— Barbara Romuld, Winnipeg, Manitoba
A: The premise of this plan is that your blood type indicates the prehistoric group you're descended from, and it reveals what your digestive system can tolerate. Type O, the oldest blood type genetically speaking, supposedly indicates a need to eat meat every day because the earliest populations were hunter-gatherers. People with type A are descended from agrarian cultures and, the theory goes, should follow a vegetarian diet.
If that sounds a little wacky, it is—although blood type does have some influence on health. Researchershave known for years that type Os tend to be more susceptible to ulcers, for example. And food allergies or intolerances may be related to blood type.
But following this diet to the letter could deprive you of essential nutrients. Dairy and grains are pretty much off-limits for Os—the most common blood type. I probably don't need to remind you that the calcium found in dairy is essential for healthy bones and that the fiber in whole grains can protect your heart.
In addition, the idea that we have the exact same dietary needs as ancestors who walked the savannas in 50,000 B.C. is extremely far-fetched, and helps explain why most respected medical experts do not support this approach. Worry about your blood type when you need a transfusion, not a meal.
David L. Katz, MD, is director of the Yale-Griffin Prevention Research Center and president of the nonprofit Turn the Tide Foundation.