I'm not saying they don't also do unnatural things to their bodies that set unrealistic standards and don't set a good example, but being "thin" is not one of them.
I'm not saying they don't also do unnatural things to their bodies that set unrealistic standards and don't set a good example, but being "thin" is not one of them.
* are used to not snacking between meals
* eat when they are hungry, and stop when they are not
* do not drink (excessively)
* are more-than-average active
Calories add up extremely quickly and it's very easy not to notice if you don't pay attention. Say you have one Mars bar per day, as a snack - that makes a difference of 10 kg of body weight per year as compared to someone who skips such a snack (a back-of-the-envelope calculation).
I did read a study on non exercise thermogenesis and how some people managed to burn quite a bit of calories just fidgeting throughout the day.
So while we all run around the same human body temperature and thermodynamics is all the same, different people arrive at different results because of different behaviors. To what extent they are genetic is up to debate but much is genetic like “a tendency to fidget” or “a tendency to like sweets”.
There are certain breeds of dogs and cats that will eat until it makes them sick and easily get fat. Other breeds don't. Even with food readily available they just don't get fat. Humans are no different.