cravings, hunger and the keto flu. The second phase, which can last from 6 to 8 weeks, is when the body adjusts from relying on glucose to fat for energy. After several weeks, the body is on fat-burning autopilot and will remain in this state as long as the keto diet is maintained.

The transition to keto can cause the keto flu, which may last from 3 to 14 days

The transition to a keto diet can be challenging for the body, and it is common to experience a range of side effects known as the "keto flu." The keto flu typically lasts from 3 to 14 days and is characterised by symptoms such as fatigue, weakness, lightheadedness, "brain fog," headaches, irritability, muscle cramps, and nausea. This initial phase, known as carb withdrawal, is followed by a second phase lasting 6-8 weeks, where the body adjusts from relying on glucose to fat for energy.

During the keto flu, it is important to eat plenty of fat and non-carb sources of fibre to stay full and reduce cravings for carb-laden foods. It is also recommended to avoid strenuous physical activity and stick to gentle exercises like walking and stretching during this time.

By the end of the second week or around three weeks, the body has usually adapted to using fat for energy, and hunger and food cravings decrease while stamina and vitality increase. At this point, the body continues to make subtle changes, such as becoming more protein-conserving, which can further reduce protein cravings. Athletes may also notice improved performance with less lactic acid buildup in their muscles during long training sessions, resulting in reduced fatigue and soreness.

Overall, the transition to a keto diet can be challenging, but the symptoms of keto flu typically subside within 3 to 14 days as the body adjusts to using fat for energy.

After the keto flu, the body starts to adjust to using fat for energy, which can take 6 to 8 weeks

The first phase, carb withdrawal, is marked by cravings, hunger, and the keto flu, and lasts for 3 to 14 days. The second phase can then last for 6 to 8 weeks, and this is when the body really starts to make the transition to burning fat for energy.

During this second phase, it is important to focus on clean whole foods and stick to a ketogenic diet without any cheats or deviations. This means eating a low-carb, high-fat diet, with a focus on healthy fats from sources such as coconut oil, MCT oil, avocados, and olive oil. It is also important to monitor your intake of high-quality protein.

By the end of the second phase, your body will be on fat-burning autopilot, and as long as you maintain a keto lifestyle, it will stay that way. You will know you have reached this stage when you can go 4 to 6 hours between meals without getting hungry, feel consistently energetic throughout the day, and can easily work out while remaining on a keto diet.

The entire keto adaptation process can take anywhere from 30 days to 12 weeks

The first few days of the keto diet involve a significant reduction in carbohydrate intake, which causes the body to burn through its remaining carbs and glycogen stores. This is followed by the initial phase of keto adaptation, known as carb withdrawal, which typically lasts between 3 to 14 days. During this phase, individuals may experience cravings, hunger, and symptoms of the "keto flu," such as fatigue, weakness, lightheadedness, and nausea.

The second phase of keto adaptation can last between 6 to 8 weeks. In this phase, the body transitions from relying on glucose to fat as its primary source of energy. This is when the majority of the adaptation process occurs, and by the end of this phase, hunger and food cravings are usually diminished, and stamina and vitality increase.

After the initial two phases, the body continues to make subtle changes and adjustments. For example, it becomes more protein-conserving, leading to decreased protein cravings. Athletes may also notice improved performance and reduced muscle soreness due to less lactic acid buildup during training sessions. These changes can take up to 12 weeks to fully manifest.

It is important to note that the keto adaptation process may be different for endurance athletes, who may adapt to the keto diet even sooner. Additionally, the process may be influenced by factors such as hormonal fluctuations and stress. Overall, the time it takes to fully adapt to the keto diet varies from person to person, and it is essential to trust the process and make adjustments as needed.

Endurance athletes may adapt to keto faster than non-athletes

The ketogenic diet has become popular among endurance athletes as a performance enhancer. The diet prescribes a significant reduction in carbohydrate intake, which facilitates physiological changes that promote the utilisation of ketones. This diet minimises the body's reliance on carbohydrates, which are stored in the body predominantly as glycogen in muscle tissue (300g) and liver tissue (90g), in addition to glucose in the bloodstream (30g). This amounts to roughly 1680 kcal of available energy from carbohydrates at any one time. As a result, endurance athletes need to replenish their glycogen stores every one to three hours during activity. This continual consumption redirects nutrients from exercising muscles to the gut to aid digestion, potentially leading to reduced exercise economy and digestive disturbances, which compromise the athlete's ability to maximise training and competition outcomes.

