Extra Credit for Friday, June 24: Obesity: Does light make you fat?: When—not just what—mice eat affects how much weight they put on.

Obesity
Does light make you fat?
When—not just what—mice eat affects how much weight they put on
Oct 14th 2010 | from the print edition

Although processed and fatty foods and lack of exercise are blamed for the obesity epidemic, recent studies have shown that another factor may be light nights. Since light regulates the body's biological clock which controls metabolism, brighter nights disturb the metabolism's perception of meal times and times for sleep. Laura Fonken of Ohio State University and her team of researchers examined how nocturnal light can affect weight, body fat, and glucose intolerance by conducting tests on mice; mice are like physiologically like humans but a large problem in the experiments is the fact that mice are nocturnal (awake at night) and humans are diurnal (asleep at night). Fonken arranged her mice into three cages for an eight week period: the first cage was lit constantly, simulating a never-ending overcast day, the second cage simulated a natural habitat, with 16 hours of overcast daylight followed by eight hours of darkness, and the third cage was also lit with 16 hours of overcast daylight, but the eight hours of darkness was replaced with a dim glow, simulating twilight at the first "flickers" of dawn. Over the eight-week period, even though they ate similar amounts of food and moved about just as much, the mice in the first and third cages gained 50% more weight than the mice in the second cage who were placed in a natural light and dark cycle; nocturnal light did affect weight, body fat, and glucose intolerance by increasing all three categories. The difference between each groups of mice and the reason why the mice in the first and third cages gained so much weight was not what the mice ate, but when they ate. Since mice are nocturnal, as expected, the mice in the natural condition only ate a 33% of their food in the overcast day part of their cycle, unlike the mice exposed to the twilight/dawn who ate over 55% of their food in the day part of their cycle. Even though the mice exposed to a day and twilight/dawn cycle did have eight hours of dim light, they did not have any time of complete darkness, and this really made a difference in their times of food consumption. Furthermore, Dr. Fonken observed that due to their disturbed biological clocks, the mice in the first cage that was lit constantly gained 10% more weight than the mice in the other two cages who faced light that simulated light and (semi)-dark cycles. Again, humans are mice are different because humans are diurnal and mice are nocturnal. Even so, like the mice that ate in the "day" due to the unnatural light in their environments, many humans eat their main meals late at night due to the spread of electric lighting. Although it has never actually been tested properly, many nutritionists believe eating late is a factor in putting on weight. Further tests are needed to prove this theory, but these experiments show that artificial lighting may be a part in weight gain.

http://www.economist.com/node/17248910