Alternate day fasting—a new approach to energy balance and life extension?

Nutrition Research Newsletter, Feb, 2005

Prolonged dietary restriction (DR) is the only proven way to increase the life span in study animals. The mechanism or mechanisms by which DR increases life span are unclear, but they may include reduced metabolic rate, reduced oxidative damage, altered neuroendocrine signaling, and improved insulin sensitivity. A pilot study testing the feasibility and effects of long-term DR on biomarkers of longevity in nonobese humans is being performed. Alternate-day fasting may be an alternative to prolonged DR as a method of increasing maximal life span in humans. However, the feasibility and efficacy of alternate-day fasting has yet to be investigated.

A team of researchers recently investigated the feasibility of alternate-day fasting in nonobese subjects. Additionally, the effects of alternate-day fasting on body weight, RMR, fat oxidation, and biomarkers of longevity were investigated. The subjects included healthy, nonobese men (n = 8) and women (n = 8) between the aged of 23 and 53 years. The subjects were required to attend the clinical research center on two consecutive days at baseline and on 2 consecutive days after the three weeks of alternate-day fasting, following a feast day. At each visit, the subjects were weighed and blood pressure was measured. On days 2 and 21, body composition was measured using dual-energy X-ray absorptiometry. At baseline and on days 1, 7, 15, and 21 (fasting days), the subjects completed visual analogue scales at various times during the day to assess their feelings of hunger, fullness, desire to eat, satisfaction, and prospective food consumption. At baseline the subjects completed the Eating Inventory questionnaire, which assessed dietary restraint, disinhibition, and hunger. They also completed The Eating Behaviors Questionnaire.

On each fasting day, the subjects were allowed to consume energy-free beverages, tea, coffee, and sugar-free gum, and were instructed to keep their water intake high. On each feasting day, the subjects were instructed to eat whatever they wished and were informed that double their usual food intake would be required to maintain their usual body weight. Biochemical analyses included glucose, free fatty acids, B-Hydroxybutyrate, insulin and ghrelin.

Subjects lost 2.5 [ or -] 0.5% of their initial body weight (P< 0.0001) and 4 [ or -] 1% of their initial fat mass (P < 0.001) Hunger increased on the first day of fasting and remained elevated (P < 0.001). Resting metabolic rate and the respiratory quotient did not change significantly from baseline to day 21, but respiratory quotient decreased on day 22 (P < 0.001), which resulted in an average daily increase in fat oxidation of > 15 grams. Glucose and ghrelin did not change significantly from baseline with alternate-day fasting, whereas fasting insulin decreased 57 [ or -] 4% (P < 0.001).

Alternate-day fasting appears feasible in nonobese subjects. However, because hunger on fasting days did not decrease, it is likely that individuals may not be able to continue this diet for extended periods of time. Researchers suggest that adding one small meal on a fasting day may make this approach to dietary restriction more acceptable.

L. Heilbronn, S. Smith, C. Martin, et al. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. Am J Clin Nutr;81:69-73 (January, 2005). [Correspondence: E Ravussin, Pennington Biomedical Research Center, 6400 Perkins Road, Baton Rouge, LA, 70808. E-mail: ravusse@pbrc.edu].