Is Fat Adaption Real?

At the most basic level, fat adaption refers to the process of transition where the body switches from relying on using carbohydrates as its main fuel source to ketone bodies.

31-May 2021, by Lee Sandwith

Fat adaption

When you first find the keto diet, in all likelihood you have stumbled across a few terms such as “fat adapted”, “keto adapted”, or even “fat burning machine”. But what does it all mean? 

Background

Human metabolism has evolved to be remarkably flexible in how it can use a variety of nutritional inputs.

Culturally speaking, anthropology provides evidence for how humans can thrive across a wide spectrum of dietary options. At one end of the spectrum some cultures thrive through 80% of calories coming from carbohydrates, and others 80% dietary fat.

Most people switching to a ketogenic diet are typically moving from one end of this spectrum to the other. But can we switch from one macronutrient fuel source to another with ease?

This brings us to two interesting and complex keto topics: fat adaption and metabolic flexibility. In this article, I’m going to tackle the former, let’s leave metabolic flexibility to another day.

What is Fat Adaption?

At the most basic level, fat adaption refers to the process of transition where the body switches from relying on using carbohydrates as its main fuel source to ketone bodies.

Most keto heads might associate fat adaption with a few subjective things related to the dissipation of the negative effects of including sugar in the diet, such as:

  • An intense feeling of hunger, or even getting “hangry”
  • The need to eat several times per day
  • Sweet cravings
  • Energy crashes after eating
  • Mental fogginess

Once you comfortably make the transition, you should start to feel some of the benefits that we’ve talked about before: less hunger, consistent energy levels, ability to fast for longer and mental acuity.

These are all what I would consider to be the “subjective” or “behavioural” benefits, but is there something also going on at a metabolic level?

It turns out that there is a substantial amount of quality research which suggests that there is.

One thing that seems to be clear from the research is that having increasing levels of ketone bodies in the blood and fat adaption are not the same thing.

Ketone levels and metabolism

One very clear metabolic difference between high carb and low carb diets is the fuel source.

If you’re following a high carb diet, glucose will be the main fuel source; if you’re following keto, whilst your body will always need glucose, your primary fuel source will switch to ketone bodies.

One thing that seems to be clear from the research is that having increasing levels of ketone bodies in the blood and fat adaption are not the same thing.

This pertains to a number of things which have been eloquently described by Phinney & Volek from the Virta Study in their article “Keto-adaptation”.

It’s a pretty complex piece so let me try to summarise.

Exercise

A number of studies have shown how, although blood ketone levels increase quickly after starting keto, it can several weeks or months for the body to catch up in terms exercise output (Phinney, 1980; Phinney, 1983).

What is typically seen is a dip in performance after starting keto, then an improvement over time where the body catches up to its previous level of performance.

Or, as Phinney & Volek state, “the process of keto-adaptation that allows for normal or increased exercise performance lags well behind the level of ketones in the blood”.

Glycogen

Next on the list is glycogen where the same researchers have shown how, after a period of “keto adaptation”, low-carb athletes demonstrate similar glycogen storage abilities to their higher carb counterparts.

As they put it, “Despite impressive weekly training mileage, their glycogen levels had come all the way back up to those of a matched group of athletes following a high carb diet. This implies that the body’s ability to produce and defend muscle glycogen via gluconeogenesis can become finely tuned, but that this takes much longer than 4-6 weeks to occur” (Volek et.al 2015).

Blood Uric Acid Levels

Another biomarker that suggests the body embarks on a journey of keto adaptation after switching to a ketogenic diet is Uric Acid.

At the onset of nutritional ketosis, many people see a spike in Uric Acid, but over time, this corrects and returns to normal, despite sustained ketone levels in the blood.

Mitochondrial density

Mitochondrial density in muscle, brain, and other tissues might also increase through the process of fat adaption.

This is thought to either be through mitochondrial biogenesis, or decreased mitochondrial damage and autophagy.

Again quoting the authors, “It is understood that reactive oxygen species (ROS) cause structural and functional damage to mitochondria, and that nutritional ketosis decreases mitochondrial ROS production. This could result in a prompt increase in the lifespan of existing mitochondria”.

Conclusion

In conclusion, there is sufficient first-hand, anecdotal experience from people; and high quality, quantitative research which suggests that fat adaption is a real thing.

It seems that how long the process takes is, like most things, very much down to you as an individual and it could take a matter of days, weeks or even months for you to become fully keto adapted.

So, the takeaway is simple: if you’re looking to give keto a shot, you might need to buckle down for a while until you start to realise the full potential of the benefits.

Watch the video

References

  1. Phinney SD, Horton Es, Sims EAH et al. The capacity for moderate exercise in obese subjects after adaptation to a hypocaloric ketogenic diet. J Clin Invest. 1980 66;11-52-1161.13.doi: 10.1172/JCI109945.
  2. Phinney SD, Bistrian BR, Wolfe RR, Blackbiurn GL. The human metabolic response to chronic ketosis without caloric restriction: physical and biochemical adaptation. Metabolism. 1983 32:757-768.14. doi: 10.1016/0026-0495(83)90105-1.
  3. Volek JS, Freidenreich DJ, Saenz C, Kunces LJ, Creighton BC, Bartley JM, Davitt PM, Munoz CX, Anderson JM, Maresh CM, Lee EC, Schuenke MD, Aerni G, Kraemer WJ, Phinney SD. Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism. 2016; 65:100-1015. doi: 10.1016/j.metabol.2015.10.028.

Read Next

Eu omnium laoreet nominati mel, id vis dolore utroque

Lee Sandwith

Leave a comment