Synopsis behind the blood group diet:
Your blood group determines the way you absorb nutrients from the gut and how your body handles stress. This is postulated to therefore influence your health (in terms of disease) and weight. This diet is very restrictive as it recommends cutting out certain food groups. For instance, if you are type O = you are a meat eater, if you are type A = you are a vegetarian and type B = you are a dairy eater.
Is there any scientific evidence to substantiate this claim?
At this point (and from when D’Adamo first “designed” this diet) there has been no scientific research to back up this claim. This means that it has not been tested in any sort of way (not even on rats or mice, let alone humans) – the safety of this diet is therefore under question as well as the theory behind this diet. There is no literature in any database which backs up the theory that your blood affects the way you absorb nutrients – physiologically I don’t see how this is even possible.
For some people following the eating guidelines for their blood group may improve their general health and/ or decrease weight HOWEVER this is mostly likely due to an OVERALL DECREASE IN ENERGY INTAKE (which of course will anyway lead to weight loss – this will happen for anyone who reduces energy intake). So when this diet may work is for example: those who move from a diet which contains sources of medium fat meats and other fats (saturated fats = chips, biscuits, cakes etc.) to a diet which only contains only vegetables (vegetarian diet). This is however a radical change which most people will not be able to maintain… The other problem with the blood group diet is that it restricts or cuts out certain food groups therefore vitamin and nutrient deficiencies can occur. For example: vegetarians could become iron deficient and therefore suffer from anaemia as well as B12 deficiency. Those who don’t consume milk can suffer from osteoporosis later in life and those who only eat meat will have a low antioxidant intake, due to low intake of fruits and vegetables, which doesn’t necessary result in deficiency all of the time but the individual is most likely to have more sick days etc.
So, cutting out food groups completely is not the best idea.
Therefore, I would not recommend the blood group diet to anyone – I would also not suggest adapting it as there still may be some deficiencies that can creep in – I would therefore suggest should you have a certain plan in mind, it would be best to consult a nutrition expert = dietitian (please note registered nutritionists do not qualify with a degree therefore are not considered experts in nutrition). Dietitians have a unique ability to assess your diet for the adequacy of all nutrients – macro (carbohydrate, fat and protein content) as well and micro (vitamins (A, B1, B2, B3, B6, B12, folate and the list goes on) and minerals (Ca, Mg, P, Zn, Fe and the list goes on).
Should you feel you need some advice, visit a registered dietitian.