Very low carb diets could be incompatible with exercise

dr. M Zanetti

While very low carbohydrate (ketogenic) diets are popular with those trying to lose weight, there are concerns that such diets may not support the desire for exercise. This hypothesis was investigated by a US research team at Arizona State University.

Untrained overweight adults were randomly assigned to a ketogenic diet or a control diet, which was higher in carbohydrates. Both diets were designed to promote weight loss and were consumed for 2 weeks. The macronutrient content of the diets was 5% energy from carbohydrate, 65% from fat and 30% from protein in the ketogenic diet. In the control diet, the respective figures were 40%, 30%, and 30% of energy. Exercise testing was carried out at baseline and at the end of the study.

Average weight loss was similar over the 2-week period for both groups. As expected, subjects following the ketogenic diet demonstrated a large build up of blood ketones, indicating that their bodies were burning fat. Having a high blood ketone level was significantly associated with greater perceived effort during exercise and an increased feeling of fatigue.

The authors concluded that very low carbohydrate ‘ketogenic’ diets could reduce the desire to exercise and, thus, be counter productive for weight management.

For more information, see 
White AM et al (2008). 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. Journal of the American Dietetic Association, Vol 107, pages 1792-96.