Have you ever walked into the cardio room of the Athletic Center and seen that same person on the elliptical machine for hours a day, attempting to achieve what the media calls a "perfect body"? How about that guy in the weight room whose veins appear to be popping from his forehead as he grunts to elevate the 50-pound dumbbells, but week after week his arms remain the same size?
There is a big difference between being "fit" versus being skinny or muscular. Having big muscles might require a lot of exercise, but scientists have begun to discover that an individual's genetic background can contribute as much as lifestyle to his or her overall level of fitness.
Body structure and weight do not only reflect eating and exercise habits but also potentially the influence of one or more genes. Genes are small lengths of DNA, inherited from your parents, which direct physical development and behavior.
Some genes tell your body how to metabolize food and where to store fat. A number of people are genetically inclined to burn calories slower than others. It is important to remember that this is a predisposition, not an absolute diagosis; metabolism can be changed by diet and activity as well as by genes.
It is easy to see that being overweight or thin can run in families, but it is difficult to determine how much is purely based on genes since individuals in a family often have similar eating and exercise habits.
Scientists have attempted to discover the genetic causes of weight gain for years, but it has turned out to be a complex problem with many factors. One of the first contributing factors to be discovered is the hormone leptin.
Leptin is produced by adipocytes, specialized cells that store fat. It is thought to act as a lipostat, a compound that regulates fat intake by telling the brain how much fat is already in the body. As the amount of fat stored in adipocytes rises, leptin is released into the blood and signals to the brain that the body has had enough to eat.
Leptin regulates appetite in all individuals. Recently, a sample of obese children was found to have mutations affecting the gene coding for leptin. Without leptin, children have a massive and uncontrollable appetite, which can lead to significant weight gain.
In a recent study, scientists from Imperial College London have discovered another gene that may increase the risk of obesity. In an examination of more than 1,200 people, the gene GAD2 stood out as a regulator of appetite.
Scientists have identified two forms of the GAD2 gene that work in opposite directions. One form protected against obesity by keeping appetite within normal limits, while the other made it more likely by abnormally stimulating the appetite.
GAD2 works on a pathway in the brain that integrates information from the gut and nervous system. The neurotransmitter GABA, or gamma amino butyric acid, can lead to increased appetite in this system. GAD2 speeds up the production of GABA.
Like many other human traits, obesity is probably influenced by a complex group of genes. Scientists estimate there may be upward of 250 genes linked to obesity and many more associated with other elements of body type such as muscle size or strength.
Genetic influence is important, but genes are not the only determinant of body type. Genes interact with each other and with thousands of environmental factors, so even if a person has a genetic predisposition to being overweight, his lifestyle ultimately determines whether he is generally healthy.
A good example of this is evident when people try to lose weight in trouble spots like hips or thighs. If you have a genetic predisposition to store more fat than usual, and then you try to fix the problem by severely restricting calories and increasing the duration of aerobic exercise, your body will protect itself by going into "starvation" mode. If you continually starve your body it will attempt to conserve fuel, increasing its amount of stored fat. Where does that fat go? It winds up precisely where you do not want it: your problem areas.
It is genetically impossible for everyone to be thin, but is possible to be "in shape" and healthy. Exercising on a regular basis and eating a well-balanced portion-controlled diet will eliminate excess body fat even in those predisposed to be overweight.
These lifestyle factors can also overcome a genetic predisposition toward health complications such as diabetes, high blood pressure and stroke. All three, which are among the most common diseases affecting Americans, have been linked clinically and genetically to obesity and poor fitness.
When it comes to your body, there are things you can change and things you cannot. In the end, the way you treat your body and the way you think about it are much more important than the traits you may have inherited. You are still in control -- your health is still up to you.
