Think of your body’s energy supply as a three-storied warehouse. The first floor is occupied by circulating glucose, the second by the glycogen in your liver and muscles while fat stores inhabit the last floor. With carb restriction, your body first uses the reserves on the first floor, making its way down slowly to the last floor. When you eat high-carb diets or sugar, your body rarely needs to go hunting to the last level for energy. It doesn’t budge beyond the first level of glucose. Intermittent fasting and carb restriction amongst others ways can help your body to adopt the reverse bottom-up approach and use the fat stores on the last level. This is how fat-adaptation works.
Highlights
- Metabolic flexibility is the body’s ability to process fuel from either source of energy—fat or glucose,
- Fat adaptation is the body’s acclimatisation to ketosis. What is ketosis? It’s a process that unfolds when there is a dearth of carbohydrates in the body to burn for energy and the body burns fat as the dominant source of energy,
- Relying more on fat for energy during exercise allows us to store glycogen for when we really need it. Being able to mobilise and oxidise stored fat during exercise can reduce your dependence on glycogen, amid its other health benefits. Fat adaptation in short is tied to effective glucose control.
Metabolic flexibility is the body’s ability to process fuel from either source of energy—fat or glucose. It has been documented that athletes who are fat-adapted, meaning those who rely on fat instead of carbs to burn energy, can potentially perform better or have greater endurance for more intense, longer-workout sessions. Here, we understand how fat adaptation works in your body and sift the fact from the fiction.
What is fat adaptation?
Fat adaptation is the body’s acclimatisation to ketosis. What is ketosis? It’s a process that unfolds when there is a dearth of carbohydrates in the body to burn for energy and the body burns fat as the dominant source of energy.
The keto diet, which has gained popularity recently, spurs ketosis. A diet low in carbs and high in fat puts the body in ketosis after a few days of following it. In this state, the body breaks down fatty acids to form ketone bodies, defined as water-soluble molecules produced by the liver from fatty acids and oxidised for energy.
‘Fat-adapted’, in this case, means that the body has reached a state in which it can burn fat for energy more effectively. This effect is still being researched.
To be and stay in the state of ketosis, you would normally eat no more than 50—and sometimes as few as 20—carbs per day for several days. Ketosis can often also occur during periods of starvation, infancy, pregnancy or fasting. Being fat-adapted can start any time between 4–12 weeks after the body enters the state of ketosis, depending on the specific individual and how strict they are with the diet. Endurance athletes may adapt even sooner.
For those who don’t follow the keto diet, burning carbs is known as being carb-adapted. Most people, though, will end up naturally following non-keto diets and can be considered carb-adapted, even though their bodies use a mixture of carbs and fats. The ketogenic diet allows the balance to be shifted in favour of fat burning. This can be observed in athletes who follow the keto diet for up to 2 weeks and then immediately restore carb intake before an event. Fat adaptation in non-athletes has not yet been studied.
How fat adaptation differs from ketosis
Being fat-adapted doesn’t mean you’re automatically in ketosis all the time. Ketosis involves the use of fat-derived ketone bodies by tissues, such as parts of the brain, that normally use glucose. This usually happens after you’ve depleted your glucose stores and the body starts producing ketones for energy. Ketones in your bloodstream indicate a state of ketosis.
Fat adaptation is a longer state of ketosis in which consistent energy is derived from fat. This state is expected to be more stable as the body has transitioned to using fat as its main energy source. In the initial stages of the keto diet, a sudden carb increase can throw you out of that state, as the body prefers to burn carbs.
Benefits of fat adaptation
1. Fat adaptation and glucose levels
A ketogenic diet informs the body that very little glucose is available in the environment, which results in impaired glucose tolerance and insulin resistance. On the other hand, a well-constructed lower-carb diet that leads to weight loss can improve insulin sensitivity.
2. Decreased cravings
Keto enthusiasts cite a study in which 20 middle-aged adults with obesity were placed on a controlled, phased diet for 4 months. The ketosis in the study resulted from keto along with a very low-calorie diet.
The initial diet, which had only 600–800 calories per day, went on until each participant had reached their target weight. Peak ketosis lasted about 50–90 days and food cravings were reported to drop significantly over the course of the study.
3. Better sleep
This study found that 14 healthy men who were on a ketogenic diet experienced better sleep but reduced rapid eye movement (REM) sleep. REM sleep is considered important since it operates the brain centre that facilitates learning.
However, some studies suggest that these effects are limited to specific groups like children and teens with morbid obesity or ones who have sleep disorders. More research is needed in this sphere.
