It is a separate set of DNA within all our cells which comes through the mother and is used to track how old is our species and our diversity.
What it shows is humans spent most our time nearly extinct, and become dominant in relatively recent times.
Also our species has developed an ability to consume large amounts of food during times of excess food, to then burn in times of insufficient food. Humans not unique, Polar Bears, Whales, etc. can do similar. That tells us that in forgotten history, the fat kid lived and the skinny one didn’t.
The existence of excess body mass does, agreed, cause the human to need more energy to maintain the food. i.e. fat people need more food to maintain, so yes, a person who maintains excess weight is taking food from someone else, needlessly.
Food challenges is not that. The challenger has to spend time not eating days either side before and after. If they did not they’d end up so much larger you could spot it from their dimensions.
As to your video - look up Mr Creosote. Wafer thin.