Following up on my "failed predictions" point, I point at the now widely-distributed article about the low-fat vs. low-carb diets.
The standard dietary orthodoxy predicts that the results of this study would be exactly the opposite of what happened. The predictions are wrong. Therefore, the standard model is wrong. I don't need to be a nutritionist to make this determination.
I don't know what the right model is. I think that's pretty sad, considering that if nutritionists hadn't gotten bogged down by a premature orthodoxy, we would probably be now in the position of refining a solid idea, instead of where we really are now, which is quite nearly square one.