The human population is seldom either emotional or rational, but rather a mix of the two extremes. If we could truly measure this characteristic, what would we find?
I expect we would find something that looks like a normal distribution folded in half. A few high emotional, and a few high rational, and most of us in the middle.
What difference does this make? Well, if we were rationally driven, we could follow a diet without issue. But we cannot, therefore we are emotionally driven, when we fail. Add physiological in with the emotional, and we are in good shape. The model behaves as people.
Now the problem is that it is rational to set up a diet, and then say those that are unable to follow it have a philosophical, psychological, or physiological problem, but never accepting the issue that 50% of the people are not predominantly rational. So the diet industry is based on a non-understanding of people, so the failure rate will be high. Yes, exactly as we see.
Now how does one get hold of directing the emotional part of oneself? Adopt a god is one method. Adopt a philosophy, and convince the emotional part that it should be followed. Not so easy.
But we can also lever off our beliefs, bend behavior. Some things are just not food works. But that alone may not be enough. Perhaps we need a purpose bigger than ourselves, that we become obsessed with, regardless of what that purpose is. Perhaps it is understanding this disease, and understanding a solution, and describing that solution without resorting to a god for a solution.
Each time we go through this model, more is added, or refined. sooner or later it will all become clear. As we age, we may become more rational as well; hence, age out of the problem.
I think that we are reluctant to admit that we are emotionally based and are unable to consistently and committedly able to follow a rational plan of eating, aka a diet. We cannot be rational and still hang on to religion, so as long as we have religion, emotional govern people. This is beyond the issues of setting up and measuring food energy in a useful way.