Older people, who eat a carbohydrate rich diet are four times more likely to develop mild cognitive impairment, which is a precursor to Alzheimer's disease, a new research has claimed.

The research from the Mayo Clinic in America has found that the risk is also higher with a diet high in sugar, while on the other hand, proteins and fats appeared to offer some protection as people who consumed plenty of them were less likely to suffer cognitive decline, the Daily Mail reported.

Not everyone suffering from mild cognitive impairment (MCI) develops Alzheimer's disease, but many do, lead author Rosebud Roberts, a professor in the department of epidemiology at the Mayo Clinic, said.

The research tracked 1,230 people of ages between 70- 89 and asked them to provide data on what they ate last year.

Among that group, only 940 people who showed no traces of cognitive impairment were asked to return for follow-ups every 15 months.

By the study's fourth year, 200 of the 940 began to show mild cognitive impairment - trouble with memory, language, thinking and judgment.

"If we can stop people from developing MCI, we hope we can stop people from developing dementia. Once you hit the dementia stage, it's irreversible," Professor Roberts told USA Today.

"A high-carbohydrate intake could be bad for you because carbohydrates impact your glucose and insulin metabolism.

"Sugar fuels the brain, so moderate intake is good. However, high levels of sugar may actually prevent the brain from using the sugar - similar to what we see with type 2 diabetes," she added.