A Review of Mechanistic Links Between Obesity and Alzheimer's Disease
Researchers have in recent years undertaken considerable effort to demonstrate that the biochemistry of obesity overlaps with the biochemistry of Alzheimer's disease. Setting aside motivations relating to linking two large pools of research funding (obesity researchers would love to be able to write Alzheimer's grants, and vice versa), it is certainly possible to point to a great many interesting findings in this context: circulating choline; microglial lipid accumulation; changes in extracellular vesicle profiles; links between visceral fat specifically and protein aggregation in the brain; the commonality of insulin resistance to both conditions; and so forth. From a cellular biochemistry point of view, it looks quite compelling.
Inconveniently, however, the epidemiological data from large study populations just doesn't support as direct a role for obesity in Alzheimer's risk as it does for, say, type 2 diabetes. Type 2 diabetes is very, very clearly a consequence of being overweight for the vast majority of patients, and losing that weight makes the condition go away. GLP-1 receptor agonists produce involuntary calorie restriction and weight loss, and have positive effects on patients with type 2 diabetes. So does voluntary calorie restriction achieved without the use of fancy modern drugs. GLP-1 receptor agonists do not slow the progression of Alzheimer's disease, however. To my eyes the question is more one of why so many obese people do not go on to develop Alzheimer's disease, particularly given the existence of so many plausible connecting mechanisms evaluated by the research community in recent years.
From Lipids to Mitochondria: Shared Metabolic Alterations in Obesity and Alzheimer's Disease
The number of individuals aged 65 and older will grow significantly over the next few years. This demographic shift is expected to increase the economic burden on society and, importantly, to elevate the prevalence of age-associated disorders such as Alzheimer's disease (AD), a neurodegenerative condition characterized by memory impairment and progressive cognitive decline. According to estimates from the Alzheimer's Society, 11% of individuals over the age of 65 in the U.S. are diagnosed with AD. At the same time, obesity - a chronic condition characterized by excessive fat accumulation and a major driver of metabolic disorders such as type 2 diabetes, liver disease, and cardiovascular disease - has risen markedly across the lifespan. Notably, its prevalence among older adults nearly doubled from 22% to 40% between 1988 and 2018.
Growing evidence indicates that obesity and AD are mechanistically linked through overlapping metabolic disturbances that contribute to structural and functional alterations in the brain and increase the risk of cognitive decline. Based on the evidence presented in this review, AD and obesity share convergent metabolic disturbances that often emerge early, preceding overt clinical manifestations. Key shared mechanisms include mitochondrial dysfunction, with coordinated impairments in the TCA cycle and electron transport chain leading to reduced adenosine triphosphate (ATP) production and excessive reactive oxygen species (ROS) generation; oxidative stress, which damages macromolecules and promotes pathological cascades such as amyloid-β aggregation and tau phosphorylation in the brain; dysregulation of adipokine signaling in adipose tissue; and systemic metabolic inflammation, linking peripheral energy imbalance to neurodegenerative vulnerability.
Given the concurrent rise in both conditions, elucidating their shared metabolic mechanisms has become increasingly important. This review focuses on the interplay between mitochondrial dysfunction, oxidative stress, and lipid dysregulation as converging mechanisms that connect peripheral metabolic imbalance to neurodegeneration. Furthermore, because adipose tissue functions as an endocrine organ, these systemic alterations can influence central nervous system (CNS) function. Accordingly, this review examines how adipose tissue dysfunction influences neurodegeneration, emphasizing the role of metabolic health in shaping cognitive decline.