When you eat matters

A very interesting study has just been published in the journal Obesity. The work, by Arble and colleagues in the Turek laboratory, fed mice high-fat food either during the day or at night. The surprising result was that mice fed during the day put on 20% more weight than mice fed at night. In both cases the mice had unlimited access to food yet both groups of mice ate the same amount, so there was no difference in net calories. Instead, what this result suggests is that the body deals with calories differently at different points of the diurnal cycle. During the active phase (night for mice) calories are shifted into burn mode, while during the resting phase (daytime for mice) calories are stored with greater efficiency.

If this result can be translated into humans it would suggest that large meals should be concentrated in the active phase of the day, breakfasts and lunches, and that evening or night meals should be restricted. An interesting proposal is that the American evening-biased eating rhythm compared to the European lunch-biased eating rhythm is partly responsible for the obesity problem in America. Of course it could only ever be a fraction of the problem, as many other correlates with obesity are well recognised. For example, a study by Pickett and colleages has demonstrated that countries with higher income inequality have higher calorific intake and obesity, and another study by Bassett and colleagues points out that Belgians burn 62 extra Calories per day by walking and cycling, compared to a poor 20 Calories per day by Americans.

The other important aspect of this study is that it contributes to the growing body of evidence dispelling the simplistic "obesity = too many calories and not enough exercise" formula. As published by the Segal laboratory, the majority of difference in body mass index (BMI) is due to genetics (64%). Being overweight does not mean that an individual is making worse eating or exercising decisions than a healthy range individual - the majority of the difference in weight just comes down to the fact that different genetics leads to different metabolisms.

Comments

[Lydia]

In the final paragraph, Segal et al remind us that the factors shared by twins raised apart consist of both shared genetics and a shared intrauterine environment. It will be interesting to study humans derived from donor embryos to tease apart the difference between these two factors.