Adults who are metabolically unhealthy and obese appear to have older brains, say researchers from Harvard Medical School.

The investigators viewed brain structure and tested cognitive abilities in more than 2,100 adults ages 37 to 55. Metabolically unhealthy individuals were found to have lower total cerebral brain volume, meaning that they quite literally have smaller brains, than their metabolically healthier peers, reported lead researcher Rebecca Angoff, M.D.

Lower brain volume can lead to the loss of neurons and supporting cells, according to Angoff. “Aging, decreased blood flow and diseases like Alzheimer’s can lead to a smaller brain,” she explained.

And when these individuals were also obese, they showed more of the subtle changes to the brain’s white matter that is typical of Alzheimer’s disease. They also had lower scores on cognitive tests than the healthier participants.

“This is further ammunition for healthcare workers to convince patients to change their lifestyles and to work on early prevention with their patients,” Angoff concluded.

Participants were considered metabolically unhealthy if they were diagnosed with two or more of the following conditions: high blood pressure; high blood sugar; high blood triglyceride levels; or low levels of HDL cholesterol.

Nearly four in ten Americans are considered obese, and a quarter of adults are estimated to have metabolic syndrome, according to the American Heart Association. Studies have found that a diet high in fruits and vegetables, whole grains, fish and unsaturated fats helps promote good brain health. Likewise, regular, moderately intense physical activity has consistently been shown to improve brain function.

The study was presented at the American Heart Association’s Scientific Sessions in Philadelphia.