FWIW it is certainly well established as a contributing factor. The cincher as a major cause would be if there was evidence that as regional antibiotic consumption increased (through both medical use and consumption of foods contaminated with antibiotics used industrially in food production) obesity rate increases followed.
Both of these are based on the same implicit assumption that decisions of how much to eat are for most people (thin and fat alike) rational thought out processes. The brain is the main driver of how much we eat and how much we burn but for most of humanity and certainly for most of humanity’s history, not at that conscious calculated level. “Counting calories” is indeed based on poor data at many levels, but it is also a very recent thing in human history. People are not operating with worse data in recent decades, or more poorly educated about nutrition, than several decades in the past, and poor nutrition education and poor calorie data has not spread across the globe as a contagion.
The brain is in charge by making declarations about when we are hungry and when we have had enough and when something tastes good enough that we will go past those signals some. The brain is in charge by controlling calories out in ways far above and beyond a decision to exercise daily, but in how much we move when and burn when not exercising throughout the day. These things control our conscious thoughts perhaps and they are not the direct result of our conscious thoughts.
And our brains do these things in response to our environments, inclusive of the nature of the foods we are surrounded with, the timing of when we eat it, what messages our guts send to no small degree impacted by our gut microbiota, and the impact of activity even more on our brains than on the activity burned during exercise or as a direct effect of recovery from it.
Of course no duh that more calories in than out results in energy stored. But citing that as an explanation is being completely ignorant of how the human machine is very dynamic in both parts of that equation. It has always been so. So what has resulted in the global spread of in net taking in more calories than we burn over long terms? Have humans across the globe fairly suddenly caught a germ that saps will-power and self-discipline, spreading it from America to elsewhere over decades?
QtM is completely right when we are thinking of our own individual circumstances. We cannot control the huge environment around us, whatever those factors are. Lots of reasons to advocate for good antibiotic stewardship, to be sure we ask if we really need to take the antibiotic or if watchful waiting is a better choice, and to demand less antibiotic use in the industrial food chain, lots of reasons to advocate that kids not be taken advantage of by the Food Industrial Complex, but we can only control what we do, our personal behaviors, putting better choices on our plates in smaller portions and exercising more.
But at the larger level of analysis, it is like explaining a specific global flu epidemic taking off by saying you catch influenza by not having washed your hands and not having gotten vaccinated.
Now everyone go and overeat your turkeys!!
