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节食减肥族们，你减的是脂肪还是肌肉呢？美国《内科医学档案期刊》的一项研究表明：睡眠时间长能更有效地帮忙节食者们减少脂肪，并能减少饥饿感，而睡眠时间过短的话所减少更多的为肌肉，而非脂肪！

IRA FLATOW, host:

You're listening to SCIENCE FRIDAY. I'm Ira Flatow.

Up next this hour: weight loss and sleep. If you're trying to lose weight, you might want to start paying attention to how much you sleep because a new report this week in the Annals of Internal Medicine looks at weight loss and dieters who get different amounts of sleep.

And the study followed only 10 overweight people, who were all on a calorie-restricted diet. But the one difference, the only difference in this test was how much they were allowed to sleep.

Half the group got eight hours. Half the group got around five hours. Everyone lost weight, but those with restricted sleep tended to lose their weight from their muscle. The weight - they lost muscle instead of fat, and that's not what you want to do if you're trying to lose weight.

And this small study is one part of an intriguing puzzle that researchers are piecing together on how sleep affects your weight, and ultimately, your health.

And joining me now to talk about it is Dr. Michael Lacey. He's a neurologist and board-certified in sleep medicine. He is the medical director of The Atlanta Sleep Medicine Clinic at The Atlanta School of Sleep Medicine and Technology.

Welcome to SCIENCE FRIDAY, Dr. Lacey.

Dr. MICHAEL LACEY (Neurologist; Director, The Atlanta Sleep Medicine Clinic, The Atlanta School of Sleep Medicine and Technology): Good afternoon, Ira.

FLATOW: Was this a surprising finding?

Dr. LACEY: Well, actually, tantalizing, I think, is a better word, because we, in sleep medicine, for years - and this has been getting a lot more press in the last several years - we've recognized that people with chronic sleep deprivation have significant changes in their metabolism and the way their bodies behave and have a far greater problem with managing appropriate weight or losing weight, and in most cases, tend to be overweight if they are chronically sleep-deprived.

So what was interesting about this is it shows - even in people who are slightly overweight - that in a very short timeframe, you already start to see changes in the way the body operates and metabolizes calories and things. So, very interesting.

FLATOW: And the fact that you're losing the weight from your muscles is alarming, I would think.

Dr. LACEY: That's as you so aptly put, that's really not what you're going for.

FLATOW: Mm-hmm. And why should sleep change the way you lose weight - instead of from the fat, to put it - take it from the muscle?

Dr. LACEY: Well, the thing that we've noticed - I mean, of course, there's a kind of a very basic assumption, which is that people who don't get enough sleep and are therefore sleep-deprived tend to have decreased energy, which leads to decreased activity, which leads to an overall decrease in the calories that they burn.

But on a deeper level, we also know that it decreases general body metabolism, and it causes insulin resistance to occur, which then leads to greater depositions of adipose, higher blood sugars, weight gain and so forth.

But they - probably the most critical finding in this study showed that even with two weeks' sleep deprivation, that you start to already see changes in two of the most fundamental hormones regulating appetite and satiation, or feeling full and therefore decreasing appetite. And those hormones are called ghrelin and leptin.

FLATOW: Mm-hmm. And one makes you gain - makes you want to eat, and one makes you feel full.

Dr. LACEY: Correct. Ghrelin is primarily secreted from the stomach, and with sleep deprivation, you get increased levels of ghrelin, which stimulates appetite. And at the same time, the levels of leptin that would normally be present in the body, which is primarily secreted from the cells that make adipose - which are called adipose sites - leptin decreases. And leptin in a normal person would signal satiation and sort of make you not want to eat again until you are appropriate hungry after a certain timeframe and a certain number of calories had been burned.

FLATOW: So when you don't sleep enough, you start to feel hungry even when you're not hungry, you shouldn't be hungry.

Dr. LACEY: Absolutely.

FLATOW: And so you start to eat at times you would not normally eat. Just...

Dr. LACEY: And in some cases, people even change what they eat, because many times, what you'll see in a person who's sleep deprived is they will tend to snack more on high-carb types of foods and snacks in order to kind of buttress their general energy level in an attempt to kind of self-stimulate and keep themselves more awake.

FLATOW: 1-800-989-8255 is our number. Talking with Dr. Michael Lacy about a new study that talks about how much sleep that you need so that you don't start eating when you shouldn't be.

Is there did this study find how many hours you need? They put people on a five versus eight hours. Would six be enough? Does the study show?

Dr. LACEY: Well, you know, in most people, the average amount of sleep that one requires to feel well-rested is in the neighborhood of seven to seven and a half. And so they really, I think, went for what they knew was going to produce significant sleep deprivation by making a five-and-a-half-hour group.

FLATOW: Now, did these people gain weight at all? Or they just - they lost weight only from - mostly from their muscles. Is that the difference?

