People who are on a low-calorie diet will lose the same amount of weight whether they sleep an average of 8.5 hours or 5.5 hours each night. However, those on 8.5 hours will lose much more fat, while those on 5.5 hours lose mainly muscle, instead of fat, according to an article published in the peer-reviewed journal Annals of Internal Medicine. The researchers, from the University of Chicago stress that adequate sleep is a key contributor to managing body weight.

The investigators advise those planning to start a weight-loss program to try to make sure they know they are going to get enough sleep each night.

Ten overweight males and females lived in a sleep research center for two separate periods, lasting two weeks each. During each period they were on identical low calorie diets. However, during the first 2 week period they had 8.5 hours sleep each night, while in the second period they slept just 5.5 hours each night.

Although sleep duration was found not to affect the total amount of weight loss - they all lost an average of nearly 7 pounds - the dieters lost mainly muscle rather than fat during their sleep-deprived two-week session.

The researchers found that:
  • While on 8.5 hours sleep each night over 50% of the participants' weight loss consisted of fat
  • While on 5.5 hours sleep each night, approximately 25% of the participants' weight loss consisted of fat - in other words, they lost 55% less fat than when they were sleeping 8.5 hours
Dr. Plamen Penev, assistant professor of medicine, the University of Chicago, a senior researcher, said:

So they lost the same amount of weight, but the composition was different.

Weight-loss dieting usually involves a certain amount of lean tissue (muscle) loss. The dieter should try to lose as little lean tissue as possible. This can be overcome by physical activity (exercise). However, it is clear that not getting enough sleep can undermine any attempts a dieter may make to limit lean tissue loss.

The investigators stressed that longer and larger studies are needed to confirm their findings. The current study was a very small and short-lasting one.

The authors concluded:

The amount of human sleep contributes to the maintenance of fat-free body mass at times of decreased energy intake. Lack of sufficient sleep may compromise the efficacy of typical dietary interventions for weight loss and related metabolic risk reduction.

How much sleep do I need? What is sleep?

When we are asleep, our senses and motor activity are relatively suspended, there is total or partial unconsciousness - our voluntary muscles are inactive. Sleep is the body's rest cycle.

During sleep the body is producing new bone, muscular and nervous tissue, it is a period when growth and repairs occur - it is a heightened anabolic state.

Virtually all animals sleep, including mammals (which we are), birds, most reptiles, fish and amphibians.

Sleep is triggered by a complex group of hormones which respond to cues within our body, as well as in the environment. About three-quarters of our sleep time is without dreams, a period called NREM (non-rapid eye movement). Dreams occur mainly during REM (rapid eye movement).

How much sleep an individual needs depends on several factors, including age, type of routine, general state of health and individual circadian rhythms (body clock). The figures below are general approximations, depending on age:
  • Newborn baby - up to 18 hours
  • 1 to 12 months of age - 14 to 18 hours
  • 1 to 3 years of age - 12 to 15 hours
  • 3 to 5 years of age - 11 to 13 hours
  • 5 to 12 years of age - 9 to 11 hours
  • Teenagers - 9 to 10 hours
  • Adults - 7 to 8+ hours
  • Women during pregnancy - at least 8 hours
The above figures should be seen, at best, as a very rough guide. People's needs can vary significantly.

Click here to read about sleep in more detail.

"Insufficient Sleep Undermines Dietary Efforts to Reduce Adiposity"
Arlet V. Nedeltcheva, MD, Jennifer M. Kilkus, MS, Jacqueline Imperial, RN, Dale A. Schoeller, PhD, and Plamen D. Penev, MD, PhD
Annals of Internal Medicine October 5, 2010 vol. 153 no. 7 435-441

Written by Christian Nordqvist