One basic form of nutrigenomic diet has long been in existence, creating pretty radical changes in diet (albeit by default).
When it comes to gluten intolerance or lactose intolerance, some individuals' genetic makeup prevents their ability to process wheat or dairy products. You don't need a DNA test to find this out, as your body will express its displeasure upon coming into digestive contact with these substances. Food intolerance makes people feel ill when they've chosen the wrong menu item, but many people don't realize the nature of the problem until after consulting with a doctor.
While avoidance of non-tolerated foods solves the problem, supplemental enzymes can also be consumed that allow for the consumption of these products. But do some people develop food intolerances while others don't? The root of the problem is genetics.
We'll take lactose intolerance as an example. Humans -- like animals -- traditionally have lost the tolerance for lactose by the time of adulthood. However, people in Northern Europe about 10,000 years ago developed the ability to continue tolerating lactose through adulthood. Descendents of those Northern Europeans are much more likely to be free of lactose intolerance than other ethnicities. But if your ancestors made their home in Asia, Africa or even southern Europe, that's not a definite indication you won't be able to drink a glass of milk as an adult. Future nutrigenomic testing may be able to determine beforehand if you'll develop a food intolerance, and may even be able to suppress or facilitate the expression of certain genes that can prevent this from happening.
As the study and practice of nutrigenomics advances, it will undoubtedly yield surprising dietary insights and personalized benefits to those who pursue its offerings. And by altering your diet to better suit your genes, your genes may allow your diet to better suit your jeans.