Diet for blood type “0”. Dietitian's assessment: it just happened that, basing on the diet's author's suggestions for those with blood type “0” (i.e. basing on the pointed products and eliminating the undesirable ones) you are able to obtain menu rich in meat and poor in grains, what is really possible to support the process of losing weight. The author also advises to depend the final calorific content of the diet on the demand of a particular individual, which is quite right.
Unfortunately, the whole idea of diet based on the blood type is very controversial – it has no justification in science. The author of this diet makes many basic mistakes in his books, he ignores the knowledge of evolution biology or human physiology. There are many recommended products, that are not available or strange, which makes following such diet very troublesome.
To sum up: this kind of diet may (but it definitely doesn't have to) cause some results in a form of body fat reduction. The determining factor is the calorific balance, not the fact of assigning particular foodstuffs to those with blood type “0”. You can easily assume that the result would be similar (or none) in case of people with other blood types.
Diet for blood type “B”
Dietitian's assessment: when basing on the diet's author's recommendations for those with blood type “B”, i.e. excluding the inadvisable products and consuming only those foodstuffs which were presented as advantageous, it would be quite easy to obtain balanced diet, which provides high supply of all necessary nutrients. Therefore, it's not dangerous for health and it can be easily used by anyone. It also does not set an extremely low calorific supply, which in an advantage, compared to some starvation diets.
However, the concept of connecting the diet with blood type seems to be interesting, even though it has no scientific justification. The author's theory stating that blood type “B” occurred 15 thousand years before Christ in the Himalaya mountains is also peculiar. And that would be it for the formal criticism. If it comes to practice, this diet is needlessly fanciful, and some recommended products are quite expensive or unavailable. There are also no reasons to think that excluding from diet vegetables, such as avocado, mung bean sprouts, radish sprouts, olives, tomatoes, or exchanging pork with rabbit meat, would bring any results in a form of body fat reduction.
To sum up: if you feel that you are convinced with this pseudoscientific theory concerning the connection of blood type and proper nutrition, you can try it out. This diet is not dangerous for health, neither does it create the possibility of insufficiency (at least in its theoretical assumptions). The leaning potential of this diet does not result from the suggested choice of food – therefore, without any calorific restrictions, there will probably be no losses in body mass.
Diet for blood type “A”
The dietitian's assessment: the menu is rich in low-processed grain products, the author suggests limiting the intake of meat, including protein of plant origin and increasing the intake of fish – this diet seems to follow the current nutrition recommendations. Only one suggestion, i.e. limiting the amount of wheat, is quite interesting.
Just like in case of diets suggested for other blood types, in this case there is also no scientific justification. What's more, the author's suggestions are contrary to those from the science world and, therefore, undermine his credibility. Significant limit of meat (also totally excluding beef) and dairy products in diet may lead to insufficiency (of calcium, iron, vitamins from group B) in case of some people. Too high supply of unprocessed foodstuffs of grain origin, especially with higher intake of legumes, may lead to various digestion problems and make it harder to absorb some nutrients.
To sum up: individualisation of nutrition recommendations on the basis of blood type is unjustified. In case of a popular western diet, the diet for blood type “A” may turn out to be a better solution. For sure, it's far from perfection. This diet is rich in fibre and poor in sweets, fast food and other junk of that kind, so it may support body mass reduction. However, the loss of weight is more dependent on the possible calorific deficit than on the choice of food suggested by the author.
Diet for blood type “AB”
Dietitian's assessment: out of all “diets for blood types”, this one seems to be most “life-related”. According to the author, those with blood type “AB” may eat the products allowed in diets for blood type “A” and “B”. In fact, it's possible to compose a balanced menu basing on the list of advisable/inadvisable products without the risk of nutrition insufficiency. Diet for particular blood type has one advantage – it assumes eliminating highly-processed foodstuffs from the menu.
The disadvantage is, obviously, the scientific base, or rather lack of it. There is nothing, that would justify the claims of the author, which concern the correlation of diet and blood type. His conviction, according to which blood type “AB” occurred only more than a thousand years ago, is not so serious or inline with the current knowledge about evolution. When we agree that there is no dependency between blood type and nutrition, eliminating many products seems unjustified, both in the context of body fat reduction and improvement of health.
To sum up: it is the nutrition model for the enthusiasts of “alternative” to the current knowledge theories. As a dietitian, I cannot say that this diet is somehow threatening for health, although, total elimination of beef, pepper or avocado is just an unnecessary impoverishment of the menu. The diet has no slimming potential, unless there is some calorific deficit.