being skinny does not mean you are healthy

My body weight always surprises other girls, comparing to my "skinny" look. why?I do not have much fat (but more fat than I was young), I try to exercise, get more muscle than fat, it is not easy as we age. at least, I keet my SBP under 100 and pulse Less than 60.My sister-in-law is very skinny too, but her BP is around 130/98, it is very hard for her to understand that she has some artery and heart problems, because she believes that she is healthy and skinny.Healthy diet, exercise and happy lifestyle and no stress will keep you healthy and fit.I used to believe that "I live to eat" because I enjoy eating; now I believe "I eat to live" because I want to eat and live healthy.