Dr. David Perlmutter is a board-certified neurologist and seven-time New York Times bestselling author. He serves on the editorial board of the Journal for Alzheimer’s Disease and has published extensively in peer-reviewed scientific journals, including Archives of Neurology, Neurosurgery and The Journal of Applied Nutrition.

Perlmutter received his medical degree from the University of Miami Miller School of Medicine, where he serves as an associate professor. He lectures at major medical symposia, including ones sponsored by the World Bank, International Monetary Fund, Columbia University, Scripps Institute, New York University and Harvard University. His latest book is Brain Defenders : Harness the Power of Your Immune Cells to Protect Your Brain for Life.

 

What inspired you to write Brain Defenders and how does it expand on your previous work? 

What inspired me was the realization that metabolism profoundly influences immunity, and that this relationship explains so much about why a healthy brain begins to deteriorate. The brain’s immune cells can either protect and repair the brain or contribute to inflammation and degeneration, and their behavior is strongly influenced by our metabolic health, over which we have significant control. Once I understood how these pieces fit together, I knew this was something that needed to be widely shared.

My previous books explored how nutrition, blood sugar, the microbiome and lifestyle influence the brain. Brain Defenders brings these ideas together through the emerging science of immunometabolism—the relationship between the immune system and metabolism. It explains not simply what damages the brain, but how the brain’s own defenders can become destructive, and, importantly, what we can do to restore their protective function.

 

What are we currently getting wrong about Alzheimer’s disease?

We continue to treat Alzheimer’s as though it begins when memory fails. This idea is categorically wrong. In reality, the disease may have been developing for decades prior to the appearance of cognitive manifestations. We have also focused overwhelmingly on amyloid [an abnormal protein buildup that forms sticky deposits or plaques in the brain], treating it as the cause when it may be, at least in part, a downstream response to metabolic dysfunction, inflammation, infection and impaired cellular housekeeping.

 

Which recent studies most influenced Brain Defenders?

Several well-publicized interventional trials have demonstrated that a compilation of lifestyle interventions can protect cognitive function. The 2024 clinical trial led by Dr. Dean Ornish showed that intensive lifestyle intervention may benefit people with mild cognitive impairment or early Alzheimer’s. A recent Cochrane analysis of anti-amyloid antibodies underscored the gap between removing amyloid and producing a meaningful clinical benefit, while also documenting important risks in around 20 to 25 percent of patients. We can do better. The larger message is that Alzheimer’s is not driven by one pathway. It demands a broader, upstream approach.

 

Is Alzheimer’s a neurodegenerative disorder or an autoimmune disease?

Alzheimer’s is unquestionably classified as a neurodegenerative disease, but immune dysfunction plays a central role in how it develops and progresses. I would not call it a classic autoimmune disease in the way we describe multiple sclerosis or rheumatoid arthritis. Rather, it is a disorder in which the brain’s innate immune system becomes chronically activated and begins damaging the tissue it is meant to protect.

Microglia [immune cells in the brain and spinal cord] may lose the ability to clear debris, support neurons and maintain synapses. Instead, they can promote inflammation, excessive synaptic destruction and damage to brain neurons. So Alzheimer’s is neurodegeneration, but it is neurodegeneration profoundly shaped by immune dysregulation.

 

What is the key principle in Brain Defenders with respect to the treatment of Alzheimer’s?

The central principle is that we must move upstream. Instead of waiting for things like amyloid, tau [protein in the brain] and neuronal loss to accumulate and then trying to remove one of those downstream manifestations, we should identify and address the factors that caused the brain’s immune system to become dysfunctional in the first place. Benjamin Franklin reminded us that “an ounce of prevention is worth a pound of cure.”

That means improving metabolic health, reducing insulin resistance, supporting mitochondrial function, restoring the gut microbiome, improving sleep, treating vascular risk factors, reducing exposure to toxins, and maintaining physical and social activity. The goal is not simply to attack a pathological protein—it is to change the biological environment in which the disease is developing.

 

How can microglia become dangerous?

Microglia are the brain’s resident immune cells. They are constantly surveying their environment, looking for infection, injury, damaged cells and unwanted material. In their protective role, they clear debris, support repair, maintain synapses and help keep the brain resilient.

