Orlando, Fla. ? Grandma, put down that Big Mac.

Seniors are supersizing themselves into serious health problems, as the number of obese older Americans has doubled in the past 20 years, according to a federal report released Thursday.

Although the alarms have been ringing for years about sedentary, overweight children, the obesity epidemic among older adults has been largely overlooked, said Richard Suzman, associate director for the National Institute on Aging.

“Everybody is surprised by it,” Suzman said.

Obesity among people age 65 to 74 increased from 18 percent in 1980 to 36 percent in 2002.

The percent of overweight people ages 65 to 74 has gone from 57 percent to 73 percent.

The comprehensive report from a dozen federal agencies released Thursday shows that, overall, older people are living longer, healthier and wealthier lives than previous generations.

But that could change if Americans don’t start eating less and exercising more, officials warn.

“Some researchers have projected that the increase in obesity, especially in the younger age groups, could bring that positive trend to an end,” Suzman said.

The consequences of obesity among the elderly include increased risk of diabetes; heart and lung disease; breast and colon cancer; arthritis and disability. In the same decades that obesity doubled, deaths among the elderly from diabetes rose 43 percent, the report said.

Experts estimate that weight-related illnesses for older adults cost the nation an estimated $30 billion to $40 billion a year in medical bills and contribute to escalating costs.