If you're overweight, your primary care physician will help assess the role your weight plays in your knee pain and recommend a plan of treatment accordingly. Most likely, a plan for weight loss will be part of your treatment. Many knee problems can be avoided by maintaining a healthy weight.
Carrying extra weight is directly related to knee pain. A 2008 review article in the journal Obesity found that obesity (defined as having a body mass index of 30 or above) leads to pain, limits activity, and increases the risk of needing a total knee replacement. In 2003, Obesity Research published a study of 5,700 Americans over age 60. It showed that the more obese a person was, the more likely he or she was to experience knee pain. About 56% of severely obese people had significant knee pain, compared with 15% of people who were not overweight.
Such findings are not surprising when you consider that with each step on level ground, you put one to one-and-a-half times your body weight on each knee. So a 200-pound person can put 300 pounds of pressure on each knee with each step. The burden is even higher when you go up and down stairs (two or three times as much weight) or squat (four or five times). So if you're 50 pounds overweight, the simple act of going downstairs and squatting to move clothes from the washer to the dryer puts hundreds of extra pounds of force on your knees.