Dr. LACEY: Yes. In this cohort of, as you said, only 10 people - so one always has to be cautious about drawing grand conclusions from such a small sample -but everyone lost weight. It's just that the five-and-a-half-hour group, the weight that they lost over that period of time was primarily lean mass, as opposed to fat tissue.

So it showed that in already beginning to shift the balance of those hormones, that the way that the body deals with adipose tissue or perhaps (technical difficulties) kind of mobilizes energy changes, even in two weeks.

FLATOW: Let's go to the phones, 1-800-989-8255. Dan in Wewahitchka - is that right - Florida.

DAN (Caller): That's correct. Yup. Wewahitchka.

FLATOW: Hi. Welcome to SCIENCE FRIDAY.

DAN: Thank you very much.

FLATOW: Go ahead.

DAN: I just wanted to know about what truly is sleep deprivation? Is it when you, you know, get a bad night's sleep, you know, because the children are up? Is it because I watched too much TV at night and only get five hours? Or is it truly having sleep apnea, something medically wrong?

FLATOW: Good question.

Dr. LACEY: As a matter of fact, Dan, sleep deprivation occurs through a variety of circumstances. As you've said, I mean, almost everybody gets an occasional bad night's sleep because stress or money or their kids, or they're sick, or whatever. And that generally is not sufficient because sleep deprivation. Usually, one has to be fairly continuously sleep deprived for at least a period of several weeks, if not months, for the longer-term significant problems with sleep deprivation to occur.

DAN: Okay. And something that's always bothered me, the medical field that always seems like a badge of honor when you're a resident to, you know, do nights, you know, sleep in the hospital, sleep in closets. Do you find that effect on that type of professional?

Dr. LACEY: Well, there's no question. That's one of the reasons why, in the last year or so, there have been very specific criteria laid down in terms of how many consecutive hours an intern or resident is allowed to work because, as you said, in the old days, it was kind of a rite of passage to be able to say that you were up for 48 or 72 hours, and you would wear that badge proudly.

But the problem is that that would almost uniformly lead to someone - by virtue of being that sleep deprived - that could be judgment impaired, and not so good.

FLATOW: Thanks for calling, Dan.

DAN: As well as the health problems.

FLATOW: Yeah. Thanks for calling, Dan.

DAN: Thank you.

FLATOW: 1-800-989-8255. You know, we do have this epidemic of type 2 diabetes going around. Could sleep deprivation have anything to do with that? I know more people are up later at night, tweeting and podcasting and things like that. Could we be seeing something having to do with sleep deprivation affecting the diabetes epidemic?

Dr. LACEY: I think that that is a piece of the puzzle, because what we are seeing all tend to walk hand in hand is that we are, as a population, heavier, which then makes a person also tend to be more prone toward type 2 diabetes, as well as being more prone toward certain sleep disorders like sleep apnea.

And right now, the statistics suggest that up to 75 percent of the people - in the U.S., anyway - with sleep apnea, obstructive sleep apnea - where their airway closes down during the night and they have interrupted sleep from fighting for air or stopping breathing - that nearly 75 percent of people who have that condition remain undiagnosed.

So it has a pretty significant health impact in general, because not only does it predispose people to type 2 diabetes, but high blood pressure, premature cardiac disease, depression, anxiety disorders, a great many things.

Sleep deprivation cuts across a lot of areas in both medicine and psychiatric disorders.

FLATOW: Mm-hmm. Let's go to the phones. Jacoby(ph) in Louisiana. Hi. Hi, there.

JACOBY (Caller): Hi, yes.

FLATOW: Go ahead.

JACOBY: I've had chronic problems with my (unintelligible), problems with insomnia for many years. And one of the things I have noticed is that when I'm up late at night and I've got that desire to eat - and it's gotten to the point where sometimes I'll wake up in the middle of the night to eat something. And I see the two problems as related.

Dr. LACEY: Well, there's no question. I mean - and - but you remember getting up during the night to eat, correct?

FLATOW: He dropped out. Sorry.

Dr. LACEY: Oh. Well, there are some people who eat during the night as part of a disorder similar to sleepwalking, and people may have seen this and associate it with certain types of sleep medications and things, where people will get up and, with no memory of it, will sleep-eat and will discover in the morning wrappers or crumbs or things and not know how they did it.

But there is also kind of a - either out of boredom or compulsion or a way to kind of satisfy an urge or a drive, make yourself full so it's easier to fall back asleep - people will often develop that as a secondary habit as well.

FLATOW: Mm-hmm. 1-800-989-8255. Joe in Wilson, Wyoming. Hi, Joe.

JOE (Caller): Hi. Thank you. Interesting subject. Frustrating though. Assuming that you set aside enough time for sleep and you exercise and eat right, don't drink caffeine in the evening, et cetera, what are some ways to actually get the right amount of sleep if you don't, short of taking, you know, sleeping pills and medication, et cetera?

