W. Thomas Johnson
When I opened the February 16 issue of the journal Science, I was awestruck. There, in front of me, chromosome by chromosome, was the human genome--nature’s instructions for making a human being. Although the genome is only a rough draft--about 90 percent complete-- its publication in Science and also in the journal Nature is an event of enormous magnitude. It marks the beginning of a revolution that will precisely define the foundation underlying human health and disease.
Knowing the sequence of genes that make up the human genome is a huge step in understanding how our genetic makeup influences our biological function. However, much work remains to identify specific genes and to understand how they interact with each other and with environmental factors to influence our health. As a scientist who studies the relationship between nutrition and disease, I am particularly interested in how knowledge relating to the genome will influence the future of nutrition research and the establishment of dietary guidelines.
The term environmental factor often has a negative connotation, conjuring up IMAGES of pollutants, pesticides and various other toxins injurious to health. However, the nutrients in the foods we eat also are environmental factors that can interact with our genes and alter the way they regulate our biology. For example, eating cauliflower or broccoli can "turn on" a set of genes that help detoxify chemicals that can cause cancer. Even though scientists have identified some of these interactive genes, they still cannot assess how much the interaction lowers an individual’s disease risk. In other words, a person may still develop cancer in spite of eating cauliflower or broccoli every day, and presently, science can’t predict who that person would be.
As more becomes known about the human genome, health professionals will be able to make dietary recommendations tailored to lower the risk for a specific disease in an individual. But before that can happen, we need to know more about the slight variations in specific genes that affect their interactions with other genes and with nutrients. Although the genome defines us as humans, it is these variations that define our individuality. They determine who we are in terms of blood type, skin color, physique and so on. They also determine an individual’s genetic risk for disease.
Researchers are now looking for the variations that increase susceptibility to common maladies such as heart disease, cancer and Alzheimer’s disease. As they become known, it will be possible to determine how they affect the genes’ interactions with nutrients. In a practical sense, this knowledge will greatly improve the ability to predict how an individual with a particular gene variation will respond to a dietary change and to choose rational dietary recommendations for reducing disease risk. Someday, a person whose physician has determined that he or she has a genetic susceptibility for a certain disease may consult a dietary counselor and find out what foods need to be eaten or avoided and what diet supplements may be needed to optimally reduce the risk for developing the disease.