Wednesday, March 18, 2009
Sleep & weight loss
To sleep, perchance to dream – ay, there’s the weight loss
We all enjoy a good snooze because, well, because it just feels good. Awaken refreshed ready to tick off another successful day. Over the last five years we have also heard that a good snooze helps the waistline, which in itself doesn’t make much sense because your metabolic rate (and therefore kJ burn) is at its lowest.
However, if you sleep for less than 6 hours a night, then the stats tell us that you will be plumper than average. Does being overweight make you sleep poorly, or is it the poor sleep making you overweight? There is a suggestion that lack of sleep upsets the balance of certain hormones that control your appetite.
What hormones would they be?
Grehlin and leptin. The levels of grehlin tend to go up and the levels of leptin come down with lack of sleep. This is a problem because grehlin is an orexigenic hormone while leptin is anorexigenic. No, I hadn’t heard of the term ‘orexigenic’ either, until about 10 minutes ago. Orexigenic means it has a stimulating effect on the appetite. An ideal word for casual use at the dinner table (“Thanks, honey. This meal looks particularly orexigenic”). Anorexigenic is the opposite: it dampens the appetite. Of course, you have heard the term anorexia in a different context.
Sleep & hormones
The researchers, who used the word I had never heard of, decided to slice three hours off the regular sleep time of 11 adults, 5 women and 6 men, and track their eating and hormone levels for two weeks. This was done in a sleep laboratory so no cheating was possible. Three months later, the measurements were compared to when the subjects got their regular sleep. Again, that was done in a supervised laboratory.
Surprisingly, there was little difference in the hormone levels between regular sleep and sleep deprivation. The amount of kilojoules burned each day and the amount of kilojoules eaten at meals didn’t differ either. What did change was the extra kilojoules eaten at snacks. Getting only 5 hours sleep a night meant they ate about an extra 850 kJ (200 Cals) more, with most of it coming from evening snacks.
What does it all mean?
That depends on your viewpoint. It does support previous research suggesting that sleep deprived people eat more food, and therefore become fatter. However, it doesn’t support the notion that it is all due to hormonal changes. Something else could be playing a role. As you all know, a study of 11 adults won’t give you a proof of anything, just an indication of where to direct future research.
And then there was the little problem of the subjects – they were humans. You put humans in a situation like this where they have unlimited “free” food, then they eat more than they need. Which is precisely what they did in this study, whether they were sleep deprived or not. It is the Qantas Club or smorgasbord phenomena. When humans see “free” food they just load up their plates. I mean, who knows, there could be a famine in, gee, 10 minutes. Now you see why it is so much easier to study rats – everyday is the same and the lab always provides free food and accommodation.
Reference: American Journal of Clinical Nutrition 2009; 89: 126-133.