4. Fat loss
Relying more on fat for energy during exercise allows us to store glycogen for when we really need it. Being able to mobilise and oxidise stored fat during exercise can reduce your dependence on glycogen. This is the quintessential – ‘train low, race high’ situation. It helps to improve performance, saving glycogen for the truly intense moments of a training session and end up actually burning more body fat. If you can handle exercising without having to fuel with carbs, you’re probably fat-adapted, and if you can work out well in a fasting state, you’re definitely fat-adapted.
5. Steady energy
Being fat-adapted is considered the ideal state for humans. It’s easy to forget this when we’re constantly being bombarded with carb- and sugar-laden treats. The way the human body has evolved allows it to run far better on ketones and stored body fat. When we’re fat-adapted, we can access the primal metabolic state and enjoy its benefits. One of the primary benefits is steady energy. Carbs are a less efficient energy source than fat, and eating them can result in feeling sluggish or slower. Having sustainable, steady levels of energy that don’t require a caffeine fix and which don’t experience a crash after is one of the greatest signs and rewards of being fat-adapted.
6. Mental performance
The ketogenic diet was initially devised to treat children with drug-resistant epilepsy since children have a greater capacity to use ketone bodies for energy as compared to adults.
One molecule present in the ketone bodies called beta-hydroxybutyrate (BHB) has been shown to protect the brain. The exact reason for this is not clear but the effect of BHB on the brain explains the long-term focus ketogenic enthusiasts and dieters experience.
7. Endurance capacity
Studies show that athletes perform better in nearly every way when they’re on low-carb diets. Low-carb athletes burn more fat while doing the same exercise as the ones who are loading up on carbs; they also end up using oxygen more efficiently and can work out for longer. It takes some time to get used to being low-carb but your endurance will increase considerably when you’re fat-adapted. Some contradictory research suggests that effective control of glucose levels with carbohydrate consumption and increasing glucose availability minus the sharp sikes enhances performance by more than 60%, lending credence to the necessity of adequate pre-exercise and in-exercise glucose intake.
Ways to become fat-adapted
1. Eat a low-carb diet:
The first step would be to restrict carbs since that keeps the blood sugar and insulin levels low, and low insulin levels can signal to your liver to start burning fat and making ketones. The carb tolerance of a person will depend on their activity level. The more active someone is, the more carbs they can eat and stay fat-adapted. A keto diet is a popular approach but it’s not the only way. A paleo-style approach (also known as the caveman diet) that restricts carbs to 50–100 grams daily can also work. Steering clear of sugar is important in achieving a state of fat adaptation.
2. Eat more fat:
As the carbs decrease, you’ll want to increase dietary fat; that’ll train your cells to run on fat and will have a smaller impact on insulin levels as compared to carbs. A low insulin state allows you to stay in fat-burning mode instead of fat-storage mode. Consume healthy fats like olive oil, coconut oil, nuts, avocados, butter and animal fat to constitute about 50–75 percent of your daily calories, along with adequate protein. You can use the calories in fat as a way to build, maintain or lose body mass. That being said, remember you can’t be consuming unlimited fat. As fat intake goes up, calories need to go down too.
3. Fasting:
When you haven’t eaten for a while, the body derives energy from carbs, yes, but the glucose reserves get used up quickly since the liver and muscles only hold up about 500 grams. The body can’t use protein from muscle tissue since losing significant lean mass on a temporary fast is not ideal. Accessing body fat through fasting is a valuable tool in the fat-adaptation manual.
4. Exercise:
Exercise alone doesn’t help in making you fat-adapted but it makes the process much easier. Strength and endurance exercise has been proven to increase insulin sensitivity. Higher insulin sensitivity is linked to faster fat burning after carbs. High-intensity interval training (HIIT) through sports like CrossFit, tennis, etc., is a good way to achieve this.
Conclusion
Fat adaptation, or the ability of our bodies to rely on fats as the main fuel source instead of carbs, is the preferred metabolic state for humans. It’s nothing extraordinary—it just means we’re meant to fuel ourselves. That’s why we have the fat we have on our bodies, and it’s believed to be a fairly reliable source of energy. The benefits of being fat-adapted are experienced in the form of fat loss, steady energy, endurance capacity, better mental performance, decreased hunger and cravings and improved sleep. The ways to become fat-adapted include fasting, consuming fewer carbs, eating more fat and exercising, preferably in the form of HIIT workouts.
Disclaimer: The contents of this article are for general information and educational purposes only. It neither provides any medical advice nor intends to substitute professional medical opinion on the treatment, diagnosis, prevention or alleviation of any disease, disorder or disability. Always consult with your doctor or qualified healthcare professional about your health condition and/or concerns and before undertaking a new healthcare regimen including making any dietary or lifestyle changes.
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