Many people confuse surveys of genes associated with diseases and the risk for diseases called nutrigenetics with the science that studies the effects of nutrition on genes called nutrigenomics.
While all humans are 99.9% genetically identical, the 0.1% difference is enough to determine the color of your eyes, skin, and many functions in the body such as how you break down drugs and phytonutrients.
So-called obesity genes are not actually individual genes except in those rare diseases where a single gene is totally defective resulting in severe childhood obesity. The vast majority of humanity has obesity susceptibility gene regions controlling the action of the actual genes that lead to forming proteins which could also be called “adaptation to starvation genes”. It is the rapid disconnect between our genes and our environment of excessive calories and sedentary lifestyles in an increasingly urban world that has led to the obesity epidemic. Sedentary lifestyles increase the impact of the so-called obesity genes while increased physical activity decreases the impact of the genetic predisposition to overweight and obesity.
There are many regions of our genes that control the susceptibility to obesity. The most studied of these regions is the so-called “FTO Obesity Gene” of which there are 19 forms identified with about 6 forms that increase obesity susceptibility. Over half of the world’s population have forms of a gene called the FTO gene making them susceptible to obesity and overweight. The reason these forms of the FTO gene are so common is that they help humans survive starvation. When these genes to survive starvation are inherited by individuals living in a society with high fat/high sugar foods, an epidemic of obesity and overweight results. However, the effects of the FTO gene are less pronounced in individuals with high levels of physical activity demonstrating how lifestyle can reduce the impact of susceptibility genes.
Nutrigenetics attempts to correlate these differences with the risk for common diseases. Each gene has two parts called alleles. One is inherited from your mother and the other from your father. As you can imagine, these studies make a lot of assumptions and simply indicate a potential risk of a disease or condition such as obesity.
One example of how different populations have different genes are the A, B, and O blood types. These occur with different frequencies in different populations, but the Blood Type Diet which attempted to assign different diets to different blood types has been totally debunked.
You cannot change your genes, but you can affect how those genes function in your body with balanced nutrition and a healthy active lifestyle. There are a limited number of clear examples of how nutrients and genes interact to affect substances in your body. A susceptibility gene does not mean you will definitely get that condition. Nutrigenetics only calculates a probability that you might get a disease, while nutrigenomics points the way to change your risk through diet and lifestyle.