Monday, September 27, 2010

Sleep Duration and Adolescents' Fat and Carb Intake

Another article in the September edition of the Journal Sleep is about how short sleep durations can change the dietary habits of adolescents. The authors begin by pointing out the lack of data quantifying sleep duration and caloric intake. There is an association between sleep loss and obesity, especially in adults. The question is if it's due to increased caloric intake, decreased physical activity, or the same diet, but just altered metabolism.

The researchers measured sleep times in older adolescents with a watch-like device called actigraphy, which can measure sleep at home. They did this during the weekdays only, as weekend sleep times were too variable. They asked the adolescents to recall what food they had eaten, the portions, the percent of fat and carbohydrate, and snacking. They defined short sleepers as getting less than 8 hours of sleep, which is one hour less than the recommended 9 hours per night for adolescents.

The results showed that the average sleep time was 7.55 +/- 1.14 hours and 34% slept at least 8 hours per night. The median caloric intake was 1917 calories, 51% carbs, and 35% fat. If an adolescent slept <8 hours per night, they tended to be obese rather than non-obese. Also, if the adolescent slept <8 hours per night, they had a 2.7% increase in fat consumption and a 3.7% decrease in carbohydrate consumption than those that slept >8 hours.

Those that slept <8 hours / night had a 2.1 fold increase in the odds of eating a high-calorie snack. For each 1 hour increase in sleep duration, the odds of a high-calorie snack decreased by 21%. This was most prominent in girls.

The authors acknowledge the small differences in fat and carb intake, but point out that small increases tend to accumulate and could increase obesity rate.

As I've said in another post, childhood obesity is not caused by short sleep duration. In my opinion, people who sleep less and are obese have extra weight because they have more wake time to eat. Obestity is caused by increased consumption of high-calorie foods rich in salt, sugar, and fat. The food tastes good, so kids eat it, and eat lots of it. They also don't exercise much, as our society is so sendentary. And thinking that if you get an extra hour of sleep, you can magically shed extra weight without serious dietary change is unrealistic.

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