Fat Mice: Should we eat in the daytime or at night?

Researchers at Ohio State University have been keeping the light on for mice–and noticing that it makes them fat. In an article published on line in the Proceedings of the National Academy of Sciences (Oct 2010), Fonken et al. reported that mice exposed to continuous light, even if only dim, gained 50% more weight than those housed with a normal light-dark cycle. Interestingly, their overall food consumption did not increase.

So, why did the extended period of light make the mice fat? In a subsequent experiment, where the mice were not given food during the day, they did not gain excess weight. That is, mice given access to food day and night gained more weight than those that only ate at night. Therefore, the extended periods of light did not make the mice fat; the extended periods of eating did. The light modified their eating patterns.

Next questions. Does this mean that we should get rid of our night lights? Or perhaps we should stop using artificial lighting at all? Answer. Not based on this research. After all, the work was done in mice, which are nocturnal creatures. Humans are diurnal. In addition, the light itself did not have much to do with the obesity. The behavior associated with continuous light did.

The researchers go on to suggest that perhaps “people who use the computer and watch TV a lot at night may be eating at the wrong time and disrupting their metabolism.” Maybe. But this is speculation, not results or even interpretation of results. The article says that “the findings show another possible reason for the obesity epidemic in Western countries.” Not true. The results show a reason for fat mice, not fat people. In addition, these mice were exposed to extended light, not dark. But, since we are active in the daytime, an equivalent experiment would have humans in continuous darkness. So, is it possible that we are obese because we light our homes? Yes. But this research does not speak to the issue in any significant way.