Why Are We Overweight? Part 5

An important message from the research I’ve summarized previously is that weight gain does not increase spontaneous physical activity as it would if homeostatic control of energy balance was present. Conversely, the positive energy balance that promotes body fat storage actually dampens the drive to be physically active because that drive is rooted in the need to procure food. This means that the very circumstance that makes us fat to begin with makes us more apt to continue to gain fat in the future.

After we eat, insulin is secreted into the blood stream to allow for nutrient uptake by our cells. Circulating insulin promotes leptin release and, collectively, these hormones suppress both the motivation to eat and the desire to be physically active. This makes sense because adequate energy has already been taken in, so there is no need to hunt for or ingest more food. Once more energy is required, insulin and leptin fall, which creates the desire to be active and find the next meal. Under these circumstances, circulation of the gut peptide ghrelin increases and this hormone stimulates appetite. Consequently, the most favorable conditions for satisfying the energy deficit are created because we desire food and that which is necessary to obtain it.

Insulin and leptin drive these natural reactions within our bodies because of a homeostatic brain reward circuit that responds to their presence. However, another circuit that acts concurrently doesn’t follow suit. Instead, the reward derived from the hedonic circuit is a function of the taste of the food being eaten and, therefore, the drive to eat is still present even if the prevailing energy deficit has been satisfied. Armed with this knowledge, it’s easy to see why the obesity epidemic is currently in full swing.

At the beginning of our lives, the slate is clean and we are all storing at least close to the appropriate amount of body fat. So where do we go wrong from here? Well, first off, once our growing years are over, body fat will only remain constant if energy intake equals expenditure. This would be no problem if circumstances were still as they were when the system was designed to operate as detailed above. For example, if a lot of energy had to be expended to get food and the food that was available was devoid of the social cues that we associate with mealtime and also was lacking what might be termed ‘excessive palatability,’ it’s a sure bet that energy in would equal energy out and the system would stay in balance. Consider, for example, the classic scene where the tiger runs down and eats the antelope: It is probable that the tiger used at least the energy contained in that meal in order to get it and while I’ve never dined in that manner, it’s also highly likely that the meal meant no more to him than other obligatory aspects of his life. Ever seen a fat tiger?

As homo sapien evolved and the lifestyle that we now know came into existence, a number of changes occurred that laid the groundwork for the obesity epidemic we currently face. For example, in order to procure food in the present day, we no longer have to expend much energy; instead, we drive to the supermarket, circle the parking lot to find the closest space and then travel a short distance up and down aisles that are designed to minimize our need to walk. In addition, if you take a good look next time you are in such an establishment, you might notice that many shoppers are not even fully supporting their body weight as they carry out this regimen. Instead, they are leaning on their shopping carts for support. And speaking of which, these are the same carts that no longer have to be returned to the front of the store once our groceries have been transferred. Those convenient cart corrals have obviated the need for that.

After our shopping is done and we get home, the next major difference between what was meant to be and what is becomes apparent. For us as humans, food is much more than a source of nutrition that allows us to maintain our existence. Instead, it provides a vehicle through which we socially interact and we can also reward ourselves by experiencing myriad flavorful tastes. Consequently, there are cues present that influence what and how much we eat that have nothing to do with energy balance and the amount of fat we have stored.

As man has evolved, changes in how we obtain and ingest our energy do not conform with our brain reward system that is designed to ensure appropriate food-seeking behavior. However, these changes are in line with another reward circuit that is based upon the pleasures associated with eating. Collectively, this likely comprises a major reason why we are getting fatter. But the good news is the evolution of man has also brought changes that can enable us to offset this unhealthy progression. Specifically, the ability to reason should allow us to make conscious logical decisions about the amount of energy we choose to ingest and expend throughout our day.    

This article was originally published in New Living Magazine, which can be accessed on-line at www.newliving.com.





Go back