It's just our human mind, being human mind, makes us thinks of foul smell around fat people can alter our sense of smell, making everything around us smell less pleasant than usual. Viewing images of fat people actually cause the study participants to rate an odour of the sample to have smell worse, even though those samples are fragrance fee. It is believed that the effect might be caused by our subconscious negative bias towards who are fat, many people has this bias apparently. Moreover, people with higher weights rate the smell to be worse too. So your brain is your own body’s harshest critics. Fragrance are perceived by the human brain to have smell worse just with a pairing of an image of a fat person that when they are paired with a thin person, a subconscious disgust signal. There is this weird assumption that fat people just smell bad, even though in all actual facts, they don’t. We just aren’t aware of it due to our bias to make weight problems to be much worse. So it’s our brain is just honest with the fact that it doesn’t like having fat people around.