However if you are not then nutrition plays a key role and not all calories are equal on a macro level, and more importantly more and more it seems that there are better and worse combinations of calories.
People that cut out carbs experience a lowered appetite, more stable blood sugar levels and are less likely to accumulate fat as their main energy cycle will be either ketogenesis or glucogensis depending on the fat to protein ratio they consume on a low carb diet, with Keto seem to be the most effective at maintaining lean body mass.
Now are there long term negative effects of such diets? maybe, are there better diets? also maybe.. I was also very skeptical about this until I tried both a ketogenic and carnivore style diets and despite consuming 2800 kcal a day (I’m only 181cm) I’ve seen very impressive results. And don’t get me wrong I was and am still active mainly running and with the exclusion of a 2 week set back when I tried Keto in both cases my running performance was better at the end than on a balanced diet with pre-run carb loading.
It's just extremely hard to properly track what you're eating if you're unwilling to pay attention to it, which I don't blame people for.
There's so many calorie dense foods because we wind up adding sugar and oil to so many things when we process them and you don't even realize how many calories you're bringing in.
It ain't easy out there!
I’m keen not to blame people for their weight, I’m keen to make sure we are researching the right problem. I think the “how to control weight” is solved, the harder problem, as I mentioned in a previous comment above, is how do me help people control the appetite and impulses to stand a fighting chance.
My concern is that while the obesity problem is getting worse we are looking for more and more complex reasons when in reality most people consume more calories than they require.