Overweight and obesity: just a simple in and out computation?

I want to pose a simple question: why do people become overweight and obese?

If, like me, you thought the simple answer was something like: 'because people eat too much and don't exercise enough' you might think you were right and that's it; the issue is solved by that simple equation: food in = energy in, exercise out = energy out. But what if it just wasn't that simple. What if there were maybe other factors which influence our relationship with food?

Two studies have caught my eye in recent days related to just this question. The first is this one from the University of Otago in New Zealand published in the BMJ. The basic premise of the study was to ascertain any relationship between sleep and weight (as measured by body mass index, BMI and body fat). The authors followed 244 children from age 3 to age 7 taking regular anthropometric measures (height, weight) and body fat measures. At the same time, sleep duration and physical activity were measured again at regular intervals.

Before I get to the results, I will ask another question: what would you expect to happen? Would you perhaps expect those who slept longer, and hence were physically less active for greater periods of time, to show a higher or lower BMI than those who slept less? Well, if you thought that longer sleeping time was associated with higher BMI... you would be wrong. The authors actually found that less sleep was associated with higher BMI alongside other studies examining this issue.

Why? Well the obvious answer would be that with more time awake, there was more time to do things like eat. The only problem with this argument is that dietary intake was controlled for during this study, alongside other variables such as birth weight, maternal smoking during pregnancy and quite a few other variables that could have potentially impacted on results. The results suggested that each additional hour of sleep between the ages of 3 and 5 were associated with a BMI reduction of 0.49 at age 7. The explanation for the results seemed to lie in what happened to fat in the body and its accumulation.

The second study is this one which relates to a doctoral thesis delivered at Lund University in Sweden. The student, Caroline Karlsson, reports that comparisons between rats fed so-called 'good' bacteria (in this case the aerobic species, Lactobacillus plantarum HEAL 19) against those fed inflammation-causing Escherichia coli (E.coli) seemed to account for differences in weight gain when eating the same type and quantity of food. More 'bad' bacteria = more weight gain - at least in rats (although interestingly the differences between bacteria type just missed significance, p=0.086). Similar observations have been made in other studies adding to the increasingly wider role that our gut bacteria seems to play in maintaining health (and disease).

Going back to the original question then: why do people become overweight and obese? These studies imply that to maintain that healthy weight it might not just be a case of monitoring what goes in and what comes out. Getting plenty of sleep when you are a nipper and perhaps keeping an eye on your gut bacteria before tucking into that full English might be important factors also. How such findings relate to autism and other conditions where early sleep patterns might be impaired and gut bacteria aberrant in some cases, is perhaps the next question to be asked.