Diet, particularly in relation to autism spectrum and related conditions, has been of some interest to me for many years in terms of what is eaten, what effects dietary components may have both physical and mental, and the various views on what 'should' be eaten in order to maintain good 'get-through-the-day health'. The more I read about diet in general and what we should or should not be eating, the more I paradoxically become both informed and confused. I say paradoxically because there are a quite bewildering array of schools of thought on what is the right kind of diet and the various evidence to corroborate (or not) such views.
Yes, I hear you cry, 'we are all different in terms of our genes and environment', and this perhaps is one of the more important points relating to what our diet should be composed of. We know for example that different populations are at different general risk of different issues related to food. With sweeping generalisation, for the South-East Asian populations, the problem is with milk (or rather the enzymes used to break down the sugars in milk). For the Northern Europeans it is gluten (and the elevated risk of coeliac disease amongst those of Irish descent). Without wishing to simplify such associations, it appears that such problems are either a result of evolutionary mechanisms (i.e. what foods different populations have been exposed to) and/or biological mechanisms (i.e. what mechanisms exist to process different types of foods). Taking this latter issue in particular, on different bodies reacting to different foods as a function of underlying genes and biological mechanisms, one of the interesting areas potentially pertaining to this is the issue of blood type.
'Eat right for your blood type' is the message from the main protagonist Peter D'Adamo. I would perhaps state quite categorically here that I am in no way advocating this or any other dietary method; merely describing and discussing (to coin a phrase from my undergraduate days). D'Adamo is a naturopathic doctor who has been involved in this area for quite a few years. I don't know a lot about naturopathy so you will perhaps have to excuse my ignorance and use this link as a description. The primary message from the eat right/blood type school of thought is that the ABO blood typing nomenclature might be a roadmap towards which kind of foods are 'right for you' in terms of promoting health (and disease) as a consequence of the relationship between things like dietary lectins and blood type. I am not going to do into the details about what foods might or might not be right for each blood group because it would take too long and turn this entry into some kind of dietary advert (for which I am neither qualified nor inclined to do so).
I had to think about the main thrust of this theory for quite a while before writing this post. I am slightly torn between thinking there could be something in this school of thought and the various 'issues' that I have with it. The main issue relates to the lack of scientific literature around this suggestion. I have for example, yet to find that big paper which has looked at different diets and different blood types under RCT conditions. If anyone can point me in the direction of such studies, I would be grateful. Having said that in my own area of work looking at the possibility that a gluten- and casein-free diet might be 'helpful' for some people with autism, there is a similar dearth of controlled trials reporting an effect!
The part of the diet/blood type theory that I am drawn to relates to the evolutionary perspective and D'Adamo's description of different evolutionary factors impacting on health, possibly as a consequence of things like blood type. I have said it before but Emily Deans over at Evolutionary Psychiatry talks quite a lot about the Paleo diet (and Paleo 2.0) and how, whether we see it now or not, humankind was until quite recently not raised on things like bread, milk and other components of the modern diet. Reading her various posts, and that of her contributors, they make a strong case for such a dietary effect. Indeed, the evolutionary perspective ties into quite a lot of research for example suggesting that our distant ancestral relations enjoyed a life of fruit, nuts, seeds, and the odd bit of fish or mammal (provided you could catch it). That combined with eating by season, living by the sea and having to actually find and kill your prey in the sunlight rather than popping into the car to go the half a mile or so to the supermarket for it, makes for some interesting comparisons with modern life and perhaps modern patterns of disease. The evidence for this more 'traditional' diet is quite plentiful and has been covered, quite unwittingly, in some of the other posts on this blog in relation to things like ADHD.
I would perhaps criticise the blood type/diet the same way I would criticise any diet in the assumption it makes about people all being the same. I don't know my blood type, but even if I did, I assume that my genetic make-up based on my family history presumably of mixed blood types down the centuries and my subsequent exposure to all the stresses of modern life, would make me individually susceptible to foods and health problems which even someone sharing my blood group may not have such issues with. The other issue I have is the basis for blood classification and the ABO and rhesus systems. There are other, not so common ways, of categorising blood type, which currently number about 30. I do perhaps wonder if some of these categorisations, used alone or in conjunction with the ABO rhesus system, may actually provide a more accurate reflection of how our genes might determine our relationship with nourishment from our environment.
Food for thought?