This is the correct answer. The example person is about 177cm and 110kg, i.e., a clearly fat person, trouble moving and likely some problems with breathing already. If he doesn't have a metabolical disorder, with that amount of body mass, it should be _really_ easy for him to drop weight by reducing calorie intake -- just by not constantly eating or drinking. But since he's used to eating like a pig, it's not so easy. And I'm not saying this to mock him, it's a fact of how his body has adapted to eating lots of calories.

A single Mars bar can contain the calorie count of half of a meal, which is why these people are not losing weight. After all, it's just a Mars bar!