The Negative Health Effects of Being Underweight In today's health conscious world, most people are more worried about being overweight. Excessive weight gain and morbid obesity can lead to heart disease, stroke and a host of other medical issues. On the other side of the issue, extremely low body weight can also have negative effects on a person's health, especially women. Reasons for Low Body Weight There are several reasons why a person's weight fluctuates. When it begins to fluctuate more than a few pounds at a time, a person should begin to wonder why. While changes in diet and activity levels will be responsible for mild changes, dramatic changes will need to be discussed with your doctor. There are several reasons a person may experience a severe drop in weight or is unable to gain weight. Recent illness Changes in metabolism Excessive drug use Extreme levels of stress Depression and other forms of mental illness Poor diet If a person suffers extreme weight loss due