More evidence that weight control is determined by much more than ‘calories in/calories out’

Share This Post

There’s no shortage of awareness about the burgeoning rates of overweight and obesity afflicting Westernised countries. There are two principle theories about what causes obesity:

1.     It’s all about calories in/calories out

Proponents of this theory state that body weight is simply a function of the calories we put into our body (food and drink) and those that are burned during the processes of metabolism and activity. This theory is very much a conventional view, and has underpinned weight management advice for several decades.

2.     It’s more complicated than just calories

Some say that calories in and out does not adequately explain the burgeoning rates of obesity. The idea here is that there are hormonal (and perhaps other) factors that predispose towards deposition of fat in the fat cells that go way beyond the simple ‘calories in, calories out’ theory.

Just for the record, I’m a believer in the second theory. One reason for this is that science shows that taking a purely calorie-based approach to weight loss very rarely yields any significant success in the long term. And I’ve met hundreds of people who attest to this too. On the other hand, I’ve seen many, many individuals forget about calories, eat properly, and lose excess fat in a way that is sustainable in the long term.

The other thing is that there are some experiments that suggest that body weight is simply not all about calories in and out. For example, just over a year ago I wrote about a study in mice that found that mice eating when the would normally be asleep or inactive got fatter than mice eating at normal times. The surprise (for some) was that this greater weight could simply not be explained by the calorie principle.

Such a study is unlikely to be as relevant as a human study. However, in the absence of relevant research, there is no doubt that animal experiments of this nature ask serious questions about the validity of the calorie-principle, and strongly suggest other important factors affect body weight.

I was very interested to read another study published this week that is in a similar vein.

This study, again in mice, assessed the relationship between light exposure and body weight [1]. Mice were kept in one of three different lighting conditions:

1.     16 hours of light and 8 hours of dark per 24 hours (to simulate ‘normal’ light/dark phasing)

2.     24 hours of light

3.     16 hours of light, followed by 8 hours of ‘dim light’

This last condition is perhaps most interesting, as it sort of parallels the human condition where we can be exposed to light (street lights, domestic lighting, LED displays, etc.) when we are asleep (or should be asleep).

Food intake and activity was also assessed in all the mice. The results showed that, over time, mice kept in conditions 2 and 3 got significantly fatter than those in conditions one. In other words, exposing mice to light at times when it would normally be dark led to weight gain.

Well, perhaps the explanation is that these mice ate more and exercised less. Actually, the results did not support this idea. So, again, we have evidence that something other than ‘calories in and calories out’ has influenced the weight of these mice.

One other factor that was different was the timing of eating. Relatively speaking, mice exposed to dim light ate proportionally more during the light phase of their day than mice living under ‘normal’ conditions (condition 1). Mice are nocturnal animals, and generally do their eating at night. In short, therefore, there was an association between eating at a time when eating is not usual and enhanced weight gain. This result is consistent with the results of the study linked to above.

In an effort to probe further the relationship between the lighting conditions, eating pattern and weight, the researchers restricted the food supply to when the mice would normally eat (night-time). When they did this, mice did not get significantly fatter.

In summary, therefore, exposing mice to light at night caused them to eat more at an abnormal time (during the day), and this appeared to cause weight gain in a way that was not explained by caloric balance.

Now, if we were to apply the same concept to humans, we might be open to the principle that ‘unnatural’ light exposure could lead to eating at abnormal times which could lead to enhanced risk of obesity. In the case of humans, we might want to avoid over-eating in the evening.

I generally counsel against big meals in the evening. A couple of strategies tend to work well here, without the need for constraint:

1.     Eat breakfast (preferably a protein rich one)

2.     Have a snack of something satisfying (such as some nuts) in the late afternoon or early evening


1. Fonken LK, et al. Light at night increases body mass by shifting the time of food intake. Proceedings of the National Academy of Sciences. 11 October 2010 [epub before print publication]

More To Explore

Walking versus running

I recently read an interesting editorial in the Journal of American College of Cardiology about the relative benefits of walking and running [1]. The editorial

We uses cookies to improve your experience.