Thinking Thin Not So Easy

Our overweight population is arguable the most dangerous health crisis the United States is facing right now, and much of the rest of the developed world is heading down the same path. About 65% of the U.S. population is overweight, and over 30% are obese. Public awareness of this is rising slowly, resulting in half-hearted attempts by fast-food restaurants to add healthy items to their menus and in the proliferation of a diet industry that in many cases probably does as much harm as good. Needless to say, the trend seems to be continuing in the wrong direction. As we grow fatter as a nation, we also find diabetes, heart disease, and some types of cancer rising at alarming rates.

Many of the proposed solutions to this dilemma focus on public awareness and corporate responsibility, both of which are good things. Many scientists, however, are interested in finding the roots of the problem. There is a reason why human beings are inclined to eat fatty foods, and why the digestion of excess amounts of such foods results in the deposit of adipose tissue throughout the body. Think about this from an evolutionary standpoint. In an environment like that which our hunting and gathering ancestors lived, there were periods of food availability followed by days (or longer) where food was scarce. In this ancient world, the ability to store fat as adipose tissue would become adaptive, and the desire for fatty foods would have been beneficial as those types of food would result in stored energy that could sustain one over periods of scarcity. Today’s environment differs, however, in that food is available all the time, and those foods that are often the fattiest are those that require the least effort and money to obtain. Perhaps those behavioral remnants of our evolutionary past combine with the modern ubiquitousness of food to create the obesity epidemic we are witness to today.

But this obviously isn’t the whole story, for it doesn’t explain the difference between the 35% of the population who isn’t overweight and the 65% who are. Scientists hope that finding the reason for this disparity may lead to better methods to curb obesity and avoid the national health crisis we seem to be headed toward. There has been a great deal of research that supports a strong genetic influence in obesity. The number of genes involved, their interdependence, and the molecular mechanism of their influence, however, are yet to be determined.

Naturally some of research in this area is focused on the neural mechanisms that contribute to overeating. As eating is a rewarding process, much attention has been paid to dopamine abnormalities leading to obesity (for more discussion of dopamine and rewarding processes see last week’s post “Drugs, Love, & War: All the Same to the Brain?”). A recent discovery by William Bendena and Ian Chin-Sang of Queen’s University, however, has shown perhaps the most direct connection between neurotransmitter activity and overeating to date. Experimenting with worms that have distinct neurotransmitter similarities to humans, Bendana and Chin-Sang found a nervous system receptor that, when damaged, caused no change in the worms—until they were placed on food. Then they suddenly become lethargic, would not move away from the food, and gained fat at a much quicker rate than controls. When they added extra copies of the receptor to other worms, they became much more active, traveling great distances from their food supply. Of course much work must be done to apply these findings to humans, but it does suggest that perhaps there is a neurobiological mechanism that leads directly to lethargy and overeating. If so, it may be amenable to correction through pharmacological methods, which might be more successful than simply adding more salads to a fast food menu.