By Dr. Stephen Phinney and the Virta Team
This term is often used synonymously with keto-adaptation, and commonly used to describe low-carb adapted athletes. If you are fat-adapted, it implies you have restricted carbs enough to induce an increase in fat burning. Fat-adapted athletes, and sedentary folks, can derive up to twice as much of their energy needs from fat, while decreasing their dependency on carbs (Volek, 2011; Volek, 2016). Whereas fat adaptation can occur to different degrees and across a spectrum dependent on the degree of carb restriction, keto-adaptation represents a more comprehensive reshaping of many physiologic systems. Keto-adaptation only happens when carbs are restricted to a point that induces sustained nutritional ketosis. The nuances here are subtle, but meaningful. For example, moderately restricting carbs (e.g., adaptation to a Paleo diet) may induce some degree of fat-adaptation and perceived benefits, but falls short of maximizing fat oxidation and producing positive health outcomes specifically linked to nutritional ketosis. A keto-adapted person is by definition fully fat-adapted, but a fat-adapted person may not be keto-adapted.
Read more in our deep dive on ketone basics here: https://blog.virtahealth.com/ketone-ketosis-basics/
Volek JS, Phinney SD. The Art and Science of Low Carbohydrate Living. Beyond Obesity, Miami FL, 2011.
Volek JS, Freidenreich DJ, Saenz C, et al. Metabolism. 2016 Mar;65(3):100-10. doi: 10.1016/j.metabol.2015.10.028. Epub 2015 Nov 2.