This is the case with a friend of mine. This boy has been very thin since he was a child. He looks skinny, not fleshy. For him, his stomach is weak and he often has diarrhea. Every time I have dinner with him, he eats more than me, but he just puts on weight. Mainly because his digestion and absorption are very bad every time, because his stomach is not good, that is, his nutrition absorption is insufficient, his constitution is weak, and he is prone to illness. I think this constitution is not good. Some of them are caused by diseases.
In addition to the above reasons, diseases can easily lead us to get fat. A friend of mine has diabetes, which belongs to the constitution that eating alone will not make him fat, because a lot of energy disappears after eating, and he will not get fat unless he is absorbed by the human body. Such a constitution itself is unhealthy, how can it be good? Everyone should pursue a healthy body.
I don't think we should pursue the physique of not eating fat. Although eating is very comfortable for us, it is easy to get sick when we are weak. This is not a healthy constitution. Everyone can keep a good figure, which can be done by controlling diet and exercise, but gastrointestinal weakness is really not a good constitution.
In a word, I don't think you will get fat no matter how you eat it, because on the one hand, many people have weak stomachs, so their physique is poor, and they won't get fat if they eat it alone, and some people are sick. For us ordinary people, we should still keep a healthy body.