> it is really impossible to completely test the theory scientifically.
This shows a misunderstanding of what science is about. You can set up control groups, that use different eating methods, but consuming the same amount of calories (and micro nutrients, etc.) over a given period of time. In some settings, double-blind experiments (with placebos) are indeed "better"; but it is not required to get scientifically valid results.
True, I may have over stated my point. A double blind with placebos test is the gold standard, and difficult to implement with humans when it comes to diets. Which is why I think there are so many different kinds of fad diets that come and go, which is sort of the point I was driving at. It is just really difficult to conclusively prove.
I think the main problem is that people are looking for some kind of silver bullet diet that will make them healthy and live long. So, since there's demand, there are other people providing them with it.
Of course it's just air, there's no such thing as a silver bullet diet. Health and longevity depends on so much more than just diet that there will never be such a thing.
But still, since there's money to be made by selling dummies miracle diets, there are some to sell. And since they can't sell the real thing because it can't be made, they do what they can to convince the customers that it is. Among other marketing tricks, pervert science so it looks like their snake oil is based on something more than just the will to make money from gullible people.
There might be some good science in the nutrition field. Sadly, it's drowned in a sea of wishful thinking, bad science and plain charlatanry...
This shows a misunderstanding of what science is about. You can set up control groups, that use different eating methods, but consuming the same amount of calories (and micro nutrients, etc.) over a given period of time. In some settings, double-blind experiments (with placebos) are indeed "better"; but it is not required to get scientifically valid results.