Diets effect different people differently. This is genetic. Tylenol effects different people differently. This is the same genetic issue. Does this mean that people would be better off trying to harness these differences by doing different types of diets based on their blood type? People who make money on it say yes. I say no. They aren't going to injure you, it's just useless to be incredibly complex when it doesn't matter. The rules of healthy nutrition apply to everyone regardless of blood type. Some people take heroin once and it kills them. Others do it for 20 years and only get the shakes. Heroin is bad regardless. And luckily, no heroin will be in your diet.
Now I'm obviously blowing it out of proportion a tad using heroin addiction as an analogy, but the underlying point is this: some people might be lactose intolerant. Others are diabetic or allergic to nuts. These things call for diet modifications, but this has very little to do with being type O negative or whatever you happen to be. I'm O negative, that's why I said that. And if I was any other blood type I wouldn't have to eat so much clam and natural salsa. That's a joke. Kind of. The main point is that blood type doesn't really dictate bioenergetics and ingestion.
When we take the genetic based dieting beyond blood typing, the science is promising. The promising parts have nothing to do with diet specifications though. Outside of the rules that apply to everyone, it's a genomic issue rather than caloric. Anyone who says otherwise has something for sale.
We'll look at some details. Some people have a genetic defense to blood pressure increases. Others don't. Genetic based dieting says those who don't shouldn't eat mass quantities of salt. And this advice is great, but it's kind of a general rule of healthy dieting for everyone. Lets look at another one, E4: a gene that makes smoking and drinking even worse for you. Bad gene. Eating less saturated fat makes it not as bad. So if you're a smoker and/or drinker, eat less saturated fat. Again, eating less saturated fat is a general rule for healthy dieting in everyone. Every human alive would benefit from not eating as much of it. So effectively what they're doing is taking the general, fundamental rules, and advising them in a more specific way. The only thing new about it is the level of confusion.
Most of the research on the subject, however, addresses obesity, being as that's what's marketable. And there exist over 300 genes that impact it. That's about the extent of what we know. We don't really know how to deal with the genes in a way that will solve anything yet. Obviously if we did, we wouldn't all be huge. But conducting further research on drug interactions with those genes is good I think. Capitalizing on people's insecurity and trust in science to sell useless shit to a fat human being is less good I think.
Either way, drug intervention and amount of pork in your diet are two very distinct things. Once of which might genomically assist obese people in the relatively not-near-at-all future, while the other bears no resemblance to genetic anything. I assume you can guess which is which.
Regarding genetic based supplement products, consider this: the research on genetic therapy is not cheap. It is conducted to make not-cheap, patented drugs based on the findings. Cheap supplements bear little resemblance to this, and will therefore offer you 0% assistance to your goals.
So the overall validity of genetic based dieting: none. The validity of genetic drug therapy: in the future it will be hugely effective and still have nothing to do with your diet. I can't say the knowledge of diet won't ever coincide with genes in the future, but we would have to learn a lot more about genes, and then invent some new foods with effects of drugs. And I don't predict that will happen soon. So stick to your standard principals for now.