It's not that being underweight causes disease, but that these chronic diseases can cause weight loss, ... It's called reverse causation.

It's similar to having a family history for a disease. You can't alter your family history or your baldness, but there are many ways to modify your risk factors,

The effect of cigarettes on the risk of disease is so powerful and it's so difficult to control for factors like the intensity and duration of smoking that the only way to eliminate the bias is to look at people who have never smoked,

There is no magic pill for weight loss.

They run high fevers, their mouths are sore, they don't eat well, they lose weight; very debilitating disease.

Weight doesn't matter as long as you're happy with yourself.