The blood type diet was invented in the late 1990s by a man called Peter d'Adamo. His main principle was that human beings have evolved over time and that our diets have adapted to suit our blood types.
What should type Os eat?
According to d'Adamo, people who have type O blood (the majority) should do an awful lot of exercise and eat plenty of red meat. Fruit and vegetables are okay, but carriers should cut down on dairy and grain foods.
And type As?
People with blood type A should try and cut down on meats and tend towards a more vegetarian diet but they can also eat a little fish and chicken from time to time. The diet suggests that type As may gain significant benefit from eating soy and pineapple products.
Type Bs can supposedly eat anything in moderation, but with a few notable exceptions such as peanuts and chicken (chicken satay must be off the menu), while type ABs should avoid red meat but will enjoy pineapple, soy, greens etc.
Does the diet work?
The diet will probably work in as much as watching what you eat will have more effect on your weight than scoffing two Big Macs and a large fries will. But there cannot be any scientific rationale behind isolating whole or partial food groups from your diet, and in fact it could be putting you in danger of nutritional deficiencies.
Fundamentally, the diet may make you thin but it won't necessarily make you healthy the best thing to do is to stick to a sound, healthy diet with moderate exercise each day. The blood type diet will appeal to those who want to slim down through a quick fix: genetics plays a part in your build, but so do sensible eating and physical activity.