A problem of our time.
Obesity is one of the greatest public health challenges of the 21st century. The prevalence of obesity has tripled in many countries since the 1980s. The problem is not with obesity itself per se, but with the accompanied increased risk to a whole host of nasty diseases, including type 2 diabetes, heart-disease, high-blood pressure and certain types of cancer. These dramatic changes have occurred against a constant gene pool and well within the lifetime of most of you reading this. This would put the smoking gun in the guilty hands of ‘environmental changes’, an all encompassing term used to describe changes in lifestyle, diet and working practices. The ONLY way you can gain weight, is if you eat MORE than you burn. The first law of thermodynamics, ‘Energy can be neither created nor destroyed. It can only change forms’, is paramount.
Genes and obesity
However, it is also clear that different people have responded differently to these changes in environment. Some have become over-weight or obese to varying degrees, while others have not gained a single ounce in the past 25 years. Studies from twins have estimated a heritability of weight to be somewhere between 40 and 60%. What might be surprising to most however, is that this heritability is equivalent to that of height!! No one disputes the fact that height is genetically determined; Tall parents = tall children. It is also well known that human beings today are taller than humans just a century or two ago. Why have we become taller as a species? Change in diet, environment, and lifestyle. It is the same argument with body-weight. We are now more obese because of changes to our diet, environment, and lifestyle. But it does not change the fact that if our parents are over-weight, we are more likely to be overweight. Simply put, we have become obese because we eat too much; BUT how obese each of us becomes is powerfully genetically determined.
Obesity, it’s all in your head!
Where there are genes, there are molecules to identify and biology to study. In the past two decades, tremendous progress has been made in understanding the mechanisms controlling food intake
. We now know of many hormones that circulate in the blood and signal to the brain our current nutritional status. Some, like leptin, inform the brain of how much fat we have, while other hormones secreted from the gut, reflect how much and what we ate in our last meal. The brain uses this information to make decisions about how much we should eat in the next meal. We are studying more about how this happens, trying to determine whether it differs between lean and obese people, and whether we can target any of these molecules to treat obesity