Only diseases? I'm three years into life sciences and that question doesn't really make sense.
It depends at which lense you look at it through. Epidemiology and public health look at it on a huge statistical scale, there's diseases there. Biochemistry looks at diseases like diabetes and other things at their very lowest chemical level. Slightly higher you have things like microbiology or immunology looking at the causes or responses. Slightly higher again you have things like physiology, anatomy or pathology looking at it at an functional-organ level. You have pharmacology where you look at drugs to treat the disease. Nutrition where you look at problems as a lack of nutrition.
You can't really just study a disease (unless its one of those "cool fact" or horrible history books) unless you find a lens to look at it through. Most life science subjects will heavily feature diseases, it's a pretty sure bet.