Probably the biggest lie that diet culture has ever sold us is that naturally thin people are an exception and a rare occurrence.
In reality, people who stay a specific body type no matter how they eat or how much they exercise are the norm. Genetics have been scientifically proven to be such a huge factor in weight that they explain at least 70% of variance, which is the same range of a role that genetics plays in height. And that other 30% isn't even just food or exercise. It also includes factors such as socioeconomic status and disability, which are not choices either.
There are so many thin people who THINK they're thin because they're "good" and "have put in the work," but in reality if they stopped going to the gym three times a week and ended their vegan-organic-kale-keto diet (or more often than not they'll think drinking smoothies every other day is all that's needed to achieve thinness), they will still continue to be thin. Society pushes us to believe they're thin because of whatever diet culture things they do, but we have had an enormous amount of scientific evidence for decades upon decades that proves things like dieting legitimately Do. Not. Work. The vast majority of thin people are thin because that is what their genetics, their body, has determined is the shape that works for them. It is not because they eat a salad on Fridays and Sundays or because they drink protein shakes.
Have you ever stopped to think about how you have never heard of naturally fat people despite naturally thin people being an accepted fact? But if you talk to any fat person and actually ask about their own experiences, you will hear things like how they have been on diets their whole life, how they extremely restrict, how they try every new diet culture product, but absolutely none of that has caused them to become a permanent thin person. No matter what they do, their body always falls back into the body type they've always had.
For the longest time I believed I must eat more than thin people and exercise less than them, but I really don't. And there are so many fat people who eat even less than most thin people because almost every single fat person out there is trying desperately to become smaller like society demands of us.
And this isn't to say that eating little and exercising a lot are morally good. This is to say that all the people who believe that is all you have to do to become a thin person are extremely ignorant on unbiased weight science and the reality of what most fat people are already doing.
Naturally thin people are not rare. They are not an exception to diet culture. They are the proof that diet culture is one of the biggest scams in human history. The majority of thin people, mid-size people, and fat people have that body type because they are naturally that way. And even if a fat person is fat because of the most "immoral choices" you can think of, that does not automatically tell you their health or give you a pass to treat them like the dirt underneath your feet. They still deserve basic human dignity and respect because fatness does not mean they are not a fellow fucking human being.
Stop assuming that someone's fatness is a choice or even your business. Stop believing the lies of diet culture.