The amount of people I’ve seen claim they eat 500 calories and don’t lose, or even gain, weight is ridiculous. There are no adult humans consuming 500 calories a day for an extended period of time and are not starving and losing weight at a massive rate. A 1 year old baby, weighing roughly 20 lbs, needs 1000 calories a day. You are not 200 lbs while eating less than that on a regular basis (without binging).

The medical claims are also ridiculous. Your body needs a certain amount of calories to stay alive. This does not vary that drastically. PCOS is a common excuse thrown around. There are conflicting studies, but it appears that PCOS does not dictate BMI the way Redditors would have you believe:

https://pubmed.ncbi.nlm.nih.gov/30496407/

https://pubmed.ncbi.nlm.nih.gov/32163573/

People who claim they don’t eat that much and are obese underreport their intake and overreport their physical activity:

https://www.nejm.org/doi/full/10.1056/nejm199212313272701

Just watch Secret Eaters or Supersize vs Superskinny. Not one person who swears they barely eat is telling the truth. Whether it is intentional is irrelevant; the point is that there is literally nothing stopping anyone from losing weight.

I have no problem with people being whatever weight makes them happy. I have a problem with people pretending that their inability to try is based on excuses that may influence someone else to not try. Anyone can lose weight. There are zero diseases or medications that make weight loss impossible.