Veganism causes eating disorders
No causal link is established. Restrictive eating disorders and ethically motivated veganism have different drivers, though an existing disorder can sometimes use veganism as acceptable cover.
Veganism trains people to scrutinise every meal, read every label and rule out whole categories of food, and that habit of rigid restriction is exactly the pattern that defines anorexia and orthorexia. Clinicians report that vegan and vegetarian diets turn up far more often among eating disorder patients than in the general population, which suggests the diet is doing real harm. Because cutting out foods in the name of ethics earns praise rather than concern, the restriction can grow unchecked until it becomes an illness.
Reviews of the evidence have not found that vegan diets cause eating disorders. The association that does appear in clinical samples is better explained in the other direction: a person with an existing restrictive disorder may adopt a socially respectable framework that licenses excluding foods, and veganism can serve that purpose.
The distinction matters clinically. Restrictive disorders are driven by fear, control and body image; ethical veganism is driven by a moral commitment about other beings, and is associated in research with motivations quite unlike disordered eating. The practical implication is that clinicians should ask what is motivating the restriction, not that ethical veganism should be treated as a warning sign.
Inferring that one thing caused another from the fact that they occurred together or one after the other. Correlation and sequence are not causation.
How it applies here: Observes that the two sometimes occur together and infers that one produces the other. The better-supported reading runs the other way (an existing disorder adopts an acceptable framing.
Drawing a general conclusion from a sample too small or too unrepresentative to support it.
How it applies here: Draws a conclusion about vegans in general from the subset who appear in eating disorder clinics, a sample selected precisely for disordered eating.