Research has shown that training with low muscle glycogen availability promotes molecular changes that enhance training-derived endurance adaptations. Furthermore, ketogenic diets have been shown to reduce lactate accumulation after exercise, contributing to enhanced recovery. Taken together, this evidence suggests that reduced reliance on carbohydrates via ketosis can produce beneficial results for endurance athletes.

In theory, if endurance athletes tolerate the ketogenic diet, they could achieve longer training periods with sustained energy levels and reduced need for refuelling, allowing them to maximise the aerobic benefits from training and competing. In fact, there is some evidence that, among highly trained individuals, benefits of the diet include a steady supply of energy for the body and brain during prolonged exercise and accelerated recovery time post-exercise.

However, there is not enough research to prove that the ketogenic diet increases performance. Evidence still clearly shows that a high-carbohydrate diet is more beneficial in improving performance outcomes.

The process of keto-adaptation (or fat-adaptation) is when the body changes from using primarily glucose for energy to using primarily fat. The "keto" part refers to ketones, which are water-soluble molecules that the liver makes when metabolising fats, particularly when carbohydrate intake is low. Ketones can be used for energy by most tissues in the body, including the brain, which cannot use unrefined fats as fuel.

The length of time it takes to adapt to a keto diet varies, but the process begins after the first few days. Then, after about a week to 10 days, many low-carbers suddenly start to feel the positive effects of keto-adaptation. By the end of the second week (sometimes up to three weeks), the body has usually accomplished the majority of its work in adapting to using fat for energy. After this, the body continues to make more subtle changes, and it can take up to 12 weeks for these changes to occur and for someone to fully reach ketosis.

Endurance athletes and heavy exercisers often can eat more than 50 grams of carbs and still stay in ketosis.

How to become fat adapted

Fat adaptation is a simple way of saying that you’ve taught your body to burn fat – rather than glucose – for fuel. To become fat adapted, slowly start reducing your intake of foods high in both carbs and sugars, and replace them with healthy fats and high-quality proteins. When you do consume carbs, consume foods with a high amount of dietary fibre. Eat healthy fats from coconut oil, MCT oil, avocados, and olive oil, and high-quality protein from grass-fed meat, seafood, and eggs.

Note that “slowly” is a key point here. Going from eating 100 grams of carbs to 10 overnight is extremely taxing on your body. Rather than cut carbs out cold turkey, which can cause negative effects including headaches, brain fog, nausea, and other symptoms known as keto flu, try a more moderate approach.

It generally takes from 30 days to 12 weeks of sticking to a keto diet to become fat adapted. During this time, you want to focus on clean whole foods and stick to eating a ketogenic diet without cheats or deviations.

First, you’ll experience the initial phase: carb withdrawal, which lasts anywhere from 3 to 14 days and is characterised by cravings, hunger, and perhaps the keto flu.

Then you’ll roll into the second phase, where your body is adjusting from relying on glucose for energy to relying on fat, which can last 6 to 8 weeks. After several weeks, your body is on fat-burning autopilot, and that’s where you’ll stay as long as you maintain a keto lifestyle.

Signs that you’re fat adapted

• Can go 4 to 6 hours between meals without getting hungry
• Feel consistently energetic throughout the day, without energy slumps or a rumbling tummy
• Can easily work out while remaining on a keto diet

Once keto-adapted, the body can easily transition in and out of ketosis

The keto-adaptation phase, or the transition to a ketogenic diet, can take anywhere from two to three weeks or longer. During this time, the body adapts to using fat and ketones instead of glucose as its main fuel source. The process begins after the first few days, and by the end of the second week, the body has usually accomplished most of its work in adapting to using fat for energy.

The benefits of being keto-adapted include decreased cravings, increased energy, and improved sleep. The body can go longer between meals without feeling hungry, and there is more stable energy throughout the day. Physical endurance is also increased, as the body can leverage fat instead of glucose for energy.

However, it is important to note that the transition in and out of ketosis is dependent on maintaining a keto lifestyle. Cheating or deviating from the diet can affect the body's ability to stay in ketosis. Additionally, other factors such as hormonal fluctuations and stress can also impact ketosis.

Frequently asked questions