Eating After Dark
Few of us (shift workers excepted) realize the degree to which our sleeping patterns affect our weight. But this week, a well-designed study shed some light on how the absence of darkness while we sleep may contribute to weight gain, at least in mice. It may be that "a calorie is not always a calorie" when the biological clock is upset by exposure to light. Or, perhaps, the time when food is eaten may be more important than was previously thought.
Staying Up Late
With the invention of the light bulb at the start of the 20th century, humans became exposed to unnatural light at night. Now, besides staying up after nightfall, people commonly fall asleep with lights on from TVs, computers, other gadgets, and outdoor lights. Dr. Laura Fonken and her colleagues at Ohio State University wondered if there was a parallel between rising obesity rates and levels of light at night, and so they designed a series of experiments to test that hypothesis. The results were reported in the October 11, 2010 online edition of the Proceedings of the National Academy of Sciences.
Weight Gain and Sleep
The scientists exposed three groups of mice to different light cycles. Group-1 was exposed to 16 hours of bright light and 8 hours of darkness; Group-2 was exposed to 24 hours of bright light; Group-3 was exposed to 16 hours of bright light and 8 hours of dim light. The three groups of mice ate the same amount of food and got the same amount of exercise, but the mice in Groups-2 and -3 gained almost 50 percent more weight than the mice in Group-1 and they experienced a rise in blood sugar too. The dim illumination was akin to having a portable TV in a bedroom.
Eating Instead of Sleeping
The researchers noticed that the mice exposed to light ate more than half of their calories during normal sleeping hours, and so they went back to the lab to control the time when the mice ate. The three groups of mice were exposed to the same differing light cycles, but the time when they ate was controlled. It turned out that the mice in Groups-2 and -3 did not gain weight when their mealtimes were restricted to normal activity hours. What mattered more than light was timing of meals.
The bottom line: It is much too soon to extrapolate the results of these studies to humans, but it is interesting to think about whether weight gain and glucose control is related to when calories are consumed. Light probably disrupts the biological clock, and when that's combined with nighttime eating, weight gain and blood sugar problems may ensue. Make eating after the sun goes down an exception and not the rule.
Are you concerned about eating after night fall?