Obesity and Reduced Sleep: Will Sleeping Less Make Me Fat?

by | Mar 29, 2010

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.

His website contains reviews of some of the so-called best rated weight loss programs and offers a savings coupon for Medifast, a clinically studied weight loss intervention.

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 [1].

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 [2], this had decreased to less than 8 hours by the late 1960s [3]. 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 [4]. 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 [5], 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 [6].

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.
Matthew Constantin

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22 Responses to “Obesity and Reduced Sleep: Will Sleeping Less Make Me Fat?”

  1. Kate says:

    Sorry if I’m missing something, but it seems like you’re making a leap here from correlation/association to causation. If I’m understanding the summary correctly, reduced sleep is associated with increased weight–people who sleep less weigh more. But you then jump from there to “how does reduced sleep cause weight gain?” I haven’t read the study itself, but from your summary, it doesn’t seem valid to make that jump.

    According to this summary, the study looked only at sleep hours, body weight, and fat distribution. It didn’t study any other aspects of the participants’ lives–for example, WHY they are sleeping less. It seems to me that that information is critical to assessing the true cause of the overweight and the loss of sleep.

    For example, maybe many people who sleep 5 or fewer hours per night do so because they are working long hours/multiple jobs, have kids, etc. People in those situations are also more likely to eat junky food (because it’s cheap and easy), skimp on exercise (because they don’t have time), and not get good medical care (assuming they’re working long hours because they’re poor). In that case, the lifestyle causes both the overweight and the lack of sleep. They aren’t overweight because they don’t sleep enough–they’re overweight and don’t sleep enough because of their circumstances.

    While I agree that getting enough sleep is very important to staying healthy, I don’t see how this study demonstrates causality any more than any of the other studies that have been done.

    • Darya Pino says:

      You’re right Kate. If you read the 1st sentence of the conclusion, you’ll see that Matt agrees with you 🙂

    • Matthew says:

      Your concern about cause and effect is a valid one Kate. Here is some information that will address your skepticism.

      1. The first study was conducted on a relatively “homogeneous” group of people. All 68,183 subjects were married female nurses living in the USA. This lowers the possibility that the weight gain is attributed to differences in lifestyle (work load, income level, multiple jobs, etc)

      2. This was a longitudinal study that lasted for 16 years. This evens out deviations in lifestyle, such as multiple jobs or many kids. Few people work two jobs for 16 years. And kids certainly grow up.

      3. Take a look at the graph at http://www.flickr.com/photos/48839750@N06/4474340956/ which was supposed to be included in the article but was removed for editorial purposes. Notice that the subjects were divided in 5 groups. All participants gained weight during these 16 years. Those who slept less than 5 hours showed the highest weight gain, followed by those who slept 6 or 7 hours.

      But notice this: Those who slept 8, 9 or more hours gained as much weight as those who slept less than 5 hours. If the weight gain of the 5 hour-sleepers is explained on the basis of the “I-am-a-poor-nurse-working-my-butt-off-trying-to-feed-my-kids-and-eat-junk-as-a-result” theory, then how can we explain the weight gain observed in the long-hour sleepers?

      4. Although cause-effect relationship has not yet been established, there is some evidence toward the direction that short sleep sets the stage for obesity, as it affects the levels of hunger hormones.

      5. Anecdotal observation suggests that when we keep ourselves awake for a long time, regardless of the reason —whether partying all day or working 16 hours— we tend to eat more junk, as Sudeep shared. We also tend to drive to a place rather than walk, as Fatima said.


    • Matthew says:

      6. The second study was conducted on 65 years or older community-dwelling women and men. How different can senior’s lifestyles be? Yet, even after adjusting for age, race, level of education, smoking, alcohol and caffeine consumption, medication use, medical history, and **physical activity**, the mean BMI was greater in subjects who slept 5 hours compared to those who slept 7-8 hours.

      To me, the study shows that short sleep itself, and not what causes short sleep, is the primary risk factor for obesity.

  2. Sudeep says:

    I do not know that much about research papers and do not care about them too. But what my lay man mind and common sense tells me about sleep and obesity is the simple fact that when I do keep myself awake for a long time , I tend to eat more junk . Which means that the less I sleep the more obese would I get due to junk food.
    Any thoughts!!

  3. Fatima says:

    I dont know if there is any scientific relation to sleep deprivation and weight gain; but for me, personally, lack of sleep does effect the way I eat and the amount of physical activity I do.

    I feel too tired and fatigued to cook something healthy (chopping vegetables? come on!!) and my body craves sugary and fatty foods. Also I’d drive to a place rather than walk. I’m unorganised with everything from work to meal planning. So in my case this is definitely true!

  4. Ryan says:

    Well once again I am inclined to disagree with such findings.. and this from personal experience.

