If he slims down quickly, find out why.

05-28-09 RODALE NEWS, EMMAUS, PA—Fans of The Biggest Loser were probably impressed to see Jerry, the 63-year-old grandfather, beat out younger, more agile dieters by losing 177 pounds (nearly 48 percent of his original body weight) by the show’s season finale last May. But when that that kind of rapid weight loss happens in older folks without intervention from TV fitness coaches or some other deliberate cause, it can be an early sign of Alzheimer’s disease or other forms of dementia, according to a new study published in the journal Neurology.

THE DETAILS: For approximately eight years, the study authors followed 1,478 Japanese Americans living in retirement communities or nursing homes in Washington State. The average age of the participants at the start of the study was 72, and their average body mass index (BMI) was 24.3. (In Japanese people, 23 is considered the upper limit of normal, overweight is defined as 23 to 25, and obese is a BMI over 25. Americans are considered overweight or obese at slightly higher numbers.) The higher the BMI at the start of the study, the authors found, the lower the person’s chances of developing dementia or Alzheimer’s disease by the study’s end. People who experienced rapid, unintentional weight loss were nearly three times more likely to develop dementia than people who shed pounds at a slower, steadier rate.

WHAT IT MEANS: “Any weight loss in older adulthood that’s not associated with dieting on purpose should be cause for alarm,” says study author Tiffany Hughes, PhD, MPH, a postdoctoral scholar at the University Pittsburgh School of Medicine, who performed her research while getting her doctorate at the University of South Florida. Rapid weight loss, she adds, doesn’t cause dementia, but it is an early marker and could be a signal for other health problems.