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Chubby Owls and Skinny Larks?

One of the recurring topics at the Obesity Summit was the importance of sleep in terms of its effects on ingestive behaviour, metabolism and other important parameters.

Now a study by Kelly Baron and colleagues from Northwestern University, Chicago, published in OBESITY, adds an additional dimension to this discussion, i.e. the importance of sleep timing.

As regular readers may recall, I have previously posted the results of animal studies demonstrating the impact of timing of feeding in energy homeostasis – feeding mice during the day (their night) leads to more weight gain than feeding them the same amount of calories during the night (their day).

In their study, Baron and colleagues now evaluated the role of sleep timing in dietary patterns and BMI in 52 (25 females) volunteers who completed 7 days of wrist actigraphy and food logs.

Participants were classified as having normal sleep times if midpoint of sleep was between 1:00 am to 5:29 am, and participants were classified as having late sleep times if midpoint of sleep was 5:30 am or later, which is past the 50th percentile of sleep times in the population (4:00 am)

Late sleepers also consumed more calories at dinner and after 8:00 PM, had higher fast food, full-calorie soda and lower fruit and vegetable consumption.

Not surprisingly, therefore, higher BMI was associated with shorter sleep duration, later sleep timing, caloric consumption after 8:00 PM, and fast food meals.

In addition, calories consumed after 8:00 PM predicted BMI after controlling for sleep timing and duration, suggesting that eating after 8:00 PM may increase the risk of obesity, independent of sleep timing and duration.

If these associations are indeed causally related (which will need to be demonstrated in intervention trials), two important clinical recommendations could emerge:

Get at least half your night’s sleep before 5.30 am and get your day’s supply of calories before 8.00 pm.

Wonder if anyone has experienced changes in their eating behaviour and/or weight with changes in sleep timing or not eating after 8.00 pm.

As for me, I probably just need to figure out which time zone actually counts for me – after all, it is always before 8.00 pm somewhere.

Edmonton, Alberta

Baron KG, Reid KJ, Kern AS, & Zee PC (2011). Role of Sleep Timing in Caloric Intake and BMI. Obesity (Silver Spring, Md.) PMID: 21527892


  1. What strikes me more in this description of those who are fatter and get to sleep late is that their general profile corresponds to what we would probably call a “less healthy lifestyle”: higher fast food, full-calorie soda and lower fruit and vegetable consumption.

    Who are these people? Do they work the night shift, what socio-economic bracket do they belong to? Are they single parents with little money or time to prepare more nutritious foods?

    Methinks there’s much more to it than simply “bad sleep hygiene leads to overweight.”

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  2. As always very interesting. You’ve posted elsewhere on stress, trauma history, addiction, and weight gain issues. My anecdotal experience is that a) all three are frequently found alongside sleep disturbances and b) sleep patterns are extremely hard and slow to change. To me this says that as always, identifying possible sources for the sleep problems alongside other factors which contribute to weight gain is important, and for physicians to appreciate the complexity and pacing of change for a patient in any/all of these areas is crucial. When making the recommendation as you have to get 1/2 your night’s sleep before 5:30 there is a cohort of people for whom the amount of focus and work (and probably frustration!) it will take to get there, is significant – however worthwhile the outcome is (though knowing how helpful you expect it to be may support the patient’s motivation to stay with it).

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  3. “Insomnia”, an remarkable book by Gayle Greene, discusses the relationship between troublesome sleep issues and problem eating patterns in way that does not hold individuals responsible for magically curing themselves of either dis-eases. As noted by commenters NewMe and Linda, above, there is far more complexity going on than can be corrected by training oneself to eat before 8 pm or by improving one’s sleep hygiene. Trauma (which includes various forms of socially-constructed oppression and inequality) and chronic stress (again, related too frequently to socially constructed conditions of economic insecurity and lack of social supports) result in far more illnesses and diseases than are caused by obesity. But obesity appears (wrongly) to be a secure target at which to aim, and to control or manage, while trauma and chronic stress continue to escape notice as significant determinants of health.

    Thanks, Dr. Sharma, for once again suggesting there is more complexity underlying the discourse on health issues.

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  4. I agree with NewMe. There’s really an elephant in the room when it comes to this study: people with late sleeping patterns as they’re defined here couldn’t possibly have a job with standard hours. So who are we talking about? Retirees? People on public assistance? Students?

    Perhaps most importantly, people who regularly sleep in probably don’t have much structure to their work days and (I would imagine) are less likely to eat three regular, communal meals.

    This sounds like a study that does a poor job of supporting its hypothesis. It sounds like pure guess work; a classic example of correlation not necessarily equalling causation.

