Obesity and Alzheimer’s linked through early metabolic disruptions

By 2030, the population in the United States aged 65 and older is expected to reach 71 million or about 20% of Americans. This growth is likely to increase the burden of age-related diseases, particularly Alzheimer's disease (AD), affecting about 1 in 9 adults over 65.

At the same time, obesity has become increasingly common, including among older adults, where prevalence has nearly doubled in recent decades. Obesity is a major risk factor for metabolic disease, and growing evidence now links it to brain health and dementia risk.

A review from Florida Atlantic University, published in the journal Cells, examines the growing biological links between obesity and AD, highlighting how disruptions in metabolism can influence brain health. It explores the complex pathways through which adipose tissue and whole-body metabolism interact with the central nervous system, shedding light on how these processes may contribute to neurodegeneration and cognitive decline.

The authors synthesize evidence showing that obesity and AD share overlapping metabolic disturbances that arise early in disease progression – often well before clear clinical symptoms appear.

Obesity and Alzheimer's disease are closely connected through the way the body's metabolism works. Both conditions involve similar problems in how fat tissue sends signals, how the body uses insulin and how cells produce energy. Of these, problems in the mitochondria – the cell's energy-producing structures – appear to be the most important. When mitochondria don't work properly, it disrupts energy supply throughout the body and brain, which can contribute directly to brain cell damage and the development of Alzheimer's disease."

Shailaja Allani, Ph.D., senior author, director of the Center for Molecular Biology and Biotechnology and associate scientist in the Department of Chemistry and Biochemistry within FAU's Charles E. Schmidt College of Science

Mechanistically, the authors explain that both obesity and AD involve breakdowns in the cell's main energy systems. Specifically, two key processes inside mitochondria – the tricarboxylic acid cycle and the electron transport chain – do not function properly. When these systems are impaired, cells produce less energy and generate higher levels of harmful molecules called reactive oxygen species.

This imbalance creates a state of "energy stress" and oxidative damage, meaning that important parts of the cell such as proteins, lipids and DNA begin to break down. In the brain, this damage contributes to hallmark features of AD, including the buildup of amyloid-β and abnormal changes in tau proteins.

At the same time, Allani and Romina María Uranga, Ph.D., co-author and an assistant professor of biochemistry at New College, note that obesity adds another layer of risk through disrupted signaling from fat tissue. Fat cells normally send hormones that help regulate metabolism, but in obesity these signals become unbalanced. Combined with chronic, low-grade inflammation throughout the body, this further disrupts communication between the body and brain, increasing vulnerability to neurodegeneration.

"An important implication of our findings is that these metabolic changes don't just appear once disease is established – they likely begin much earlier," said Allani. "In fact, they may help drive the development of disease before symptoms show up. This makes them potential early warning markers that could help identify individuals at risk. Rather than being late effects of Alzheimer's or obesity, we increasingly see these metabolic disruptions as early, upstream changes that set disease processes in motion."

From a translational standpoint, the review highlights mitochondrial function and restoration of gut-brain axis balance as promising targets to help prevent or delay both metabolic and neurodegenerative diseases.

The gut microbiota plays a central role in brain health by shaping metabolism, inflammation and mitochondrial activity. In a balanced state, it supports immune function and produces beneficial compounds such as short-chain fatty acids that help protect neurons and may lower AD risk. When disrupted, however, increased gut permeability allows inflammatory molecules to enter the bloodstream – fueling brain inflammation, oxidative stress, amyloid and tau pathology, and ultimately neuronal damage, all hallmarks of neurodegeneration.

"Diet, aging, obesity and stress strongly influence core metabolic processes, and unhealthy patterns are linked to higher dementia risk," said Allani. "While animal studies show strong causal effects, human results are more variable – but together, the evidence suggests these metabolic processes play an important role in driving Alzheimer's and cognitive decline."

The authors note that the mechanistic links described, while well-supported by current evidence, require further validation in clinical settings.

Looking ahead, this integrated view of obesity and AD shifts attention toward earlier detection and whole-body prevention. The review suggests that monitoring metabolic health could identify risk long before symptoms appear, opening the door to earlier and more effective intervention.

It also highlights therapies that act on the body as a whole rather than the brain alone, including improving insulin sensitivity, reducing oxidative stress and regulating adipokines – chemical signals released by fat cells that help control metabolism, hunger and inflammation.

"What emerges from this research is a shift in perspective – from treating obesity and Alzheimer's as separate conditions to understanding them as interconnected processes rooted in metabolic health," said Allani. "This opens the door to earlier, more comprehensive interventions that target the underlying biology shared by both diseases, rather than responding only after damage has already occurred."