As many genes as we have, some are surprisingly important when it comes to dietary interaction.
Researchers have discovered one gene that determines how quickly caffeine can be processed by your body. This decides how much caffeine can be tolerated by the body or how much a person may be likely to drink (especially if caffeine's effects fade quickly). It might not seem too important, but people who don't process caffeine as fast may be at higher risk of heart attack even if they drink less of it, according to Genome BC.
Speaking of heart health, genes make a difference in whether or not you'll improve your cardiovascular health through diet and lifestyle changes alone, or if improvement will require medication. The genetic makeup of some people allows them to eat pretty much whatever they want without raising their cholesterol levels. Other people can eat an extremely "cholesterol-smart" diet and their numbers won't budge at all. Knowing how your genes affect your dietary cholesterol intake will allow you to better tailor your overall approach to fighting high cholesterol -- or allow you to breathe easy and order an extra egg.
Researchers are trying to figure out exactly what foods in what amounts are optimal to prevent such diseases. It's known that calcium intake early in life reduces the risk and the speed of advancement of osteoporosis, but further nutrigenomic research should help us determine who needs calcium the most, and in what amounts.