To Your Health

What is the rationale for the blood type diet for weight loss?

Q. What is the rationale for the blood type diet for weight loss?

A. About 10 years ago the "blood type" diet was made popular by a book written by Peter J. D'Adamo, N.D., Eat Right for Your Type. In it D'Adamo asserts that an individual's blood type (O, A, B, or AB) determines how our bodies deal with different foods and that eating foods that are not matched to your blood type leads to all sorts of health problems, including weight gain. He believes that when your diet is not matched to your blood type, lectins, which are proteins found in certain foods, can cause damaging blood clots to develop that over time reduce the blood supply to vital organs. In addition, he believes that there are differences in the digestive processes of individuals with different blood types and that their gut bacteria are different. Coupling these differences with his ideas on the kind of diet our ancestors were eating at the time in history that each blood group appeared, D'Adamo devised detailed dietary regimes for each blood group.

From the first, the book was criticized for its claim to be based on science despite a lack of solid documentation. Scientists found a number of factual errors and also found fault with his broad speculations and assumptions. Nevertheless, many people claimed to be helped by the recommendations, and not just with weight loss.

You might wonder how the diet could work if the premise is flawed. One explanation is that implicit in almost every named diet is a restriction of either the amount or kind of food allowed. An often-unintended result is that "convenience" foods are restricted or even completely eliminated. A corn-free diet, for instance, will exclude most prepared and restaurant foods, forcing the dieter to return to home cooking that is often much more nutritious. Another factor is that a significant portion of the American population is intolerant of certain common foods without knowing it. Studies indicate that about 15% of the population, regardless of blood type, is "gluten sensitive" and would benefit from elimination of wheat. Even more, close to 25%, are lactose intolerant and suffer when they consume milk products. D'Adamo's diets sometimes eliminate whole food groups, and as a result the people who are bothered by these common foods credit their improvement to his diet.

While a connection between blood type and weight loss may be iffy, it is well-documented that blood type affects resistance to infection from certain germs. Many germs have markers that look like our blood types, and these markers will give them some protection from attack by our immune system. As a classic example, the germ that causes the Black Plague that swept through Europe eight centuries ago has a preference for people with blood type O. As a result, more people with blood type A survived and repopulated the area. Under more normal conditions, people with blood type O are more resistant to parasites, and when the Black Plague is not around they have the survival advantage. Scientists are aware of several such relationships with other diseases such as malaria and stomach ulcers.

The food we eat, even from infancy, will certainly influence our health, but rather than four diets for four blood types, there are at least 276 combinations of known blood antigens that you might want to investigate.

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