Do Nighttime Calories Count More Than Daytime Calories?

An interesting phenomenon of our times appears to be the number of people who consume the majority of their daily calories in the evenings or at night. I have previously blogged about the importance of eating regularly and not skipping meals, as this can promote homeostatic hyperphagia (overeating in response to hunger).

But new research suggest that there may be more to night-time eating than just an increased chance of overeating – it may well be that calories eaten at night are more likely to be stored as fat than the same amount of calories eaten during the day.

This notion is supported by a fascinating new study in mice by Deanna Arble and colleagues from Northwestern University, Evanston, IL, to be published in next month’s issue of OBESITY.

Based on a number of recent studies in animals linking energy regulation and the circadian clock at the molecular, physiological, and behavioral levels, Arble and colleagues examined the possibility that the timing of food intake itself may play a significant role in weight gain.

In their carefully conducted study, the researchers fed two groups of mice a high-fat diet with the same amount of calories for six weeks. The only difference between the groups was that one was fed at night (the normal eating time for mice, who are nocturnal), the other group was fed during the day (normally bedtime for mice).

Despite eating the same amount of calories and no change in activity, the mice fed during the day weighed 20% more at the end of six weeks and ended up with about 8% more body fat than the night-fed mice.

Thus, this study shows that simply changing the time of eating, without changing the number of calories can greatly affect body weight.

Although total calories and activity were not statistically different, there was a small trend towards more food intake and less activity in the day-fed mice, which may in the end have explained some of the difference, but by no means all of it.

Although the mechanism behind day-fed weight gain in mice is unknown, body temperature, satiety hormones and (lack of) sleep could contribute to this finding.

These findings, suggest that the synchrony between circadian and metabolic processes may play an important role in the regulation of energy balance and body weight control. As pointed out by the authors, “this study is the first to show causal evidence that feeding at the “wrong” time can lead to weight gain”.

If the same holds true in humans (and I can think of no reason why it shouldn’t), then eating when you should be asleep could be a key factor in promoting weight gain – something that all evening and night eaters may have to consider.

Edmonton, Alberta