Blood ketones are directly related to fatigue and perceived effort during exercise in overweight adults adhering to low-carbohydrate diets for weight loss: a pilot study

J Am Diet Assoc. 2007 Oct;107(10):1792-6. doi: 10.1016/j.jada.2007.07.009.


Ketogenic diets have been associated with reductions in free-living physical activity, a response that can be counterproductive in individuals trying to lose weight. To explore whether popular low-carbohydrate diets might impact the desire to exercise by raising blood ketone concentrations, fatigue and perceived effort during exercise were compared in untrained, overweight adults adhering to a ketogenic low-carbohydrate diet or to a control diet low in carbohydrate, but not ketogenic (5%, 65%, and 30% or 40%, 30%, and 30% of energy from carbohydrate, fat, and protein, respectively). In this prospective, randomized, 2-week pilot study, all meals and snacks were provided to subjects, and energy intake was strictly controlled to provide approximately 70% of that needed for weight maintenance. At baseline and at the end of week 2, exercise testing was conducted in fasting participants. Weight loss and the reductions in fat mass did not differ by group during the trial. At week 2, blood beta-hydroxybutyrate concentrations were 3.6-fold greater for the ketogenic vs nonketogenic group (P=0.018) and correlated significantly with perceived exercise effort (r2=0.22, P=0.049). Blood beta-hydroxybutyrate was also significantly correlated to feelings of "fatigue" (r=0.458, P=0.049) and to "total mood disturbance" (r=0.551, P=0.015) while exercising. These pilot data indicate that ketogenic, low-carbohydrate diets enhance fatigability and can reduce the desire to exercise in free-living individuals.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Diet, Carbohydrate-Restricted* / adverse effects
  • Dietary Carbohydrates / administration & dosage
  • Dietary Carbohydrates / metabolism
  • Dietary Fats / administration & dosage
  • Dietary Fats / metabolism
  • Dietary Proteins / administration & dosage
  • Dietary Proteins / metabolism
  • Energy Metabolism
  • Exercise / physiology*
  • Exercise / psychology
  • Fatigue / blood*
  • Female
  • Humans
  • Ketones / blood*
  • Male
  • Middle Aged
  • Obesity / blood
  • Obesity / diet therapy*
  • Overweight
  • Pilot Projects
  • Prospective Studies
  • Weight Loss


  • Dietary Carbohydrates
  • Dietary Fats
  • Dietary Proteins
  • Ketones