Some[1] will never drop the "simple physics" line because they don't care about learning about the biology of body weight, but rather reaffirming their aesthetic judgement that people they decide are overweight are also morally weak.
[1] Emphatically not judging anyone posting here; that's not my goal. I'm simply bluntly stating what has become painfully clear after having this discussion multiple times.
And some will endlessly argue against “simple physics” because magical thinking about metabolism avoids any hint of personal agency.
In a sense, the body isn’t “simple” because so many things can affect your total energy burn. But all of that really doesn’t matter much. If you continually decrease your caloric intake, eventually it will fall below your calorie burn and you will lose weight. Conversely if you continually increase your caloric intake, you will eventually gain weight (assuming you aren’t literally shitting out undigested food).
It’s not about aesthetic judgement. If you won the genetics lottery and have a high metabolism, you will have more calories out. If you won the genetic lottery and grow to be 7 feet as oppose to be 5 foot 5, you will burn more calories and find it easier to be slim.
I didn’t win the height genetic lottery or the higher than average metabolism genetic lottery, but I did win the mesomorph one. I naturally look muscular whether I lift or not and I pack on muscle quickly. That isn’t due to any moral strength.
Are you really saying that different people don’t naturally have different body types? I’m 5 foot 5 and 175 pounds. Based on BMI, I am “morbidly obese”. But I have a 32 inch waist, muscular looking legs and an objectively toned upper body with little body fat measured with calipers - 6 points. It’s not because I am a body builder. I’ve had this same basic shape whether or not I was lifting and I only occasionally been to the point where I lifted heavy.
I’ve seen other people my same height and weight with large stomachs and no tone and with a completely different waist to hip ratio.
That’s exactly what a somatype is. Some people also naturally gain muscle easier. Do you think that if your average person and a top tier athlete train the same amount of time they will have similarly outcomes?
[1] Emphatically not judging anyone posting here; that's not my goal. I'm simply bluntly stating what has become painfully clear after having this discussion multiple times.