Most of us can only dream of being able to eat what we want and not earning an ounce. Being underweight is much worse for your health than being overweight.
Obesity is associated with a 50% higher risk of premature death. Underweight is associated with a 140% higher risk for men and a 100% higher risk for women.
The lack of weight gain can be a symptom of a serious underlying condition, which includes eating disorders, thyroid problems, diabetes, cancer, and chronic infections.
Talk to your doctor first, and then check out these tips for healthy weight gain. Interestingly, many of these weight gain tips are also those that help other people lose weight.