You can learn a lot from your blood -- cholesterol levels, genetics, liver function. And now some believe blood is the key to weight loss.
Everyone knows exercise and eating right can help you lose weight, but some say what runs in your veins determines which foods are best for your body.
Peter D'Adamo is naturopathic physician and author of the book "Eat Right for Your Type," a New York Times best-seller.
The book suggests limiting foods depending on your blood type.
For example, for those with Type O, he suggests a high-protein diet with meat, vegetables, and fruits. People with Type A do better on vegetarian diets that include soy proteins, grains, and veggies. For Type B, it's low-fat dairy, meat, and produce. And finally blood Type AB benefits from seafood, tofu, dairy, and produce.
Each of these recommendations also come with exercise guidelines for how vigorous or gently you should work out.
So the big question: Does it work?
"There is not a lot of science behind blood types determining the diet," said Baylor Dallas Dr. Roger Khetan.
Dr. Khetan sees several patients who use the blood type diet.
"I'm not thrilled with all the consequences of the book," he said. "It may work for some people, but I think there are some diets out there that will work better."
Dr. Khetan suggests eating smaller portions of healthy food more often, and, of course, exercising.
D'Adamo's diet is creating a lot of curiosity, even more than 15 years after first being published.