But the reverse is not by all means true. If you have a BMI of under 17.5 it doesn't follow that you have anorexia. It's basic logic.
I wonder, but can't find, how many people with a lower BMI actually have anorexia.
All I can say is that I have a similar height to Cheryl and similar body, so it's fair to assume that we have very similar weights. My BMI, even at my lowest weight, has always been above 17.5, and thus above what would be considered at risk for anorexia.
People can't just throw about their estimates about her BMI without actually knowing her weight or having a realistic point of reference.