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An analysis of Vanderbilt Memory and Aging Project study data found that a high-fat diet was associated with a faster reduction in temporal lobe volume in cognitively unimpaired participants. However, in individuals with mild cognitive impairment, adherence to the same type of diet was associated with a slower enlargement of the inferior lateral ventricle area of the brain. The paper was published in Alzheimer’s & Dementia.
As people age, their risk of developing dementia increases, although dementia is not an inevitable part of normal aging. Dementias are disorders involving progressive declines in memory, reasoning, language, judgment, or other cognitive abilities that interfere with daily life. The most common type of dementia is Alzheimer’s disease. This disease is associated with an abnormal accumulation of proteins called amyloid plaques and tau tangles in the brain.
Aside from Alzheimer’s disease, dementias also include vascular dementia (resulting from reduced blood flow or damage to brain tissues caused by strokes or small-vessel disease), Lewy body dementia, frontotemporal dementia, and others. The exact causes of dementias are not fully understood, but scientists believe that they are caused by a complex interaction between genetic predispositions and the environment. Up to 40% of the risk is attributable to modifiable lifestyle factors, including diet.
Lei Fan, a researcher at Vanderbilt University Medical Center, and colleagues examined whether dietary fat intake was associated with changes in gray matter atrophy rates detected using neuroimaging over time in older adults. They were also interested in interactions of these changes with cognitive status, their dependence on sex, and whether an individual is a carrier of the APOE ε4 gene variant. APOE ε4 is a gene variant that increases the risk of developing Alzheimer’s disease.
These researchers analyzed data from the Vanderbilt Memory and Aging Project. This is a longitudinal observational study that investigates vascular and neurological health and the aging of older individuals free of clinical dementia at enrollment. The data came from 758 participants of the Vanderbilt Memory and Aging Project Legacy Cohort and the Expansion Cohort. Their average age was 67 years. About 47% were men, and 35% were carriers of the APOE ε4 gene variant.
The Legacy Cohort recruitment began in September 2012, and all participants were required to be at least 60 years old, have adequate auditory and visual acuity, and have a reliable study partner. The Expansion Cohort recruited individuals aged 50 years or older and recruitment started in August 2021.
Depending on their assessed cognitive status, participants were categorized as either cognitively unimpaired or mildly cognitively impaired. Participants completed magnetic resonance imaging of their brains at enrollment in the study and on at least one more occasion. They also completed a questionnaire called the Quick Food Scan fat screener, allowing study authors to estimate their total dietary fat intake. Data were collected at the start of the study, 18 months later, and then 3, 5, 7, and 9 years after the start of the study.
Results showed that, cross-sectionally at baseline, neither total fat intake nor the percentage of energy derived from fats was associated with the total volume of the brain’s gray matter or with the volumes of specific lobes of the brain. However, longitudinally over an average of 4.6 years, individuals deriving a higher percentage of their energy from fats tended to show a slower rate of enlargement of the interior lateral ventricle volume. This association was weak, and it disappeared when study authors corrected their detection thresholds for multiple comparisons.
Further analysis showed that the percentage of energy derived from fat was associated with a faster reduction in temporal lobe volume in cognitively unimpaired participants. In contrast, in individuals with mild cognitive impairment, a higher percentage of energy derived from fat was associated with slower enlargement of the inferior lateral ventricle region of the brain.
The temporal lobe is a region of the brain that supports memory and language. The inferior lateral ventricles are spaces filled with fluids near the temporal lobe. Their enlargement reflects the loss of brain tissue in surrounding areas.
“A high-fat diet is associated with accelerated gray matter atrophy, particularly in [Alzheimer’s disease-relevant] regions such as the temporal lobe, in [cognitively unimpaired] adults, but is associated with slower atrophy in individuals with existing [mild cognitive impairment], which is mainly driven by APOE ε4 carriers and/or female individuals,” the study authors concluded.
“Different mechanisms may be involved in the fat–neurodegeneration relationship across cognitive statuses. Halted atrophy associated with a high-fat diet, observed exclusively in individuals with existing [mild cognitive impairment], may reflect the role of fat as part of a compensatory mechanism in response to progressive [Alzheimer’s disease] pathology and metabolic challenges.”
The study contributes to the scientific understanding of the links between diet and mental health. However, it should be noted that the design of this study does not allow any causal inferences to be derived from the results. It is also limited by the fact that the cohort was predominantly white, well-educated, and relatively healthy. Additionally, a single self-reported dietary fat assessment at baseline may not reflect long-term variations in dietary intake.
The paper, “High-fat diet is associated with accelerated gray matter atrophy in cognitively unimpaired older adults but slower atrophy in individuals with existing mild cognitive impairment,” was authored by Lei Fan, Yunyi Sun, Dandan Liu, W. Hudson Robb, Kimberly R. Pechman, Niranjana Shashikumar, Yukti Vyas, Bennett A. Landman, Timothy J. Hohman, and Angela L. Jefferson.