Many studies have been published associating lack of sleep with increased body weight, but I have never read through the literature myself to explore the connection.
This week fellow scientist Matthew Constantin of Best Weight Loss Triumph gives us a thorough review of the science of sleep and weight gain.
Matthew Constantin, PhD, is a biologist and postdoctoral research scientist at Saint Louis University. Twice awarded research grants from the American Heart Association for his studies on cardiovascular disease, Matthew also has a keen interest in the related field of obesity treatment and enjoys explaining the latest scientific research on weight loss in a way that is easy for everyone to understand.
Obesity and Reduced Sleep: Will Sleeping Less Make Me Fat?
By Matthew Constantin, PhD
We have long known that too little sleep causes fatigue and a slowing of neurocognitive functions, resulting in a variety of symptoms like slowed reaction time and difficulty concentrating. Recent research, however, has discovered a new result of reduced sleep: metabolic effects that include an increased risk of obesity .
Western society has seen a rapid rise in overweight and obesity in recent decades. Accompanying this widespread weight gain has been a significant and rapid decrease in the amount of time the average person spends sleeping.
While young adults were sleeping close to 9 hours each night at the beginning of the 20th century , this had decreased to less than 8 hours by the late 1960s . The trend is continuing into the 21st century. As of 2005, 16% of American adults were getting less than 6 hours of sleep at night, up from 12% in 1998.
Sleep and Obesity: A Subjective Study
Science has linked self-reported sleep habits and obesity for a number of years, but the precise relationship between the two has been difficult to establish. Because obesity is a risk factor for a number of diseases that can negatively impact sleep, such as sleep apnea, asthma, depression, and arthritis, it is hard to know whether reduced sleep leads to obesity or obesity leads to reduced sleep.
To shed some light on this question, data collected from 1986 to 2002 in the Nurses’ Health Study (NHS) was analyzed . Women in this study were asked to report their sleep habits and body weight every two years.
The results of the study suggest that women who self-report receiving less sleep are more likely to gain weight and are at an increased risk for obesity in middle-age. In 1986, when the first round of data was collected, it was found that women who reported sleeping 7 hours in a 24 hour period weighed 2.6 kg less than those who slept 5 or fewer hours, and 1.3 kg less than those who slept 6 hours.
This pattern continued over the following 16 years, with women who reported getting 5 or fewer hours of sleep weighing the most every time weight data was collected and those getting 7-8 hours of sleep weighing the least. In 2002, those in the 6-hour group had gained 7.2kg (15.8lb) and those in the 5-hour or less group gained 9kg (19.8lb), while those in the 7-hour group had gained only 4.8 (10.6lb) kg.
Other prospective studies have found similar results among both adults and children, but there are a couple of caveats. Because the information in the studies is self-reported, it is subject to inaccurate estimates by the reports. Many people overestimate sleep time when self-reporting. It is also unknown whether shorter sleepers are heavier because of an increase in fat or an increase in lean muscle—a distinction which makes a significant difference for health repercussions.
Sleep and Obesity: An Objective Study
In response to the limitations of subjective studies on sleep and obesity, two groups of adults aged 65+ (one of men and one of women) took part in an objective study that also looked at sleep duration and weight. Rather than relying on self-reported data, participants’ sleep patterns were assessed through the use of wrist actigraphy, which determines if a person is asleep or awake by measuring wrist movement.
This objective measurement of sleep duration confirmed the results of the subjective study, finding that reduced sleep was associated with an increased Body Mass Index (BMI) among both men and women. When compared with those getting 7-8 hours of sleep per night, average BMI of those who slept less than 5 hours was higher by 2.5 units in men and by 1.8 units in women. Moreover, men getting 5 or fewer hours of sleep were 3.7 times more likely to be obese, while women were 2.3 time more likely.
Increased weight doesn’t necessarily mean an increase in fat and its related health problems—more muscle also means more weight, but is generally associated with improved health. The objective study looked at this question and found that the increase in weight associated with reduced sleep was a result of increased fat rather than muscle. Overall percent body fat in those sleeping less than 5 hours was 1.7% greater than those getting 7-8 hours, and percent body fat in the trunk 1.9% greater.
Why Could Reduced Sleep Make You Fat?
Research has clearly shown that reduced sleep is associated with greater weight, but why does reduced sleep make a person fat?
One strong hypothesis is that less sleep leads to increased or altered food intake. Animals studies have found that sleep deprivation leads to elevated levels of hunger , with particular increases for high-fat and high-carbohydrate foods. This increased hunger with sleep deprivation may be a result of the corresponding change in hormones that regulate hunger, with gherlin levels found to increase and leptin levels to decrease.
Alternatively, rather than a change in feelings of hunger, increased food intake could be the result of increased eating even in the absence of hunger. Reduced impulse control and trouble delaying gratification are known consequences of sleep deprivation.
It’s also possible that simply being awake more often will lead to increased eating when food is readily available, especially if time awake is spent in sedentary activities that encourage snacking.
As S.R. Patel mentions in his 2009 review paper titled “Reduced sleep as an obesity risk factor”, there are several other possibilities that have been proposed. One is that the feelings of fatigue that are associated with sleep deprivation may result in a disinclination to exercise. Another is that reduced sleep results in a reduction in involuntary activities such as fidgeting, which are known to have effects on weight regulation .
Finally, acute sleep deprivation has been found to result in a drop in core body temperature, meaning your body needs to spend less energy in order to maintain thermoregulation with the surrounding air. This change in thermogenesis (the process of heat production) may encourage the storing of fat, although a recent study found no effect of sleep deprivation on resting metabolic rate.
Current evidence clearly shows that short sleep is associated with obesity, but a causal relationship remains unclear. Does a reduction in sleep lead to weight gain, or is there some other reason for the association? We don’t yet know for sure. But as modern society sets aside less and less time for sleep and becomes increasingly prone to obesity, it is a possibility that must be considered.
With so few effective ways to prevent and treat obesity, wouldn’t it be wonderful if simply sleeping a bit more could keep us both thinner and healthier?
1. Patel, S.R. Short sleep and obesity. International Association for the Study of Obesity. Obesity Reviews 10 (Suppl. 2), 61–68.
2. Terman L, Hocking A. The sleep of school children, its distribution according to age, and its relationship to physical and mental efﬁciency. J Educ Psychol 1913; 4: 269–282.
3. Tune GS. Sleep and wakefulness in normal human adults. Br Med J 1968; 2: 269–271.
4. Patel SR, Malhotra A, White DP, Gottlieb DJ, Hu FB. Association between reduced sleep and weight gain in women. Am J Epidemiol 2006; 164: 947–954.
5. Spiegel K, Tasali E, Penev P, Van Cauter E. Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Ann Intern Med 2004; 141: 846–850.
6. Levine JA, Eberhardt NL, Jensen MD. Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science 1999; 283: 212–214.