Actually, not so much. If you cherry pick resources,you can make this seem true, but if you broaden your (re)search (across time and place, to other eras and other countries and cultures) you'll find that over the decades, centuries, and even millenia, there have been a great number of theories as to how best to control body weight (whether one wanted to lose or gain depending on which was fashionable at the time) and likewise which foods promoted good health.
You don't even have to look back in time, even just today, if you look to other cultures, there's an incredible amount of variation in both the science and in what is considered "common knowledge."
Even limiting your studies to scientific and pseudo-scientific research of the last 150 years, you will find a great deal of conflicting data and conclusions drawn from the data.
As of yet, there's no unified theory (and little effort to create one) that would account for the wide disparity in research results. Instead you have theorists and their supporters trying to poke holes in the theories and research of other camps, each "side" dismissing, finding fault with, and/or ignoring any evidence that doesn't support their own theory.
Unfortunately, a unified theory isn't likely to be presented any time soon, maybe because there isn't one best answer. Maybe there is no one-type-suits-all diet. Maybe our genetics, age, health-history, health goals, lifestyle factors... all determine which diet or diets might work best for certain individuals and groups.
Personally, at this point in my life, I find myself leaning towards lowish carb and slowish carb paleo for myself (by slowish, I mean low glycemic), but not because I think everyone needs to eat this way, but because I seem to.
There might be other ways I could eat for health and weight loss, and there's CERTAINLY other ways that other people can (and do) eat for health and weight loss. There's at least as much compelling research support for low to moderate fat, plant-based diets as there is for high-fat, meat-based diets (The China study comes to mind). In fact, there's probably more, just because in many parts of the world, meat and even protein is and has always been relatively difficult to come by (other than by way of insects).
There's been some interesting research recently that suggests that a high-veggie, low-fat, moderate grain diet may be healthiest to prevent certain diseases, but that a high-protein, low-carb diet may be best to treat those same diseases.
I think we're finally starting to ask better (or at least more complex) questions - not, only "which is the best diet for health and weight control?" but rather, "which is the best diet for whom and for what specific health goals?"
Until then, I think it's important to keep an open mind and study all of the research, not just those that support our personal philosophy.