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Deeper Dive: Evaluating the results of an exploratory trial on diet and Alzheimer’s disease biomarkers in older people

This exploratory study found evidence suggesting that a Mediterranean-style diet improves Alzheimer’s biomarkers in people with normal cognition. But its results in people with mild cognitive impairment were counterintuitive.

Study under review: Mediterranean and Western diet effects on Alzheimer’s disease biomarkers, cerebral perfusion, and cognition in mid-life: A randomized trial

Introduction

Alzheimer’s disease[1] (AD) is a slow and progressive neurodegenerative disease that is a major cause of dementia (impaired reasoning and memory). As shown in Figure 1, it is characterized by plaques and tangles in brain tissue that are made up of the mysterious amyloid-beta (Aβ) and tau proteins, respectively. Although there are a number of hypotheses[2] that may explain the pathogenesis of AD, the overproduction, reduced clearance, and aggregation of these proteins is thought to be a major contributor to neurotoxicity and reduced neural connectivity. Moreover, their presence in cerebrospinal fluid (CSF) serve as prominent biomarkers of AD[3].

Figure 1: Tau and Aβ distribution, plaques, and tangles in AD

Adapted from: Busche et al. Nat Neurosci. 2020 Oct. [4], Silbert. Neurology. 2007 Aug. [5] 

The “Western diet[6],” characterized by high saturated fat, simple carbohydrates, and sodium, is associated with various cardiometabolic diseases (e.g., obesity, diabetes, cardiovascular disease) that may accelerate brain aging[7]. Cerebral perfusion, a measure of the passage of blood through the brain, has been inversely associated with obesity[8], diabetes[9], and cardiovascular risk factors[10], as well as AD[11] and accelerated cognitive decline[12]. When the supply of energy and blood throughout the body is disrupted, the brain is bound to suffer some consequences.

Nutrition[13] can seemingly have a substantial effect on the progression of neurodegenerative diseases. A handful of intervention trials[14] have demonstrated an inverse association between diets low in saturated fat and simple carbohydrates, such as the Mediterranean diet[15], and AD risk in elderly participants (older than 65). However, the effects of such diets on AD risk has been less explored in middle-aged people. This led the authors of the study under review to conduct a randomized controlled trial to determine whether changes in diet during midlife (45–65 years old) can influence biomarkers of AD risk and metabolic health.

Dietary interventions low in saturated fat, simple carbohydrates, and sodium, such as the Mediterranean diet, are inversely associated with cardiometabolic diseases and prominent biomarkers of AD in elderly participants. The authors of the study under review conducted a randomized controlled trial to determine whether changes in diet during midlife can influence biomarkers of AD risk and metabolic health.

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Other Articles in Issue #83 (September 2021)