Why do cholesterol-rich foods cause blood cholesterol to rise only in some people? Why does a salty diet raise blood pressure in some, but not in others? Why does a high-carbohydrate diet help some people stay thin and healthy, while it causes others to gain weight and develop high blood triglycerides? Genetic factors play a major role—and scientists are gaining insights into how and why.
This field of research is called nutritional genomics (or nutrigenomics or nutrigenetics). Its goal is to devise nutritional guidelines based on genetic information in order to prevent, delay, or treat disorders such as type 2 diabetes, cardiovascular disease, obesity, and perhaps even cancer. Scientists are trying to develop genetic tests that would help determine which foods or nutrients you should eat or avoid to reduce your special risks.
For instance, a large Harvard study in the journal BMJsuggested that when people with certain genetic variants eat lots of fried foods, they gain more weight than those without the variants. And some small studies have found that people with a certain genetic profile need higher-than-normal intakes of folate (a B vitamin) and that this may affect their risk of cancer or heart disease.
In 2013, in a follow-up to a major clinical trial on the Mediterranean diet published in Diabetes Care, researchers identified a clear gene-diet interaction. In people with two copies of a genetic variant strongly associated with type 2 diabetes, the Mediterranean diet reduced the risk of stroke to the same level as that of people with one or no copies of the variant. In the control group, who ate a diet that was less Mediterranean, those with two copies of the variant were almost three times more likely to have a stroke. Adherence to the Mediterranean diet also helped counter the adverse effect of having two copies of the gene variant on levels of blood sugar, blood pressure, blood cholesterol, and triglycerides.
For now, nutrigenomics is in its infancy and much remains to be learned. Genetic profiles may reveal significant associations with various risks in large population studies, but so far have poor predictive value for any given person. Some day, however, it may be possible to have your genes analyzed to determine the optimal diet just for you.