Fat on the Belly: Whose Business?

Fat on the Belly: Whose Business?

Deep fried chicken, hamburger, ice cream, cake… After eating in America for seven months, I found myself in a body weight crisis for the first time in my life. Before coming to America, I’ve never worried about my body weight or diet – though my appetite seemed to be a bit better than most other women, my body weight stayed relatively stable. “You are just like everyone from your dad’s family, staying thin even when eating a lot.” My mom always commented. But this time, even my dad’s chromosomes can’t save me from picking up fat on my belly.

Apparently I’m not the only person who is having trouble controlling her weight. According to World Health Organization (1), over 1 billion people worldwide are overweight – with a body mass index above 25 – and at least 3 million of them are obese – with a body mass index above 30 (for more information of calculating body mass index, see (2)). In the United States, with 68% of adults being overweight and 33.8% obese, the problem of obesity has raised great public health concern (3). Many scientific researches have been done on the causes of body weight change, as well as our body weight regulation mechanisms.

A frequently discussed theory among them is the set point theory. It was first proposed in 1977 by Mrosovsky and Powley, suggesting that in many animals, body weight is controlled by a negative feedback system (4). Hypothalamus plays the central role in the system; it detects changes in body fat depot, and response to it by producing hormones to stimulate related organs. The body then changes food intake to compensate the fluctuation of body weight. The theory has been reviewed and interpreted in various ways after its publication. Nowadays we know that the “set point” is not simply a feedback loop, but a series of complex interactions between nutrient selection and metabolic responses to diet, as well as environmental and genetic factors (5). The set point theory brings a new perspective to our understanding of body weight: our conscious selves may not be as powerful over our weight control as we usually think them would be. This time, our bodies work at their own will, and it is no more “our” business.

However, although the set point theory is useful for us to understand how our bodies maintain a relatively stable weight, not all body weight related observations can be explained very well with this theory. For example, recent studies found that under chronicle stress, our body fat distribution will change, resulting in increasing fat storage on the abdomen. Our current interpretations of set point theory tend to make us think that our body weight regulation is an endocrinal process, over which our conscious self has no control. However, this study suggests external factors such as stress may also greatly influence our body weight – so maybe we are not that powerless in changing our weight.

To discuss the implication of this study, we need to first answer this question: is changing fat distribution a function of the set point system, or it is a standalone regulation system?

One possibility is that the set point system may consist of several different subsystems. A central part may be in charge of controlling the fat distribution, while the subsystems follow the order from the central part. If one subsystem increased its weight, the other parts of the system would decrease their fat storage in order to keep the body weight constant. Although a study (5) shows that the proportion of different kinds of body tissues in rats changes in under- or over-feeding condition, it seems that no research has been done in the proportion change of fat tissue in different body parts. And since the change in fat tissue weight seems to be already compensated by change in other body component, the adjustment of fat distribution might be unnecessary for the set-point system.

It is also possible that another regulating mechanism is present in addition to the set point system. If this is the case, then a body part might gain weight without changing other parts of the body. Studies have shown that glucocorticoids, a class of hormones related to stress-induced activities, can act on muscles and skins’ fat storage and promote abdominal obesity (6). This result can be interpreted as a proof of the presence of mechanism that indirectly affects body weight distribution. This type of indirect mechanisms, however, may not fit into the category of body weight regulating system, for these mechanisms usually have other more profound effects on our whole body and their effects on body weight may be relatively insignificant. Also, this hypothesis is rather counter-intuitive – when someone is gaining weight, instead of only having fat accumulating at the abdomen, he/she usually will at least show some changes on his/her arms, face, etc.

If we associate the research with our daily life experience, we may come up with another hypothesis: the problem of prevalent obesity comes from our set point system’s failing to adjust. It’s probably still working – maybe even working hard – but its effect is out-weighed by the influence of the outer world. Development in modern industry has been changing our life in an incredible speed – much too fast especially in the evolution timeline. Our nervous system, digestive system, and endocrinal system are designed by evolution to adapt to natural food sources that are relatively low in energy. But in industrialized societies, those foods are replaced by highly processed, energy-dense, fat or sugar based foods. Conceivably, the excessive calories we take can easily become a burden for our bodies’ weight control system – we don’t have enough time to evolve a more efficient “fat-burning system”, but look how much more calories we have to burn to stop them from becoming body fat! Studies show that obesity is much more common in industrialized countries, whose main cause is the easy access to energy from food (1). To make things worse, many things we commonly have, such as stress and lack of exercise, can further disrupt our body’s physiology and weaken its ability to react to the outside stimuli.

It’s about time to give a second thought on “our” control over our bodies. We cannot change the biological processes inside our bodies, while we can change the output of those processes by adjusting the input – and that is our behaviors. Changing eating habits in both food quantity and quality, doing more physical exercise, leavening mental condition, etc – these changes may all contribute to reducing the load on our already stressed body weight regulation system. The set point theory may seem to put us in a passive role in weight control, but from another perspective, it is a reminder of what we need to be active about. When gaining weight, don’t always blame our bodies – it is our business.

References

1. "Obesity and overweight." World Health Oraganization. Available from http://www.who.int/dietphysicalactivity/publications/facts/obesity/en/. Internet; accessed 8 April 2010.

2. "Calculate your BMI." National Heart Lung and Blood Institute. Available from http://www.nhlbisupport.com/bmi/. Internet; accessed 8 April 2010.

3. "WIN - Statistics." Weight-control Information Network. Available from http://www.win.niddk.nih.gov/statistics/#overweight. Internet; accessed 8 April 2010.

4. Mrosovsky, N. "Set points for body weight and fat." Behavioral Biology 20 no. 2 (1977): 205-223.

5. Harris, Ruth B. S. "Role of set-point theory in regulation of body weight." The FASEB Journal 4 (1990): 3310-3318.

6. Dallman, Mary F.. "Chronic stress and comfort foods: self-medication and abdominal obesity." Brain, Behavior, and Immunity 19 no. 4 (2005): 275-280