First author Rosebud O. Roberts, MD, ChB, an epidemiologist at Mayo Clinic in Rochester, Minnesota, wrote, an "optimal balance" in the proportions of daily calories derived from carbohydrates, fat, and protein may help "maintain neuronal integrity and optimal cognitive function in the elderly."
"We think it’s important that dietary intake of fats, carbohydrate, and protein is balanced because each of these macronutrients has a specific role in the body," said Dr. Roberts in a Mayo Clinic podcast.
"A high-carbohydrate intake could be bad, because they affect how glucose and insulin function in the brain. If there is dysfunction in glucose and insulin metabolism, it affects the brain," she added.
"Some people have described mild cognitive impairment as having diabetes in the brain because the sugar affects your brain in a way that is not good if you have too much of it, so with carbohydrate, we think that’s what could be happening," Dr. Roberts said.
The role of dietary macronutrients, including carbohydrates, fat, and protein, on brain function in older adults is a fairly understudied area, the investigators note. They investigated the association between percent daily energy intake from macronutrients and incident MCI in a population-based prospective cohort of 937 initially cognitively normal adults aged 70 to 89 years. During a median follow-up period of 3.7 years, 200 developed incident MCI or dementia.
According to the researchers, in a fully adjusted model, the risk for MCI or dementia was higher in participants in quartile 4 vs quartile 1 of carbohydrate intake at baseline (>58% vs <47% total energy). The hazard ratio (HR) for quartile 4 vs 1 was 1.89 (95% confidence interval [CI], 1.17 – 3.06; P for trend = .004).
Similarly, in participants with the quartile 4 vs quartile 1 for sugar intake (>27 vs <19% total), the HR for MCI was 1.51 (95% CI, 0.94 – 2.41; P for trend = .05).
The risk for MCI was reduced in participants with the highest total fat intake (>35%) compared with the lowest (<27%). The HR was 0.56 (95% CI, 0.34 – 0.91; P for trend = .03). It was also reduced in persons with the highest vs lowest total protein intake (>20% vs <16%), the HR coming in at 0.79 (95% CI, 0.52 – 1.20; P for trend = .03).
In a multivariable model that included carbohydrate, fat, and protein in the same model, carbohydrate remained significantly associated with MCI or dementia (highest vs lowest intake: HR, 3.68; 95% CI, 1.61 – 8.38; P for trend = .01). In this model, fat and protein no longer showed a significant trend.
There were no significant interactions of percent carbohydrate, fat, or protein in the diet with age, sex, apolipoprotein E (APOE) ε4 allele, or body mass index.
The researchers also found trends toward reduced MCI with higher monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) intake. "High intake of fish, an important source of omega 3 PUFA, has been associated with a reduced risk of cognitive impairment in elderly persons," they note.
In several studies, dietary patterns have been associated with late-life cognitive function. High intake of fruits, vegetables, a Mediterranean-style diet, and several micronutrients, including vitamins B, C, E, have been found to have beneficial effects. Some prior studies have linked a high caloric intake with increased risk for cognitive impairment and caloric restriction with reduced cerebral beta-amyloid burden.
Other data has shown a lower risk for incident Alzheimer’s disease (AD), MCI, and progression from MCI to AD in older adults who adhered more to a Mediterranean-style diet, characterized by a high intake of omega-3-rich fish.
Dr. Roberts and colleagues note that their findings provide some of the first data on the influence of macronutrients in the diet and 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 MCI."
J Alzheimers Dis. Published online October 2012.