High Carb Diets Are Associated with Early Cognitive Decline and Alzheimer’s Dementia

by Dr Sam Girgis on October 19, 2012

Mild cognitive impairment is the decline of mental function that goes beyond what would be expected based upon the age and education of an individual. This type of cognitive decline does not interfere with the regular activities of daily living. Mild cognitive impairment is usually diagnosed when there is evidence of memory impairment, preservation of general cognitive function, and absence of a dementia diagnosis. Mild cognitive impairment can be a precursor to more severe mental functional impairments, such as Alzheimer’s dementia. There are several risk factors for the development of mild cognitive impairment and dementia. These include high blood pressure, type 2 diabetes, smoking, and obesity. Recent research has found that high carbohydrate diets may also be a risk factor for early cognitive decline.

Researchers, led by Dr. Rosebud O. Roberts from the Mayo Clinic, have found that elderly individuals who consume a diet high in carbohydrates have increased risk of developing mild cognitive impairment or dementia. The results of their study were published online in the Journal of Alzheimer’s Disease. The researchers conducted a population-based prospective cohort study among 937 individuals with a median age of 79.5 years. The subjects were free of dementia at baseline and were followed for a median of 3.7 years. The study participants were assessed with neuropsychological testing using the Clinical Dementia Rating Scale at baseline and every 15 months. The study participants completed a 128-item food frequency questionnaire and macronutrient intake was calculated. The researchers found that study participants with diets high in carbohydrates and low in fat and protein were 3.6 times likelier to develop mild cognitive impairment.

The authors wrote, “In our population-based cohort of elderly persons, high % carbohydrate intake was associated with an increased risk of [mild cognitive impairment]. In contrast, high % fat and high % protein intake were associated with a reduced risk of [mild cognitive impairment] or dementia. These findings suggest that dietary patterns consisting of a high intake of energy derived from carbohydrates and a relatively low intake from fat and protein may have adverse implications for development of [mild cognitive impairment}”.

The authors explained, “Glucose is a major source of energy for brain metabolism, and glucose administration typically enhances cognitive performance. However, in elderly persons, a dietary pattern high in carbohydrate intake and in simple sugars may disrupt glucose and insulin metabolism. High insulin levels may be detrimental to cognitive function… The increased risk of [mild cognitive impairment] with lower intake of fats and proteins may involve non-energy related pathways. Fat and protein intake may be required for the integrity of neuronal membranes and fats for the integrity of the myelin sheaths in the brain”.

This study identifies high carbohydrate diets that are low in fat and protein to be associated with increased risk of developing mild cognitive impairment and possibly dementia. The finding is an association and it is important to note that a causal relationship has not been established. High carbohydrate diets may contribute to insulin resistance and interfere with brain glucose metabolism. In addition, as the authors suggest, low fat and protein intake may interfere with the normal function of neurons. The exact mechanism of the finding need to be further investigated. One limitation of the study was that study participants were asked to recall from memory the type of diet that they had consumed. These findings will need to be reproduced, but suggest that a low carb diet may be beneficial for delaying the onset of mental decline in older age.



Rosebud O. Roberts et al. “Relative Intake of Macronutrients Impacts Risk of Mild Cognitive Impairment or DementiaJournal of Alzheimer’s Disease 32 (2012) 329–339
DOI 10.3233/JAD-2012-120862

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