A recent study - published in the Journal of Alzheimer's Disease - reveals that people aged 70 and older who consume a high carb diet have nearly four times the risk of developing mild cognitive impairment (MCI) relative to their peers who consumed more protein and fat. The risk of developing MCI was also seen to increase with high sugar levels in the diet.

MCI is a brain disorder normally associated with aging. People with MCI are able to function independently, but they typically find it difficult to remember the names of people they’ve recently met or follow the flow of a conversation. While MCI is not dementia, many people with MCI are eventually diagnosed with Alzheimer's disease (AD).

The Mayo study looked for a possible link between the percent of daily energy (calories) obtained from macronutrients in the diet - protein, carbohydrate, and total fat - and the likelihood of developing MCI or dementia.

In total, 1,230 study participants between the ages of 70-89 filled out a 128-item food frequency questionnaire at the start of the study. Total daily caloric and macronutrient intakes were calculated, including percent of total daily energy obtained from protein, carbohydrate, and total fat.

At the start of the study and every 15 months afterwards, participants were also evaluated using the Clinical Dementia Rating scale and neuropsychological testing for a diagnosis of MCI, normal cognition, or dementia.

Of the starting participants, 940 showed no signs of cognitive impairment and were asked to return for follow-up evaluations. In the 4th year of the study, 200 of these participants started to show MCI and developed problems with memory, language, thinking and judgment that were more severe than expected at their age.

Interestingly, the study found that the highest carb consumers had a 1.9 times higher MCI risk than those who ate the least carbs. Similarly, those who consumed the most sugar had a 1.5 times higher MCI risk compared to the lowest consumers. On the other hand, participants who consumed the most fat had a 42% lower risk of developing cognitive impairment compared to those who ate the least fat. The highest protein consumers also had a 21% lower chance of developing MCI compared to the lowest consumers.

Overall, the study revealed that the highest consumers of carbs had a 3.6-fold greater chance of developing MCI - clearly indicating the critical role of high carbs and sugar in the development of aging-related MCI.

And now, exciting new research shows that high carbohydrate intake may be adversely impacting glucose and insulin metabolism - and that high levels of sugar may itself be preventing the brain from using sugar properly, similar to the situation seen in type 2 diabetes.

Not only that, there’s mounting evidence that AD may at least partly be caused by neuronal insulin resistance. In other words, AD may be a form of brain diabetes. However, it’s not yet clear whether type 2 diabetes contributes to MCI and the brain damage seen in patients with AD.

Reduced glucose utilization and deficient energy metabolism are known to occur early in AD, suggesting that impaired insulin signaling may play a role in this disease. There are also extensive abnormalities in insulin and insulin-like growth factor type I and II signaling mechanisms in AD brains.

All this suggests that AD may resemble type 2 diabetes mellitus. In fact the term ‘Type 3 Diabetes’ has been proposed for AD to reflect this newly identified mechanism of how neurons in the brain can be damaged by impaired insulin signaling and impaired glucose utilization.


High carb and high sugar diet speed up mild cognitive impairment (MCI) in the elderly.