Blood type diet plan - a critical review part II

In Part I of this article on the blood type diet plan, I mention that it appears scientific because it employs blood tests to determine the foods we should eat as well as those we should avoid.

Yet the main criticism of this diet is that it is NOT scientific. Dr Peter D'Adamo, a naturopath, claimed he developed the blood type diet based on more than 15 years of scientific research.

None of his "research" has so far been replicated by other scientists, meaning no one else has been able to confirm that what Dr Peter D'Adamo claims is, in fact, true.

At the same time, many of the assertions by Dr Peter D'Adamo are being challenged by other scientists as being either inaccurate, or untrue.

Evolution of blood types

A key assertion to justify the blood type diet plan is the evolution of blood types. According to Dr Peter D'Adamo's hypothesis, Blood Type O was the first to appear. It represents the blood type of early hunter-gatherers and so people with Blood type O should eat a hunter-gatherer type of diet with plenty of meat.

Next came blood type A, about 20,000 years ago, which represents the blood type of farmers who settled down in communities and planted crops. People with Blood type A should be more vegetarian.

Then came Blood type B, about 10,000 years ago, which represents farmers moving out of their communities. People with blood type be can therefore eat more varied diets comprising meat, vegetables and dairy products.

Finally came Blood type AB, about 1,000 years ago, which represents the transition to modern times. People with blood type AB can therefore eat even more varied diets, combining the diets of both Blood types A and B.

This is the rough explanation for the blood type diet. But was it really what happened? Many scientists challenge this and they have reasons to believe that Blood types A and B arose long before Blood type O, not after.

The reasons for this belief are complex but put simply, they have to do with genetic coding. The genetic codes for Blood type A are the most ancient, dating back around 6.5 million years, followed by the codes for blood type B, which date back around 3.5 million years. Then came the genetic codes for Blood type O, which arose around 2.5 million years ago.

Moreover, Blood type O has a gene that is considered "faulty" and it is highly unlikely that a faulty gene could subsequently evolve into normal genes in blood types A and B.

Lectins and blood clumping

Another key idea used to support the blood type diet involves lectins, which are protein molecules that bind with sugar.

Scientifically, it is known and accepted that certain foods - such as beans, grains, seeds and nuts - have high concentrations and that such foods can be harmful if consumed in excess, especially if they are not properly cooked. Among other things, such foods may cause allergic reactions or nutritional deficiencies.

Dr Peter D'Adamo, however, goes further in justifying his blood type diet. He claims that if a person eats foods that are unsuitable for his / her blood type, the lectins in these foods will make blood cells clump together - in a process called agglutination.

This is very serious. Wnen blood cells clump together, blood cannot flow through fine capillaries to do their jobs of delivering oxygen and nutrients to cells and organs. It means the cells and organs will eventually die. Going by the blood type diet hypothesis, people have very high chances of eating the "wrong foods" and, as a result, suffering from blood agglutination all the time.

Dr Peter D'Adamo says that blood agglutination is "visible under the microscope" but critics counter that what happens on a glass slide under a microscope is not the same as what happens inside the body - because the environment of the intestines is different.

Also, the human body has antibodies that counter the effects of lectins present in foods such as soy, wheat and peanut. The protective effects of these antibodies cannot be observed under a microscope.

Critics further point out that Dr Peter D'Adamo has not demonstrated that organ damage actualaly occurs due to blood agglutination from not following the blood type diet. Nor has he cited scientific references about such damage.

Blood types and bacteria

Another claim by Dr Peter D'Adamo to support his blood type diet concerns how foods interact with bacteria and mucous secretions in the intestines. This can be determined by a urine test - called the urine indican test - to measure the level of certain chemicals called polyamines. Basically, high levels of polyamines indicate various problems in the intestines, such as inflammatory bowel disease, celiac disease, gastric ulcer, diverticulosis, etc.

According to Dr Peter D'Aamo, the urine indican test shows that when a person eats the "wrong foods", the effects of carcinogens (cancer causing substances) are "magnified 90 times".

Again, critics of the blood type diet point out that there is no scientific evidence to support this claim. Instead, there is scientific evidence that the body secretes enzymes that can repair damage caused by lectins.

Blood types and digestion

The blood type diet is also based on apparent differences in the amount of digestive juices - including stomach acids and enzymes - secreted by people of different blood types. Dr Peter D'Adamo claims, for example, that Blood Type O secretes higher levels of stomach acids and this is why such people should eat more meat.

It is true that people of Blood Type O tend to have higher incidents of peptic ulcer of the duodenum and Dr Peter D'Adamo cites this as "proof" that they secrete more stomach acids. But it is not true that ALL Blood type O people secrete higher than normal levels of stomach acids, only some do. Moreover, peptic ulcers in the duodenum are not due solely to stomach acids. These ulcers tend to be localised whereas if stomach acids were the main cause, the ulcers would be widespread.

Critics of the blood type diet further note that protein is not digested by stomach acid, but by pepsin. What the hydrochloric acid in the stomach does is convert pepsinogen, which is inactive, into pepsin, which is active. But... an optimal level of stomach acid (ph 2.0) is needed for this. When the stomach is overly acidic, pepsin becomes less effective in digesting protein. So it is not true that people with high levels of stomach acids should eat more meat and protein. They do not necessarily digest such foods better.

There are lots more criticisms of the blood type diet. While Dr Peter D'Adamo tries to present the blood type diet as being scientifically-based, many of his claims are, in fact, not supported by science. Some critics even call his diet plan "blood type astrology."

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