So apparently there's an entire field called Nutrigenomics, which is "the study of molecular relationships between nutrition and the response of genes, with the aim of extrapolating how such subtle changes can affect human health." This is ****ing cool. The idea is that with a simple DNA test one can determine how they will react to consuming different amounts of substances, such as carbs, fats, proteins, creatine, caffeine, cholesterol, etc. From this you can eliminate the guess work in figuring out what type of diet will help you achieve your goals.
Here is an interview with a pioneer in the field.
And here is the Wikipedia entry.
This has the potential to be very awesome.