Keeping a trim waistline as we age isn't all about a healthy diet. Researchers have found that the older we get, the more exercise plays a significant role in keeping fit — more so than diet.

The study, led by Russell Pate, was published in the journal of Medicine & Science in Sports & Exercise. It examined 4,999 American adults between the ages of 20 and 70. The data was taken from a survey from the National Health and Nutrition Examination Survey, which recorded participants' information regarding BMI, weight, waist circumference, and diet.

The researchers found that while older age groups maintained better dieting practices, their waist circumferences and BMIs were higher than the younger groups. The only age group whose waistlines seemed to benefit from a healthy diet alone were men age 30 to 59 and women age 50 to 59. But across all age groups, researchers noted there was an inverse effect on people's waistlines and BMIs for those who partook in some form of moderate exercise.

The researchers concluded:

“[Moderate to vigorous physical activity] was very consistently related to weight status in both genders. The relation between diet quality and weight status was less consistent. These findings provide support for public health efforts to prevent obesity by promoting increased physical activity in adult Americans.”

Pate recommends that people stand by the federal guideline that states people should aim for about 150 minutes of physical activity every week. “If most American adults met that guideline, rates of overweight and obesity would be substantially lower than they are today,” Pate said in an interview with The Huffington Post.

Not only that, but as Patricia Bloom, associate professor of geriatrics at Mt. Sinai, explains, for older folks who want to keep their mind sharp, exercise can help preserve those cognitive functions:

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