Eating to live longer: It can be a page turner

Some of Sears' claims are supported by clinical trials. When patients with Type 2 diabetes go on Zone-like diets, for example, their blood sugar and blood lipid levels have fallen. But a good fraction of the claims are theoretical. Nutrition experts have criticized Sears' basic premise -- that diet can control such a broad spectrum of hormones. And some finer details don't hold up to scientific scrutiny. There's no proof, for example, that the Zone Diet can improve skin tone by promoting collagen synthesis. And though it's true that consuming fewer calories can prolong life in various animals, the effect has yet to be demonstrated in people.

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Aging Fight It With the Blood Type Diet

Peter D'Adamo

Berkley Books, 2005

Naturopath Peter D'Adamo's first bestseller, "Eat Right 4 Your Type" (1996) introduced the idea that a person's blood type determines his or her dietary needs. In "Aging: Fight It with the Blood Type Diet," D'Adamo tailors the diet for those who want to stay physically healthy and mentally sharp into their old age.

The blood-type diet is based on the notion that people with different blood types share physiological characteristics: People of type O are purportedly prone to inflammatory diseases, whereas people of type A are deemed prone to free radical damage. Diets are prescribed based on these supposed vulnerabilities.

But first and foremost, each type's dietary recommendations are based on D'Adamo's theory that people should eat foods containing proteins that match the shape of the antigens, or proteins, on their blood cells. The details of this theory aren't replicated in the book (D'Adamo refers to his earlier works), but people with type O are advised to eat a high protein diet, those with type A to eat vegetarian, type Bs to avoid chicken and corn, and type ABs to eat a mix of meats and vegetables.

D'Adamo recommends four more approaches: consuming "brain foods" and probiotics, taking supplements and exercising -- all, again, based on blood type. Blood type B's top "brain power super food" is lean, organic, grass-fed red meat; type A's is the walnut. Aerobic exercise and weight lifting are recommended for type Os, yoga and tai chi for type As. The bulk of D'Adamo's book consists of tables and charts listing foods, supplements and exercises for each type, and ones to avoid.

Conspicuously absent from the book is an equally exhaustive list of sources or references to buttress his theories. He cites a handful of studies to make the claim that diet, exercise and lifestyle can keep brain and body healthy. But as he moves into the chapters detailing plans for each type, scientific references are slim.

Some research has linked blood type to susceptibility to diseases such as cholera, smallpox and malaria. But to date, there's no good evidence that tailoring diet to blood type can prevent disease, or prolong health into old age.

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