    I suffered a severe bout of insomnia a few years back which brought about a corresponding increase in mental activity. Whenever I have an increase in mental activity I tend to eat more (Seems to me an increase in mental activity requires more energy). Thus I found myself eating like crazy during that period. In any event I do not put on weight no matter how much I eat or what I eat so I imagine it was just to maintain my weight at that period of my life.

    I will however say that my body seems to react differently to many people but then again that just proves there is no 1 answer fits every scenario.

    If you want some good advice ALWAYS take research like this with a grain of salt and let your body be the real scientist. It’s constantly in communication with you.

    • George G. says:

      You may very well be an “outlayer” in the social graph. Marius Pudzianowkski, a Strongman, has a diet mainly of candy bars, chocolate, coffee, and energy drinks, and regularly does cocaine, but is a large record-holding powerlifter. That type of lifestyle works for him for some reason, but is not recommended for others.

  5. Matthew says:

    Hi Rhian,

    I agree with you. One needs to stay in touch with oneself and pay attention to its body’s signals.

  6. Kevin says:

    Less sleeping hours = a higher risk of me eating ice cream.. like last night.. around midnight.. oops.

    • Darya Pino says:

      Maybe it’s time I start giving away WWDE (what would Darya eat?) plastic bracelets? You could wear it on your ice cream grabbing arm as a reminder.

  7. Katie says:

    I’m not surprised by the findings in the study. From my own personal experience, it seems easiest for me to lose weight or maintain a healthy weight if I can eat well and exercise (probably true for most). I realized one summer that I was a lot more successful if I could also sleep more. Now that I’m older, I consider sleep as important as eating well and exercising.

  8. Interesting. What I find is that if I have a very poor night’s sleep that my hunger/satiety filter is just flat the next day…like the batteries have died. I can’t tell if I’m hungry or full and I tend to just eat and eat. Not good. So 7 hours is quite necessary for me, my sanity and my waistline.

  9. Jan says:

    What a coincidence that this is your latest post and I cannot sleep right now! I was on Timothy Ferriss’ website and OMG Kevin Rose plugged your site! So awesome you know those guys! I thought you were just a normal person like me who was only a fan of Timothy Ferriss’ book! Good stuff! Nice to know your stuff is getting recognized more and more. 🙂

  10. Jill says:

    I know this is just anecdotal but I recently experienced the reverse of lack of sleep = weight gain. For months I have been trying to take off the weight I gained during my pregnancy. Even after I stopped nursing, I still couldn’t lose it. Then about a month ago I noticed that my clothes were looser and I stepped on a scale- I had lost about 11 pounds. Nothing I could think of had changed. Not my diet or exercise, both of which I’ve been logging on a daily basis for sometime now so any changes would have been recorded.

    Around the same time I was telling someone that my son was finally sleeping through the night, every night, for about a month. Which meant for the first time since before he was born, so was I. It made me wonder if my increased sleep was helping me lose weight.

    I’m just a sample of one, and there could be a confounding variable I haven’t thought of yet, but common sense tells me that my body overall is functioning better with more sleep. And the weight loss has motivated me to make sure I’m getting lots of rest.

  11. Andrea says:

    Great article and although I have read my fair share about sleep deprivation and weight gain there was still quite a bit to learn from that article. I to my mind it does by no means state that reduced sleep is the single cause of weight gain yet it does quite rightly suggest that people who gain weight might want to assess their sleep pattern.

    Most interesting comment came from Jill and makes me wonder whether it would be worth studying if people could lose weight simply by increasing their sleep hours to about 7-8h per night, as too long sleep seems to effect the human metabolism negatively too.

    Thanks for this great article!

  12. Valerie says:

    Thank you so much for this information. I have always struggled to maintain a healthy weight and I have never been a good sleeper.
    When I get overtired, I want to eat more and seem to lose the control to regulate what I eat.
    So what is the answer for those who have the time to get more sleep but still wake up several times in the night and then are fully awake after 6 or 7 hours?

    • Darya Pino says:

      That’s a great questions, Valerie. I have that problem, and have just learned to deal with it. I regulate my weight with my food choices and exercise.

    • Jill says:

      Valerie- Just a thought… Have you had a sleep study? A few years ago I mentioned to my doctor that I was waking up several times a night (I blamed the neighbors) and he sent me for a sleep study. Turns out I have very mild sleep apnea, but enough to rouse me. I wasn’t overweight and the sleep doc explained that you don’t necessarily have to be overweight to get sleep apnea, in fact he believes that people become overweight because of sleep apnea (and other sleep issues). Kind of goes along with this entire thread. Good luck!

    • George G. says:

      Simple things like sleeping in total darkness and taking a little magnesium before bed can improve your ability to stay asleep longer.

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