Forget everything you thought you knew about calories and weight gain. Turns out fat or thin is determined by the human microbiome, the community of microbes (bacteria) living in your digestive tract.
So that explains why simple low calorie diets don’t work or work well, and why weight gain can happen with medications even though diet has not changed.
Perhaps America is “getting fat” due to a spread of certain types of bacteria present in the food supply, and then that can correlate to amounts of food in some ways. It would make sense.
Then health and weight would hinge on what you eat, not necessarily how much. It’s why families will be fat families or thin families, because they are sharing habits that are favorable to the particular combination of bacteria that make up the human microbiome.
More study will have to go into the theory, but certainly makes more sense than the calorie theory. A calorie, after all, is only how hot something burns when you set it on fire. Of course fats or oils will burn hotter, and anyone who has made syrup knows sugar burns hot. But your body is not lighting food on fire, and it is the types of microbes in certain foods that are the greater factor for determining if a human being is fat or thin.
For now, it looks like there is a correlation to amounts of bacteria, and thinner people have more microbes and a greater diversity of bacterium in their digestive tract than fatter people. And also, it seems that health in general is improved when there are greater amounts and greater diversity to all those little critters making a home in the human gut.