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  5. I was diagnosed with narcolepsy + some kind of circadian rhythm dysfunction several years ago, and am finally, with the help of drugs, able to more or less regulate my sleep times. I also radically altered my meal timing, partly on purpose to help reinforce the sleep schedule, but mostly as a consequence of going to bed so early now. In the past, I rarely even started to prepare dinner before 8:00 pm. Now if I haven’t eaten by seven or eight, I generally skip dinner because it is too uncomfortable to go to bed so soon after eating. And now I need to have food with the medications I take in the morning, so breakfast is definitely a new habit, and one I like better than I thought I would. I’ve never consumed much fast food or sweetened beverages, and I rarely have “snack” type foods, so the types of foods I eat have not changed, and the quantities are approximately similar. I dislike large meals at any time of day (they make me sleepy!), so I do generally have small meals throughout the day. Because so much of my time is now devoted to sleeping and preparing for sleep, I have a lot less time available to do what needs doing, and I exercise somewhat less than before.

    So despite achieving the new improved sleep patterns of a lark (and to say nothing of heavy stimulant use), my weight is about the same as ever (which is to say high). I do make an effort not to gain any more weight, but my last few actual weight loss attempts have severely strained my efforts to maintain my sleep schedule, and have been generally not successful.

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  6. Also, in answer to who are these owls with their wacky nonstandard sleep patterns? Yes, some are shiftworkers, students, and waitresses, but also nurses, and air traffic controllers, and doctors, and telephone operators, and musicians, and writers, and web designers, and I’ve even heard of a few lucky ones who find a way to telecommute to another time zone! I am sure that there are also some who are public assistance dependent single parents, or fast food gobbling retirees or whatever, but it’s quite possible to have a respectable career and decent income outside the world of “standard hours.” Just as it’s entirely possible to work standard hours for minimal pay in hideous abusive (and obesigenic) conditions.

    Am I a little touchy about this? I guess so, LOL. I’m currently devoting a lot of energy and resources to maintaining “standard hours,” mostly for a job. But as pointed out multiple times above, I’m not sure we have enough info from this study to establish cause/effect, etc.

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  7. Nora, interesting observations. What really struck me was your observation that there are people who telecommute to different time zones. Made me go Hmmmm.

    One question in the area of obesity studies that interests me is, simply, what is causing the movement of the bell curve that plots our average weight? (I think the idea that we are moving less is cultural mythology, and that we are eating more is also suspect — we are eating differently, more processed foods, but more? My dad in the 60s would not have recognized a steak the size of a deck of cards.) Now, I think it’s some obesogenic toxin — livestock growth hormones, remnants of birth control effluent in our drinking water, TBHQ preservative, increased inflamation from transfats, pesticides or some such, but I wouldn’t be surprised to learn that it’s sleep cycle related. That is something that has also morphed in the past four decades corresponding to our rise in average weight.

    Your thought on telecommuters makes me think that a really interesting study would follow people from India who have joined the ranks of technical support for North American businesses. It’s a huge pool of people to study. What’s happened/continues to happen to their weight? Is there a grad student in the house?

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  8. Dear Doctor: I find in my case because I am on a disablitity pension [(aish) assured income for the severally handicapped–not physically in my case] what I have by way of a bedtime snack the night before often dictates whether or not I wish to eat first thing in the morning. if my hands hurt to much to peal potatotoes or carrots the is always rice or pasta to call on with frozen or canned vegetables to round out the meal. I do find if I have a late supper or large bedtime snack it is very easy for me not to eat again until lunch time–just not hungery. I also find that in the summer when there are many hours of daylight I get sleep deprived and my depression says ‘hello I’m back” not plesant, but I do not feel like over eating then.

    I think that it is the amount of sunlight that causes too much seritonin to be produced in me that causes som of the summertime relapse for me–afterall too much of a chemical can be as bad as to little. There are two other people with summertime seasonal depression at the clubhouse for mental health consumers where I hang out regularly. Feeling tired is a common reason for people who eat too much to want to eat more especially for those with exsisting weight issues. I know in the summer I use to eat a fare amount more than I really needed. Sincerely thanks for the insight

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  9. The commentators who associate late night patterns with socioeconomic class etc may have a point, but there are also some of us who are biological night owls. I am sluggish in the mornings and energetic at night, regardless of how much sleep I get. I work ‘normal’ hours and I get up around 7.00am – but only because I set an alarm and have to walk across the room to turn it off. Left to its own devices, my body will wake me up around 11am. In fact, even when I’ve been up for hours, I can feel that my body really comes alive around 10.30am. I have consulted a sleep specialist about this, because I’m tired of feeling tired during the day, but I was told that shifting innate sleeping patterns is extremely hard to do, though I am attempting to do it at the moment.

    I find that if I am not rigidly disciplined about it, I will eat a lot at night, because that’s when I’m hungriest. This is despite having a regular meal pattern, including breakfast every day.

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