Body mass index, or BMI, is one way to tell if you're at a healthy weight for your height. While most people are concerned about a BMI that's too high and how it might affect health, if your BMI is too low, you may also be at risk for health issues.

While everyone is born with a genetically determined body type -- for example, a pear, apple or banana shape -- lifestyle modifications like diet and exercise can slightly change the shape of your physique.

Eating more ice cream, milkshakes and cookies sure sounds like a good way to put on a few pounds, but it's not the healthiest way to go. These foods may be high in carbs, but they're not the healthy kind.

Weight gain can pose as much of a challenge as weight loss, especially if you're naturally very thin or recovering from an illness. And while weight loss and gain plans yield different results, they share some major similarities.

Gaining weight is an important part of your pregnancy. According to W. Allan Walker and Courtney Humphries, authors of "The Harvard Medical School Guide to Healthy Eating During Pregnancy," gaining the right amount of weight will help you have a healthy pregnancy and will help your baby grow and develop right on track.

If you're on the thin side with a weight that's below normal for your height, your doctor may advise you to gain weight. Being underweight can endanger your health and may indicate that you're not getting all the nutrients you need to look and feel your best.

During your pregnancy, the amount of weight and when you gain it can vary by person. While pregnant, the average woman will gain between 25 to 35 pounds. Each trimester brings a different amount of weight gain.