Both nutrition and genetics affect metabolic processes. Because of differences in the genetic makeup of individuals, the effects of nutrition on metabolism vary from person to person.
For a given metabolic parameter, some people can be said to be diet responsive. This means that the diet has a major effect on the expression of this particular parameter. Other people are diet- resistant. A good example of this difference is found for the blood cholesterol. In some persons, a diet that is high in saturated fat (animal fat) and cholesterol will produce a striking increase in the blood cholesterol level. In others, the effect will be minimal. This individual variation in response to diet extends to many other metabolic parameters.
One goal for the study of diet responsiveness is to lay to foundation for understanding its genetic basis. In other words, investigators have been searching for "genes for diet responsiveness". Some progress along these lines has been made in research in experimental animals. In humans, little headway has been made so far.
Nonetheless, continued research is justified for several reasons. First, if a gene for diet responsiveness can be discovered, this gene must be a key regulator of metabolism. It could become a target for drug therapy. The discovery of such a gene would be the first step on the road to drug development. Second, the finding could have clinical application.
It could be that a "diet-responsiveness gene" will connect beyond individual metabolic parameters to disease processes. For instance, a gene that causes dietary saturated fats and cholesterol to induce a marked rise in the blood cholesterol level may predispose to coronary heart disease. Finally, the concept of diet responsiveness could promote the bring the importance of individual variation into clinical practice.
Most dietary recommendations are made on the assumption that everyone responds in the same way. However, if individuals vary in their responsiveness to diet, the dietary prescription may have to be modified for persons who are diet responsive or diet resistant. Although the primary focus in the study of diet responsiveness is to determine its genetic basis, it must be recognized that other factors also can affect responsiveness. For example, the presence or absence of obesity could be important.
Since obesity has a profound influence on metabolism, it could either increase or decrease the metabolic responsiveness to individual nutrients. Other acquired factors, such as drugs, also can affect how the body will respond to a change in diet.
In the past, Dr. Margo Denke, a former faculty member in the Center for Human Nutrition, was especially interested in the issue of diet responsiveness. She focused mainly on the effects of the dietary factors on the serum cholesterol levels. More recently, the emphasis of the Center has shifted to the interaction of overnutrition (and obesity) on genetics in causation of the metabolic syndrome.