an eating disorder starts with an energy deficit, and this is true for literally every ED. the causes of energy deficits are innumerable but some common ones are:
poverty
food insecurity
housing insecurity affecting ability to prepare food
working jobs with no break to eat
unsafe living environments
stress induced loss of appetite
lack of safety in kitchen and eating spaces
food and body based abuse (disparaging eating choices & weight)
diet culture babey!
every restrictive diet in existence, incl wellness diet lifestyle change