8/12/2019 The Economist - Obesity 14-10-2010

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Oct 14th 2010Obesity - Does light make you fat? - Whennot just whatmice eat affects how much weight theyput on

Illuminating the cause of obesity

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 e ercise and modern man!s generally more stressful lot"

#omething else may soon be included in the list$ brighter nights"

%ight regulates the body!s biological clock&priming an indi'idual!s metabolism for predictablee'ents such as meals and slumber" (re'ious research has sho)n that, in mice at least, the genesresponsible for this can be manipulated so as to make the animals plumper and more susceptibleto problems associated )ith obesity, including diabetes and heart disease" It )as not kno)n,though, )hether simply altering ambient light intensity might ha'e similar effects"

* team of researchers led by %aura +onken of Ohio #tate ni'ersity has cleared the matter up" *sthey report in the Proceedings of the National Academy of Sciences , they e amined ho) nocturnallight affects )eight, body fat and glucose intolerance -the underlying cause of late.onset diabetes/

in male mice" They found that persistent e posure to e'en a little night.time light leads toincreases in all three"

To reach this conclusion r +onken split her murine sub ects into three groups" #ome )ere kept incages lit constantly, so as to resemble a ne'er.ending o'ercast day" * second group li'ed inconditions akin to their natural habitat, )ith 1 hours of o'ercast day.like light, follo)ed by eighthours of darkness" The remaining rodents )ere also e posed to a cycle, but the dark )asreplaced )ith a dim glo) e3ui'alent to the t)ilight at the first flickers of da)n"

O'er the eight.)eek period of the e periment the mice in the first and third groups gained almost05 more )eight than those e posed to the natural light.dark cycle" They also put on more fatand e hibited reduced tolerance of glucose, despite eating comparable amounts of food andmo'ing around ust as much"

The only thing that seemed to differ )as )hen the mice ate" In the )ild, mice are nocturnal"nsurprisingly, then, those in the 3uasi.natural conditions consumed only about a third of theirfood in the 6day7 phase" +or a mouse e posed to the t)ilight cycle, ho)e'er, the figure )as o'er5"

In a follo).up e periment, r +onken looked at )hether the timing of food consumption alonecould e plain the obser'ed differences" It turned out that those forced to eat during the 6day7&ie,

out of )hack )ith their biological clock&did indeed gain about 105 more )eight than those fed at6night7 -be it dark or ust dim/ or those )ith uninterrupted access to grub"

Ho) this might relate to people )ill re3uire further in'estigation" 8ice and humans arephysiologically alike, so a similar effect might be e pected for people, but the fact that mice arenocturnal and humans diurnal is a serious complicating factor" It is true, though, that the spread ofelectric lighting means many people eat their main meal )hen natural daylight is long gone&theob'erse of a mouse eating during daylight hours" *nd that tendency to eat late, though it hasne'er been tested properly, is belie'ed by many nutritionists to be a factor in putting on )eight"

9hen the full e planation for the modern epidemic of obesity has emerged, it is unlikely that the

spread of artificial lighting )ill be the )hole of it" :ut this )ork suggests it might be a part" 9henyou eat could be as important as )hat you eat"