Of all the books written on nutrition, none has been more popular than Dr. Peter D'Adamo's international bestseller, Eat Right 4 Your Type (ER4YT). With sales in excess of a million copies and translation into more than 40 languages, the book is a bona fide phenomenon. There are ER4YT cookbooks, diet cards, and supplements. There even is an organization called the International Foundation for Blood Type Living, whose sole mission is to promote the philosophies of EF4YT throughout the world!

As the name implies, ER4YT links nutrition to blood type. It puts forth the hypothesis that your blood type is a product of evolution and, because of the evolutionary process, impacts the way in which your body responds to various foods. Here is a brief synopsis: Type O's are the "original" blood type and consequently thrive on the high protein/low carbohydrate diets of cavemen; type A's descended from farmers (at or around 25,000 B.C.) so they respond best to high carb/low protein vegetarian diets; type B's trace their ancestry to nomads (emerging about 15,000 years ago) and should therefore eat a mixed diet; and Type AB's (evolving within the past 1000 years) are an amalgam of types A and B, allowing them the leeway to consume a combination of the two diets.

The basic premise of the diet revolves around little gremlins called lectins (a food-based protein) and their ability to cause agglutination (a reaction in which particles suspended in a liquid collect into clumps). According to D'Adamo, the lectins contained in certain foods cause a host of unwanted reactions in people who are not genetically suited to consume these foods; if you don't eat right for your type, bad things happen.

Alternatively, by eating in a manner that does coincide with your blood type, D'Adamo claims you can avoid the negative consequences of lectins and thereby enjoy a happier, healthier life. You'll maintain your ideal weight, elevate your energy levels, and stave off the aging process. In sum, by following the rules of blood type living, you'll magically change your life.

The truth is, however, there isn't a shred of evidence that supports the blood type diet. Despite its scientific posture, ER4YT is woefully short on substance. D'Adamo presents no peer-reviewed documentation to back up his exorbitant claims. None! He refers to his research throughout the book but does not list a single study he has published in a scientific journal. Instead, various scientific principles are taken out of context and twisted around to suit his fancy. This isn't science; it's pseudo-science, or worse, charlatanism.

Consider D'Adamo's assertion that, when a person with Type A blood eats meats or other high-protein sources, the lectins in these foods cause erythrocytes (red blood cells) to agglutinate (clump together). If true, this would have serious ramifications. Over time, the clumps of erythrocytes would become extremely large and clog up the body's vast network of capillaries (tiny blood vessels). This would impede blood flow and thereby prevent oxygen from being delivered to bodily tissues. Without a steady supply of oxygen, the vital organs would become irreparably damaged and, in short order, result in death. Pretty scary stuff!

But while this scenario certainly sounds ominous, there is nothing to show that it actually occurs in real life. A search of all available literature fails to reveal even one instance where food-induced agglutination of erythrocytes produced cardiovascular complications. If blood type really had such an effect on food, it would be common-knowledge throughout the medical community. Sophisticated medical tests such as Doppler ultrasonography would clearly show the dire consequences from agglutinated red blood cells in those afflicted. Yet none of this data exists.

D'Adamo's theory gets even more outrageous. He declares that, in addition to diet, blood type actually has an impact on your activity levels. Since type O's were hunters, they should engage in vigorous exercise; type A's, on the other hand, were docile agriculturalists and thus should engage in only gentle mind/body exercise. An incredible statement but again, where's the proof? By all accounts, there is nothing to show that people with type A blood have a decreased exercise response. Given the fact that moderate to intense exercise has clearly been shown to have a positive influence on longevity , these claims are more than just bad advice--they're downright irresponsible!

Even the anthropologic basis of blood types is highly questionable. Where has it been established that type O is the original blood type? The answer: nowhere. Cavemen didn't go around collecting blood samples. Blood typing didn't come about until 1901, when Austrian immunologist Karl Landsteiner identified the primary antigens and developed the accepted system of classification. Hence, it's a huge leap to assume that blood types evolved due to dietary concerns. Quite to the contrary, evidence seems to suggest that the ABO blood groups have been around since the dawn of man . In fact, the AB type (which D'Adamo says is the most recent blood group) apparently has a lineage that dates back more than 13 million years!

While there are those who claim to have achieved remarkable success by following the blood type diet, any benefits are likely accidental. For instance, approximately 10 percent of the population are lactose intolerant . Hence, there is a statistical probability that if a group of people with type O blood limited dairy products, some of them would benefit from the action. But this in no way indicates that there's a cause/effect relationship between type O blood and restricting dairy products. It's simply a reflection of the elements of chance; if enough people follow a given diet, some are bound to experience positive results.

In D'Adamo's own words, a theory is "a system of interrelated ideas, often based on one main principle, that can have many related hypotheses. If research confirms a lot of the related hypotheses, researchers may infer that the theory is basically sound. If research fails to support a lot of the related hypotheses, researchers need to reconsider the theory's worth." Well where is the research for blood type living? Based on these criteria, it's time to go back to the drawing board and come up with another theory!

In final analysis, ER4YT is nothing more than a lot of hype. Nutrition is an extremely complex subject. Factors such as activity levels, medical history and food allergies, amongst others, must be taken into account when devising a dietary strategy. Ignoring these important provisos can lead to a variety of complications, some of them potentially serious. Relegating nutrition to something as simplistic as blood type is beyond implausible-it's completely ludicrous.

To put things into perspective, your blood type shouldn't dictate your eating patterns any more than the interior of your car should determine which gasoline you put in it. Fad diets won't solve your nutritional problems; healthy eating will.