Peter D’Adamo believes that most of our food sensitivities are blood type specific. For example, people with blood type A are sensitive to lima beans, while other blood types are unaffected. Indeed lima bean lectin is so specific for blood type A that it has been used to type blood.
This makes sense, but I believe the majority of food sensitivities are idiosyncratic while the minority are blood type specific.
Why person-specific food sensitivities? Because our genes are unique (we have one gene for our blood type antigen and many genes for person-specific antigens) and our microbiota are unique, and some or most of the food sensitivities are due to disturbing various species in the microbiome (more precisely to altering key ratios of the various species). For example, suppose a type A person has an enteric yeast infection. Then, while grapes have no lectin known to irritate and inflame the type A digestive tract, and are allowed on the type A diet, yeast growth will be stimulated by one of ITS favorite foods, the grape. Also, when the person eats bread products, which are encouraged on the type A diet, he is overfeeding the yeast. Indeed any starchy (after breakdown) or sugary food (with the possible exception of milk, which has lactose) will overstimulate yeast and lead to problems.
Suppose a person of type A blood has a Helicobacter infection and the bacteria have acquired virulence genes. Whenever one stimulates acid production, one will irritate Helicobacter and Helicobacter will respond virulently. So in this case – consumption of too much coffee, which is allowed on the type A diet, or too much wine, which is also allowed, consumption of a very acidified 24 hour yogurt culture, but not milk (which buffers excess acidity), and of course whenever the person goes a long time without eating anything, and whenever person is under psychogenic stress, the acid pumps go into overdrive and irritate Helicobacter.