Toni Watson has gained 127 pounds since her high school days
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LOS ANGELES (CNN) -- Lugging a few extra pounds to your 20th high school reunion could damage more than just your vanity - - some doctors say it could make you twice as susceptible to serious diseases.

"Just 25 pounds weight gain since high school could result in doubling your risk for breast cancer, for colon cancer, for hypertension, for diabetes ... and many common ailments," said Dr. Keith Doram.

About 97 million adult Americans -- including about 40 million baby boomers -- are overweight or obese and face increased risk of chronic illness, according to National Heart, Lung and Blood Institute guidelines.

The American College of Physicians-American Society of Internal Medicine is urging bulging baby boomers to get medical check-ups to avert early complications of serious disease associated with being overweight.

While a gain of 25 pounds spread over 20 years may not seem like much, it could have a big impact on your body mass index (BMI) -- a computation of height and weight.

BMI is calculated by multiplying weight in pounds by 704.5, then dividing by height in inches squared. A desirable BMI is 21. A BMI of 25 to 29.9 is considered overweight and obesity is 30 or higher.

Toni Watson, who said she's gained 127 pounds since she graduated from high school two decades ago, is in the danger zone with a body mass index of 30. She recently developed diabetes.

"I just wish I had known 20 years ago what I know now," she says.

Correspondent Jim Hill contributed to this report.