4 Does light make you fat?
THE blame for rising obesity rates has been pinned on many things, including a more calorific diet, the spread of processed food, a lack of exercise and modern man’s generally more stressful lot. Something else may soon be included in the list: brighter nights.
Light regulates the body’s biological clock—priming an individual’s metabolism for predictable events such as meals and slumber. Previous research has shown that, in mice at least, the genes responsible for this can be manipulated so as to make the animals plumper and more susceptible to problems associated with obesity, including diabetes and heart disease. It was not known, though, whether simply altering ambient light intensity might have similar effects.
A team of researchers led by Laura Fonken of Ohio State University has cleared the matter up. As they report in the Proceedings of the National Academy of Sciences, they examined how nocturnal light affects weight, body fat and glucose intolerance (the underlying cause of lateonset diabetes) in male mice. They found that persistent exposure to even a little nighttime light leads to increases in all three.
To reach this conclusion Dr Fonken split her murine subjects into three groups. Some were kept in cages lit constantly, so as to resemble a neverending overcast day. A second group lived in conditions akin to their natural habitat, with 16 hours of overcast daylike light, followed by eight hours of darkness. The remaining rodents were also exposed to a cycle, but the dark was replaced with a dim glow equivalent to the twilight at the first flickers of dawn.
Over the eightweek period of the experiment the mice in the first and third groups gained almost 50% more weight than those exposed to the natural lightdark cycle. They also put on more fat and exhibited reduced tolerance of glucose, despite eating comparable amounts of food and moving around just as much.
In a followup experiment, Dr Fonken looked at whether the timing of food consumption alone could explain the observed differences. It turned out that those forced to eat during the “day”—ie, out of whack with their biological clock—did indeed gain about 10% more weight than those fed at “night” (be it dark or just dim) or those with uninterrupted access to grub.
How this might relate to people will require further investigation. Mice and humans are physiologically alike, so a similar effect might be expected for people, but the fact that mice are nocturnal and humans diurnal is a serious complicating factor. It is true, though, that the spread of electric lighting means many people eat their main meal when natural daylight is long gone—the obverse of a mouse eating during daylight hours. And that tendency to eat late, though it has never been tested properly, is believed by many nutritionists to be a factor in putting on weight.
1. People often attribute their overweight to the following factors except _________.
A. a highcalorie diet
B. the diversity of processed food
C. a lack of exercise
D. too much pressure
2. Light can _________.
A. reset the body’s biological clock
B. disturb the body’s biological clock
C. quicken an individual’s metabolism
D. regulate an individual’s metabolism
3. From the research led by Laura Fonken, we can see that _________.
A. continuous exposure to light during the night increases the weight
B. disordered biological clock can cause the weight problem
C. a little dim light has no effect on the weight
D. besides eating less people can lose weight by exercise
4. Many nutritionists believe that _________.
A. the spread of electric lighting does harm to people
B. eating during night can make people put on weight
C. the effect of the tendency to eat late in weight should be tested
D. natural daylight has nothing to do with overweight
5. The best title for the passage may be _________.
A. Light can Make You Fat
B. Stop Eating Under Light
C. Night Eating is Harmful
D. New Discovery in Food Nutrition
