muscleprofketoadaptedBeing “Keto-Adapted” or “Keto-Adaptation” is a term that was coined by Steve Phinney back in 1980.


Keto-adaptation is the process of shifting your metabolism from relying mostly on glucose for fuel, to relying mostly on fat-based sources of fuel. Not only does fat oxidation (the breaking down of stored body fat) itself increase, but your body starts producing  ketones so they can be used as your body’s primary fuel source.

Ketones are derived from partially metabolized fat, and they can be used in many of the same tissues of the body as glucose can, including much of the brain. The benefits of using fat and ketones rather than glucose for fuel are many, and are the main subject of this site. However, it takes time for the metabolism to adjust to producing and using ketones at a significant rate. Even though changes are evident within days of carbohydrate restriction, improvements continue for weeks.

Even though ketone metabolism has been well studied it is not well understood by many physicians, dietitians or nutritionists.

In his study entitled “Metabolic Effects of the Very-Low-Carbohydrate Diets: Misunderstood “Villains” of Human Metabolism” [3], Anssi H Manninen sets the record straight on the villianization of ketones and low-carb diets.

He states “According to the American Heart Association (AHA) Nutrition Committee, “Some popular high-protein/low-carbohydrate diets limit carbohydrates to 10 to 20 g/d, which is one fifth of the minimum 100 g/day that is necessary to prevent loss of lean muscle tissue [1].”

Clearly, this is an incorrect statement since catabolism of lean body mass is reduced by ketone bodies (possibly through suppression of the activity of the branched-chain 2-oxo acid dehydrogenase), which and probably explains the preservation of lean tissue observed during very-low-carbohydrate diets.

Unfortunately, the leading exercise physiology textbook also claims a “low-carbohydrate diet sets the stage for a significant loss of lean tissue as the body recruits amino acids from muscle to maintain blood glucose via gluconeogenesis [2].”

There is so much misinformation and misunderstanding when it comes to the importance of carbohydrates and their role as being the preferred fuel for physical performance.

In our next article we will take a look at some keto-adaptation experiments in endurance athletes.

About Dr. Stephen Phinney

Dr. STEPHEN PHINNEY a physician scientist who has spent 35 years studying diet, exercise, fatty acids, and inflammation.  He has held academic positions at the Universities of Vermont, Minnesota, and California at Davis; and leadership positions at Monsanto, Galileo Laboratories, and Efficas.  He received his MD from Stanford University, PhD in Nutritional Biochemistry from MIT, and did post-doctoral research at Harvard.

He has designed, completed, and published data from more than 20 clinical protocols involving foods, diets, exercise, oxidative stress, and inflammation.  His recent work in the private sector has resulted in several issued and pending patents.  He has authored more than 70 peer-reviewed papers and book chapters on a wide variety of topics, including the effects of diets and specific nutrients on inflammation, the interaction between diet and exercise and their effects on obesity, body composition, physical performance, and cellular membrane structure.

Dr. Phinney’s clinical experience includes 20 years of inpatient and outpatient clinical nutrition, including directing multidisciplinary weight management programs in 3 locations.  As an internationally recognized expert in obesity, carbohydrate-restricted diets, diet and performance, and essential fatty acid metabolism, he has given hundreds of presentations to industry, health care professional, and lay audiences.

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  1. St Jeor ST, Howard BV, Prewitt E: Dietary protein and weight reduction: A statement for health care professionals from the Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association. Circulation. 2001, 104: 1869-1874. 10.1161/hc4001.096152.
  2. McArdle WD, Katch FI, Katch VL: Exercise Physiology: Energy, Nutrition and Human Performance. 2001, Philadelphia: Lippincott Williams & Wilkins
  3. Metabolic Effects of the Very-Low-Carbohydrate Diets: Misunderstood “Villains” of Human Metabolism, Anssi H ManninenEmail, Journal of the International Society of Sports Nutrition20041:7 DOI: 10.1186/1550-2783-1-2-7

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