Your fat percentage is too high; you reduce your calorie intake and you hope and pray that you retain lean body mass and lose as much fat as possible. According to researchers at the University of Chicago, the success of this strategy depends on the number of hours you sleep each day.
Sleep, calories & body composition
The link between obesity and sleep is nothing new. Epidemiological studies have shown that people who sleep little put on weight twice as fast as people who get eight hours’ sleep a night, [Am J Epidemiol. 2006 Nov 15;164(10):947-54.] and small studies have shown that for every hour of sleep you get in a period of 24 hours your fat percentage is three percent lower.
Lack of sleep stimulates appetite. Not getting enough shuteye lowers the production of appetite suppressant hormones such as leptin, and it stimulates the production of appetite boosting hormones such as ghrelin.
Don’t underestimate the effect of lack of sleep on energy intake. In 2010 French researchers published the results of an experiment in which they let students sleep in a laboratory for about four hours a night. [Am J Clin Nutr. 2010 Jun; 91(6): 1550-9.] As a result of the lack of sleep the students spontaneously ate 560 kcal more than they would have eaten after eight hours of sleep a night. That would mean that in less than two weeks the students could have gained a kilogram of fat.
The Chicago research shows that it’s not just an unhealthily large appetite that affects dieters with a sleep deficiency. The researchers did a small experiment with ten slightly overweight adults. The subjects followed a diet twice in a laboratory where the researchers were able to control the amount the subjects ate.
During their two-week stay in the lab the subjects were given ninety percent of the kilocalories they would burn if they got no exercise. On one occasion the subjects were allowed to sleep for 8.5 hours a night [open circles] and on the other occasion they were allowed to sleep for 5.5 hours [black circles].
At the end of each of the two-week periods the subjects had lost the same amount of weight, the researchers discovered. But there were statistically significant differences in the effect on the subjects’ body composition. When the subjects were only allowed to sleep for 5.5 hours, they lost 55 percent less fat mass and 60 percent more lean body mass.
The combination of a calorie-reduced diet and too little sleep [TIB-5.5h] boosts levels of the appetite hormone ghrelin and lowers the level of the pep hormone nor-epinephrine.
The latter effect may explain the figure above. The respiratory quotient [RQ] is higher in the subjects when they have too little sleep [black circles] than when they get enough sleep [open circles]. That means that a shortage of sleep reduces the amount of fat that the body burns.
“These results highlight the importance of human sleep for the maintenance of fat-free body mass during periods of reduced energy intake and raise the possibility that insufficient sleep may compromise multiple factors that contribute to the efficacy of and adherence to dietary energy-restriction strategies for metabolic risk reduction”, write the researchers.
Insufficient sleep undermines dietary efforts to reduce adiposity.
Sleep loss can modify energy intake and expenditure.
To determine whether sleep restriction attenuates the effect of a reduced-calorie diet on excess adiposity.
Randomized, 2-period, 2-condition crossover study.
University clinical research center and sleep laboratory.
10 overweight nonsmoking adults (3 women and 7 men) with a mean age of 41 years (SD, 5) and a mean body mass index of 27.4 kg/m² (SD, 2.0).
14 days of moderate caloric restriction with 8.5 or 5.5 hours of nighttime sleep opportunity.
The primary measure was loss of fat and fat-free body mass. Secondary measures were changes in substrate utilization, energy expenditure, hunger, and 24-hour metabolic hormone concentrations.
Sleep curtailment decreased the proportion of weight lost as fat by 55% (1.4 vs. 0.6 kg with 8.5 vs. 5.5 hours of sleep opportunity, respectively; P = 0.043) and increased the loss of fat-free body mass by 60% (1.5 vs. 2.4 kg; P = 0.002). This was accompanied by markers of enhanced neuroendocrine adaptation to caloric restriction, increased hunger, and a shift in relative substrate utilization toward oxidation of less fat.
The nature of the study limited its duration and sample size.
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.
PRIMARY FUNDING SOURCE:
National Institutes of Health.
PMID: 20921542 [PubMed – indexed for MEDLINE] PMCID: PMC2951287