Researchers at University College London said the study was based on data from 6,500 federal British civil servants, whose health was monitored from the ages of 50 to 60, The Daily Telegraph reported.
The study participants were weighed, measured, blood pressure and cholesterol tested and they were also asked about any medication they were taking.
The study participants were asked to perform mental tests three times during the decade, which were used to assess memory and other cognitive skills.
Of the 6,401 civil servants, 9 percent were obese and of those, 350 were "metabolically abnormal," meaning they had two additional risk factors such as high blood pressure, high cholesterol, were taking medication for either condition, or had diabetes.
The study, published in the journal Neurology, found the obese tended to lose their mental powers faster than their thinner colleagues. In addition, those who were obese and also had additional conditions such as high levels of blood pressure or cholesterol experienced a 22.5 percent faster decline on their cognitive test scores over the decade than those who were healthy, the study said.