Maintaining the right body weight may just be the ultimate key to your health.

Many Americans are considered overweight or obese. Obesity is tied to a body mass index of 30 and above, calculated by a combination of a person’s weight and height. An overweight person has a BMI of 25 to 29.9; extreme obesity is linked to a BMI of 40 and above.

In children, being overweight or obese is classified according to a percentile.

More than 2 in 3 adults in the United States are considered to be overweight or obese, according to findings from the National Health and Nutrition Examination Survey in 2009-2010. More than one in 3 are considered obese; more than one in 20 have extreme obesity.

These aren’t just numbers, says Dr. G. Edward Mallory, a board-certified physician who has been practicing emergency medicine for more than 20 years and serves as an expert witness in medical malpractice cases. People who maintain a healthy weight are sick less, have more energy and have a better and longer life.

Risks associated with being overweight include diabetes, high blood pressure, osteoarthritis, certain cancers and heart disease.

Dr. Mallory suggests that everyone should keep track of their cholesterol, blood pressure and triglycerides, a type of fat in your blood.

If your cholesterol is too high, you may be at risk for heart attack or stroke. Medicine may help.

If you need to try medication or go on a diet, discuss options with your doctor. Schools and hospitals also have dietitians. You can customize your diet depending on your condition – your needs may range from lower calories to higher protein.

Avoid what Dr. Mallory calls “joke diets” — fad diets that are more about their creators making money than about achieving good health.

That said, some established diet strategies, such as Weight Watchers, appear to be balanced and effective. Get advice from your doctor to determine what’s right for you.