How is caloric surplus an "explanation" for anything? Yes, a caloric surplus will lead to weight gain, but why do people choose to have a caloric surplus when clearly it's detrimental to health? If given the option, wouldn't you simply choose "no surplus, please"? Perhaps by searching a bit deeper we can begin to understand how the body's mechanisms attempt to regulate calorie consumption, and how we can strengthen those systems rather than subvert them.
That explains about as much as saying, "God did it."
Caloric surplus equals kilocalories in minus kilocalories out.
But kilocalories in is a function of what you eat, and of appetite, which is itself a function of metabolic processes, which are functions of a lot of variables we don't fully understand, just one of which is what you already ate. And kilocalories out is a function of your voluntary physical activity and your automatic metabolic processes, again based on variables we don't yet fully understand.
So "energy in - energy out" is a gross oversimplification. The implication there is that you can eat less and exercise more to lose weight from stored body fat. And that usually works for most people, but not necessarily for the obvious reasons. But you also have to explain all the counterexamples.
And for that, you have to figure out how the human body responds to specific food chemicals. One food with caloric value might cause the eater to lose weight because it is used for its chemical value (such as for methylation) instead. The same food might cause weight gain later, because the body no longer needs that chemical as much.
Ignoring your ignorance does not make you smarter.
That is like saying "the companies go out of business because they spend more than they earn. If you don't want to go out of business: spend less and make more."
It is correct, but not that useful to anyone who has spent more than a week trying to lose weight.
That's just shuffling the question around rather than answering it. Why are more people running caloric surpluses than before? It is not happening deliberately.
Food is much more readily available and convenient. Look at all the food you can buy. Then look at how much of it can be stored at room temperature, needs no preparation, and has a long shelf time. Then add in all that you can buy that stores in your refrigerator, does not need to be prepared, and has a long shelf life. Lets take it further, look at all the food you can buy, that you store in your freezer, that you prepare by sticking it in a microwave for five minutes.
The abundance of food combined with an excess in idle time, namely the result of a forty hour work week or no work week, leads to over consumption. I always love the farm comparison. Growing up it was eat before light, a big lunch, whatever you grabbed off the tree or stole from the garden, and a big dinner. As a kid if we weren't doing chores we were running off with friends to a game, fishing, or forever building that fort. These days its inside till mom/dad gets home, food everywhere, and an XBOX/PS4/Etc.
Then go look at the people you work with. Its pretty easy to tell why some are overweight. Lunch out every day at the fat festival around the corner, that place that serves 1200 calorie or more lunches for seven bucks. Usually a good chaser for that double donut and coffee with cream breakfast (or bagel with cream cheese). Then those little snacks in the desk.
Its simply calorie overload with nothing but idle time. Hell these same people will make fun of the fitness/diet "freaks".
TL;DR
Idle Time, Endless ready food, results in calorie overload
I'm absolutely not shuffling around the question rather than answering it.
In a practical sense, the question doesn't matter at all to people trying to live healthier lives.
The reason we have fatter people is we have more calorically dense foods readily available (meaning greater calories in) while people live more sedentary lifestyles (means less calories out).
This function to lose weight is so incredibly simple (paging jacques chester and his steam machine blog post).
A proper solution involves solving the 'Willpower Issue'. We want to address the problem in a way that can be nearly invisible to those who want to spend their willpower and intellect elsewhere. As someone in the nutrition industry, I spend a lot of my time considering what I eat, but we also have to solve the problem so that everyone can eat healthy without it having to also be a full time hobby.
Yea, it seems that people have this historical fantasy that people used to just exercise all day, and voila... were thinner. I've lived in Boston, NYC, and SF... all of which have had transit systems for a century, and people presumably lived extremely similar lives as far as passive exercise is concerned (though air conditioning is an obvious change). Still, many people in these cities are incredibly obese. The biggest difference is the automobile (for which i'm assuming these cities would be good control groups), after that, the clearest difference is food. More of it, yes, but why are people eating so much more... cost doesn't fit. It's not as though my stomach says, well these are cheap calories, better get my money's worth. No, it just doesn't make much sense if the food itself isn't causing the increased consumption.
It's probably a little more complicated: caloric surplus marketed by corporations in ultra dense, cheap and convenient hits coupled with insufficient exercise and other health/Maslow's hierarchy deficiencies. One example how bad the situation is: orange juice (the orange flavor packs kind) has more calories than an equivalent HFCS soda bottle, but I'm unsure of the glyclemic relativity... it's still sugar in a bright bottle masquerading as a healthy alternative.
