Food for Your Blood?

Last Editorial Review: 1/30/2005

Eating by blood type.

WebMD Feature

July 24, 2000 -- When Michelle Murdock and her husband sit down for dinner together, they never eat the same meal. While she doesn't eat meat, her husband eats it often. She loves peanut butter; he avoids it. She shies away from dairy products, while he consumes all the milk and cheese he wants. Why do their menus vary so widely? It's not because they have different tastes -- rather, they have different blood types. (Hers is type A; his is type B.)

The Murdocks follow the "Eat Right for Your Type" diet, which encourages people to consume certain foods and shun others based on their status of A, B, AB, or O. Michelle, 29, has been on the diet for almost two years and is still enthused. "I lost about 35 pounds the first year I was on it," she says. ''I have since maintained a healthy weight." She says she has the energy of a teenager.

Who'd think a diet would be based on blood type? The theory is the brainchild of Peter J. D'Adamo, ND, a naturopathic physician in Stamford, Conn., who touted the program in his 1996 book, Eat Right for Your Type, which gave the diet its name. Eating this way can not only keep you healthy and help you lose weight, D'Adamo says, but not eating this way can harm you, perhaps setting you up for digestive problems or serious ailments, including cancer. Not everyone agrees with D'Adamo -- the diet is roundly criticized by most mainstream nutritionists and medical doctors for the lack of published evidence showing it works.

But criticism is not enough to deter as many as two million people who follow the diet (the figure comes from D'Adamo and is based on visitors to his web site and his private practice). These blood-type diet fans don't mention feeling deprived because of food restrictions, but talk instead about how good they feel. Many, like the Murdocks, embrace the diet as a new lifestyle.

The Diet's Theory

One reason for these dieters' enthusiasm is that there's no counting of calories or fat grams. Instead, the diet emphasizes eating certain foods, in any quantity you'd like. For instance, Type O's are advised to eat meat but no grains. Type A's should be vegetarians. Type B's can eat the most varied diet, including meat and dairy products. And Type AB's should eat some meat, but lay off cured or smoked meats.

Why are certain foods specified for each blood type? D'Adamo believes that lectins, proteins found in foods, can wreak havoc in the body. If you eat a food containing lectins that are not compatible with your blood type, he says, the lectins can target an organ or system in the body. This can adversely affect blood cells in the area and possibly cause disease, including kidney disease and cancer. However, these negative effects can be avoided by focusing on foods that mesh with your blood type, D'Adamo says.

D'Adamo also theorizes that a person's ability to digest foods varies depending on blood type. For instance, he claims that Type O's can efficiently digest meats because they tend to have high levels of stomach acid. Type A's, he says, have low stomach acid and store meat as fat.

D'Adamo bases his theories on research he's conducted since the early 1990s on the connections among blood type, food, and disease. He says his research builds on work done by his father, a naturopathic physician who drew on his observations of his patients. Based on those observations, D'Adamo also suggests that type O's should exercise vigorously, B's moderately, and A's gently. AB's, he says, need calming exercise.

Where's the Beef?

While D'Adamo acknowledges that there is no scientific study that demonstrates that his program helps with weight loss or disease prevention, he has posted 52 pages of references on his web site ( that he says back up his belief that blood type may be related to disease. But many mainstream nutritionists and medical doctors roundly criticize the program and urge their patients not to follow it. These critics cite the lack of published studies showing that the diet works.

"My initial skepticism of the diet plan was supported by the complete lack of scientific foundation [in D'Adamo's book]," says John McMahon, ND, a naturopathic physician in Wilton, Conn. "I believe he feels he is doing people a favor, but I think he is seriously mistaken."

Adds John Foreyt, PhD, a weight loss researcher at the Baylor College of Medicine in Houston: "I know of no plausible rationale behind the diet."

Critics also quibble with D'Adamo's theory that there is an association between certain blood types and specific diseases (which he says can be tempered by eating certain foods). Though this theory has long been talked about and investigated, no conclusions have been reached, says Andrea Wiley, PhD, an associate professor of anthropology at James Madison University in Harrisonburg, Va. It would be a huge leap, she adds, to say with certainty that a person with a specific blood type will probably contract a specific disease -- as D'Adamo claims when justifying his diet.

Potential for Harm?

In fact, some experts go so far as to say the diet may be harmful. Michael Klaper, MD, a general practice physician in Pukalani, Hawaii, says eating large quantities of meat, for instance, is discouraged by most diet plans, because the fat can add up and it may leave you too full to eat other crucial foods. In another example, a lactose-intolerant Type B, who would be encouraged by D'Adamo's plan to eat a variety of dairy foods, would have significant difficulties, Klaper says.

One East Coast physician interviewed for this story (who didn't want to be quoted directly) says he has recently cared for three patients who were adversely affected after following the blood-type plan for a few months. One gained weight; another experienced joint pain. A third had an increase in blood cholesterol, from a respectable 183 to an undesirable level of 272 (over 200 is considered abnormal).

Even supporters of the diet say it is difficult to stay within its confines, given the long list of foods to avoid. For instance, the diet advocates that type B's forgo shrimp, pork, chicken, ice cream, American cheese, peanuts, black beans, granola, whole wheat bread, wild rice, and tomatoes, among many other foods. If family members have different blood types, following the diet can be even more difficult.

Not Proven, But Still Popular

Like many other scientists, Wiley is puzzled as to why the blood-type diet has gained such a following. "Dieting is one of those things people feel desperate about," she says. "The blood-type diet sounds more scientific [than some others]." And that, she says, could help explain why it has been embraced even by people who don't generally follow fad diets.

Michelle Murdock, for one, plans to stay on the blood-type diet for life. She has a strong family history of colon cancer, breast cancer, diabetes, and heart disease and hopes that following the diet -- despite the inconvenience -- will reduce her risk of developing these ailments. The few meals she, her husband, and daughter can eat together are sushi, some vegetable dishes, certain soups, and fish. "But we have gotten used to it," she says.

Kathleen Doheny is a Los Angeles journalist and a contributing editor for WebMD. She also writes for The Los Angeles Times, Shape, Modern Maturity, and Working Woman.

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