Researchers tracked the health of more than 6,000 British people, aged 35 and 55, over a decade. They took tests on memory and other cognitive skills three times over that 10-year period.
What they found was that people who were both obese and who had unhealthy metabolic changes showed a much faster decline on their cognitive test scores compared to others in the study.
In their findings they stressed that they looked only at cognitive function – neurologically speaking that means any mental process like perception, memory, imagination, thinking, awareness and judgment.
The fastest cognitive decline was observed in those with both obesity and metabolic changes such as higher blood sugar and raised cholesterol.
Shirley Cramer of the Alzheimer's Research UK said: "We do not yet know why obesity and metabolic abnormality are linked to poorer brain performance, but with obesity levels on the rise, it will be important to delve a little deeper into this association.”