Ketosis vs. Keto-adapted (fat-adapted)

This is definitely one of the more frequent questions asked amongst beginners in the world of keto. What is the difference between being in ketosis and being keto-adapted or fat-adapted? The answer is both simple and complex. The two are not mutually exclusive although one can live without the other and vice versa, at least briefly. What that means is you can be in ketosis and not be fat-adapted, and you can be fat-adapted and not be in ketosis. Stay with me now. It might be more helpful to say that ketosis is the means by which you become fat-adapted.

What is ketosis?

Ketosis is actually a pretty normal state and occurs quite often in the body without people even realizing. When your system runs out of glucose, you start breaking down fat cells and using them for energy. The released fat travels through the body to the liver where it is turned into ketones. These ketones are then returned to the blood where they are carried to muscle and other tissues and used for fuel. While this process is occurring, you are in ketosis.

Ketones are acids, and while a moderate level of them in your blood is perfectly safe, a high level can cause ketoacidosis which can be extremely dangerous. Ketoacidosis occurs when there are too many ketones in the bloodstream making the blood too acidic.  This condition is common in diabetics because their system cannot produce enough insulin to balance the level of ketone production. This is not to be confused with nutritional ketosis which is completely healthy and highly beneficial. Being in nutritional ketosis as brought on by a low carb/high fat diet will absolutely not cause ketoacidosis.

How quickly you progress into ketosis depends on the individual. Some people can get there in as little as a day or two, others can take up to a week. Usually it’s around 4-5 days to really start to adjust. Sometimes while your body is adjusting to its new low carb life, you may experience what’s known as the “keto flu“. This is just a side effect of detoxing from carbs and processed foods, and it will pass. Ensuring proper electrolyte balance does wonders for curbing the keto flu. 

Most people go about 12 hours overnight without eating. During this time, your glucose has been depleted and you wake up in a mild state of ketosis. This is the reason some people choose to intermittent fast (IF) upon waking to take advantage of this natural ketosis. It forces your body to continue to use stored fat as opposed to any fat you may ingest during a morning meal. Be cautious with IF, it is only meant as a temporary tool and it should occur naturally. If you are hungry, you need to eat.

Many people use products that test for ketones in the blood, breath, or urine. They are supposed to tell you when you are in ketosis. Personally, unless you are on a restricted ketogenic diet for medical reasons, I really don’t understand the fascination with these. If you track your macros, and keep your carbs under 20 grams per day, you are going to be in ketosis. It may take a few days to a week to get there, but you’ll get there. The testing products can become expensive and they are not always an accurate representation of what’s going on in your body. They really only measure the amount of unused ketones being excreted by your body and not necessarily whether or not you are in ketosis.

What is keto-adapted?

Keto-adapted, or fat-adapted, is the state in which the body no longer prefers to use glucose or carbs for fuel but rather fat. This is actually how nature intended our bodies to operate. Long ago, when mankind was just getting started, there were no processed foods and people weren’t harvesting grains or other crops to make food. We ate meat, and whatever local fruits and vegetables were available. Even when we did start to eat bread-like products, they weren’t sugar and carb laden crap like they are today.

In the 1700’s, human consumption of sugar was around 4 pounds per year, or 1% of our total caloric intake. By 1800, it was around 18 lbs and by 1900 it was 60 lbs per year. In 2009, it was estimated that Americans consumed almost 180 lbs of sugar per year. So, we eventually evolved into a race of sugar-burners and that’s where a lot of the modern-day health issues began. Making the switch to a low carb/high fat diet such as keto, is simply getting our bodies back to the state in which they were always meant to operate.

After a prolonged period of steady ketosis, your body figures out that it’s not going to get the carbs it’s been relying on for so long, and actually reconfigures itself to use fat for fuel. You are no longer in the adjustment phase but rather you have settled into your new way of life. This process can take weeks or sometimes longer depending on the individual, but it will happen.

There is no real way to test if you are keto-adapted but there are plenty of ways to tell by simply observing changes in your life and how you feel. Some of the biggest indicators are:

  • “Brain fog” diminishes significantly. There are a number of reasons that contribute to a more clear mind on keto. Insulin spikes can really screw with your hormone balance. When this is kept in check, you feel much more even-tempered and are able to think more clearly. Also elevated ammonia and depressed GABA levels in the brain have a negative effect on mental clarity. Keto both increases GABA and helps to mop up extra ammonia.
  • Energy levels even out and usually increase from their pre-keto levels. Instead of the roller coaster rise and fall of energy that accompanies a carb filled diet, fat burners enjoy a steady stream of fuel regardless of when they’ve eaten last. Many report going well into the afternoon before realizing they haven’t had anything to eat that day.
  • General feelings of calm, even euphoric like moods are not uncommon. As you move through your day without hunger cravings or energy drops, you are much better equipped at handling whatever gets thrown your way without losing your cool or getting stressed.
  • Workouts seem a lot easier and there’s no longer the need to “carb load”. As a runner, I can personally attest to the fact that I can run farther and longer with little or nothing to eat prior.

In general, you can just feel your body running more efficiently. For me, being 45 years old and having to chase a toddler around, this was a game changer. I have more energy overall than when I was in my 20’s. And besides the “mom brain” that is relatively unavoidable, I definitely find myself to be more clear-headed and happier in life.

Hopefully, this answers some basic questions about the differences between being in ketosis and being keto-adapted. Feel free to leave any further questions you may have in the comments below.

Thanks for reading!







  1. Can your ketones be too high if you are fat adapted? Sugar levels are in the optimal range.

    1. Hi Darwin, sorry for the delayed response. I assume you mean when testing your ketone level. If you are doing keto properly, your ketones should never be too high. The pee sticks only show excess ketones in your system and are not necessarily indicative of ketosis. The levels vary from day to day but should never be too high. If, however you are testing extremely high on a regular basis, you need to speak with your doctor. This could be ketoacidosis and a symptom of blood sugar issues. Nutritional ketosis does not cause ketoacidosis.

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