SAN ANTONIO -- There are plenty of diets, trendy workouts and modern procedures aimed at helping people slim down. One dieting theory takes a skin deep -- or vein deep -- look at weight loss.
Dr. Peter D'Adamo popularized choosing diets based off an individuals blood type in his book 'Eat Right 4 Your Type.'
The book suggests that people should look at their blood type and follow the dietary guidelines of their ancestors.
For instance, type O is the most popular blood type. It is believed to have first been born 30,000 years ago. According to the diet, type O people are hunters and should follow a high-protein diet -- like a caveman diet.
Type A blood people are cultivators, according to the diet. Therefore, anybody with type A blood should eat mostly vegetables.
The theory is believable, but critics say the diet lacks evidence and clinical trials.
"This diet seems pretty restricted in a few parts," a dietitian at the University of Texas Health and Science Center said. "I see it as a short term weight loss."
As a national best seller, D'Adamo's book sparked a lot of curiosity, and has people poking around to find out their blood type.