Dr. LACEY: Well, that's a great question, Joe. And it's - actually, it depends a lot on kind of what a person's routine is. We, in the area of sleep medicine, refer to kind of general sleep preparation and habits collectively as sleep hygiene. And that encompasses when you eat, the types of food you eat, what shift you work, when you exercise, how much time you allot to wind down, and also very important, what type of sleep environment you have, because, you know, it needs to be sufficiently dark, sufficiently quiet, the bed comfortable. Pets can be disruptive. Children can be disruptive. Noises outside can be disruptive.

And on top of all that stuff, the amount of sleep each person needs is variable. You know, there are what are called long sleepers that need literally nine or nine and a half hours of sleep every night, and for them that's normal. Whereas other people may only need four and a half or five hours' sleep, and they seem to function quite well. Einstein reportedly only needed four and a half or five hours' sleep, and it didn't seem to hurt him too much with respect to his intellectual capacity.

So it really comes down to kind of getting yourself ready to sleep, providing the optimum environment, ideally doing some kind of exercise so that you have natural, healthy fatigue, which makes it easier to sleep, and then managing stress as best you can. I mean - and that's just to get you to sleep.

FLATOW: Right.

Dr. LACEY: Then it's a whole separate subject, staying asleep.

FLATOW: This test - this study was conducted with just 10 people, correct?

Dr. LACEY: Correct.

FLATOW: What other - where is the right direction to go here, because you talked about the connection between two different kinds of hormones in the body. What do we need to know more about?

Dr. LACEY: Well, I think we need to have larger cohorts of different kinds of controlled subjects, you know? Because if you take a group of people that basically, they're healthy, they are not sleep deprived people, and for a very short period of time you look at them with the lone variable that you're changing being sleep, it's very interesting, the conclusions that are drawn.

But I think it just falls short of being a sufficient study size or different kinds of - coexistent medical conditions and things that would allow us to be able to more accurately make recommendations to people who have sleep apnea or who have diabetes or who have other conditions and things like that in terms of what the optimal way to manage their sleep, and what things we should be measuring in those kind of people. And you know, that's - this is really just kind of a jump off.

FLATOW: Yeah. We're talking about sleep deprivation this hour on SCIENCE FRIDAY from NPR.

I'm Ira Flatow with Dr. Michael Lacey.

A tweet from PSA2 comes in saying: Wondering if napping can make up for sleep deprivation-induced weight issues, or does sleep need to be in consecutive hours? You hear about, you know, people taking power naps and things like that. Does that make up for any sleep deprivation?

Dr. LACEY: Well, it in a short run can help to kind of catch you up a little bit. People who are chronically sleep deprived, it is very difficult to build in enough of a nap to make up for what you're missing. Now, having said that, a kind of short or power nap in the early to mid-afternoon, that can be a very physiological thing. And it - that tends to tamp down the natural lull that people often have later in the day. It can actually increase productivity in certain populations.

But, you know, then one starts to get back to kind of general work ethic and rules and things like that. And, you know, often that sort of thing is frowned upon. So a short nap can be very restorative and refreshing for someone short-term or if they do it on a regular basis just to give them a little late afternoon boost. But it's really not sufficient to make up for chronic, significant sleep deprivation.

FLATOW: Is there anything wrong with taking medication that will give you the seven or eight hours of sleep?

Dr. LACEY: Well, for people who have chronic insomnia that is not due to some other type of primary medical problem, like sleep apnea, which can also have insomnia kind of piggyback on it, or restless leg syndrome, which can cause people to have trouble falling asleep, or pain or - I mean, there's a great many medical conditions that lead to insomnia, and it's improper to treat the insomnia or put a Band-Aid on the symptom without treating the underlying condition.

Having said that, there are definitely people as a subset who just have difficulty falling asleep because their personality, the way they manage stress, they just have a difficult time relaxing, shutting their brain down, that sort of thing. And what we try to recommend for most of those people as an initial type of therapy is a type of behavioral counseling modification called cognitive behavioral therapy that encompasses self-relaxation techniques and biofeedback and that - all various sorts of skill sets that can actually be taught and mastered by people to help give themselves better sleep.

If you've done all those things and a person still is sleeping poorly, then the use of some type of sleep aid on an ongoing basis, while certainly not ideal from several standpoints, is something that we often find ourselves coming to as a last resort, because it's far better than being chronically sleep deprived.

FLATOW: Yeah. All right. Doctor, thank you for taking time to be with us today. Helpful information.

Dr. LACEY: You're very welcome. Thanks for having me.

FLATOW: You're welcome. Dr. Michael Lacey is a neurologist and board-certified in sleep medicine. He's the medical director of the Atlanta Sleep Medicine Clinic at the Atlanta School of Sleep Medicine and Technology.

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