People with type O blood should eat high-protein diets with plenty of vegetables, lean meats, fish and poultry, according to WebMD. They should avoid eating legumes, grains and dairy.
The Blood Type Diet was created by Peter D'Adamo, a naturopath. He recommends diet and exercise choices based on an individual's blood type, stating that food and supplements interact differently depending on the blood type. People with type O blood have the oldest blood type, characterized by energy, leadership, extroversion and aggressiveness. A poor diet can cause people with type O blood to gain weight and develop insulin resistance, and it can harm their thyroid glands.
The Blood Type Diet is highly criticized for having very little scientific evidence to back up D'Adamo's claims, reports WebMD. While weight loss is possible due to the very restrictive nature of the diet, D'Adamo's advice does not take into account chronic health conditions, such as diabetes, that influence diet. The Blood Type Diet fails to address heart disease, high cholesterol and high blood pressure, though weight loss is believed to have a positive effect on these conditions. The Blood Type Diet is unable to support its claims that its recommendations lead to more energy and can help with digestion problems.