- Throughout most of human history, people were pretty damn active. It's only recently, within the past 5 decades, that inactivity has become the norm.
- Diabetes is chronic resistance to insulin; it is not "taking insulin". Diabetics gain weight not because of insulin, but because they are
resistant to insulin, so the body is unable to properly break down food; more of it ends up being converted to fat so the body can try to break it down later.
- Fat is not an energy battery. Carbohydrates are for energy. Fat is for providing nourishment when food is not readily available, and for warmth.
- Damage from starvation is not to fat, it's to muscles. Muscles are high-maintenance tissues. If there aren't enough nutrients to maintain them, they break down. It only takes a day or two of fasting for this to occur; the longer the fasting period, the greater the damage.
- Weight management is about calories consumed versus calories expended. If you want to call that thermodynamics, so be it, but it demonstrates that you don't understand what thermodynamics is, or that you don't understand how the human body works.
- My science is medical science. It's backed by prevailing medical opinion. Hell, I made sure to check WebMD and various other medical sites to make sure i wasn't pulling it out of my ass.
It's very simple: eat more than your body can convert into energy or expel through various bodily functions, and that remaining mass remains in your body, as fat. Too much of that fat, and you have "obesity".
Puberty is red herring. However, medical science has shown that puberty is triggered by the quantity of food one eats -- suggesting a mass trigger for puberty, which explains why fat little boys and girls hit puberty early, but gymnasts look like little girls into their 20s.