But when microglia are exposed chronically to signals associated with insulin resistance, poor diet, disrupted sleep, infection, toxins or a damaged gut barrier, they can remain locked in an inflammatory state. Instead of briefly responding to danger and then returning to a restorative mode, they continue releasing inflammatory chemicals and may begin eliminating healthy synapses. Obviously, this plays out badly for the brain. In other words, the brain’s defenders can become part of the problem, but their behavior is not necessarily fixed.

 

How does metabolism control brain immunity?

Every immune response requires energy. Microglia must continually decide whether to use their resources for surveillance and repair or for an aggressive inflammatory response. Their mitochondria and metabolic pathways help determine which program they adopt.

When metabolism is healthy, microglia are better able to respond appropriately and then resolve inflammation. But insulin resistance, elevated blood sugar, mitochondrial dysfunction and an oversupply of unhealthy metabolic signals can keep these cells in a defensive, inflammatory state. This is why metabolic dysfunction is not merely associated with Alzheimer’s disease; it is one of the fundamental forces actively shaping brain immunity and accelerating degeneration.

 

What is the role of the gut microbiome with respect to brain health?

The gut microbiome is intimately involved in regulating inflammation, metabolism, immune function and the integrity of the gut barrier. Gut bacteria produce compounds, including short-chain fatty acids, that communicate with the immune system and influence the brain’s microglia.

When the microbiome is diverse and well nourished, it helps maintain immune balance. When it is disrupted by a poor diet, antibiotics, environmental exposures or a lack of dietary fiber, the gut barrier may become more permeable. Bacterial products can then enter the circulation and promote systemic inflammation, which ultimately pushes the microglia to their destructive state. The gut and brain are not separate biological worlds. They are in constant communication.

 

What strategies can people use to protect their brain?

Begin with metabolic health. Know your fasting glucose, hemoglobin A1c, blood pressure, waist circumference, triglycerides, insulin level and other markers of cardiovascular risk. Exercise regularly, combining aerobic activity with resistance training. Prioritize restorative sleep and evaluate possible sleep apnea.

Eat a fiber-rich, minimally processed diet; protect the microbiome; maintain meaningful social relationships; continue learning; protect your hearing; avoid smoking; and minimize exposure to air pollution and other toxins whenever possible.

No single intervention guarantees protection. The power comes from addressing several interconnected pathways consistently over time. The encouraging message is that many of the factors influencing brain aging are within our reach.

 

What dietary modifications do you recommend?

I recommend a diet centered on whole, minimally processed foods, with abundant colorful vegetables, nuts, seeds, herbs, spices, healthy fats and adequate protein. Dietary fiber is especially important because it nourishes beneficial gut bacteria and supports the production of compounds that help regulate inflammation. That means a more plant-based diet.

Extra virgin olive oil, omega-3-rich fish, and other sources of unsaturated fat should generally replace refined carbohydrates and industrially processed foods. Added sugars and rapidly digestible carbohydrates should be reduced, especially in people with insulin resistance. The best dietary pattern is not defined simply by calories. It is one that supports metabolic flexibility, the microbiome, mitochondrial function and long-term adherence.

 

Why is sleep so important for brain health?

Sleep is active maintenance for the brain. During deep sleep, the brain strengthens important memories, regulates hormones, restores metabolic balance and enhances the clearance of accumulated waste products. Poor sleep also increases insulin resistance and inflammation and can push microglia toward a more reactive state. Sleep apnea is particularly important because repeated drops in oxygen place enormous stress on the brain and cardiovascular system. It’s important to note that sleep is not time taken away from productivity. It is one of the most important biological investments we make in maintaining cognitive function.

 

What can people diagnosed with Alzheimer’s do?

A diagnosis should never be interpreted as a reason to abandon prevention-oriented strategies. Even after symptoms begin, we should identify and address insulin resistance, hypertension, sleep apnea, hearing loss, nutritional deficiencies, medication effects, depression, inactivity and social isolation. Exercise, diet, sleep, cognitive engagement and vascular risk management remain highly relevant.

Current medications may provide modest symptomatic benefit for some patients. The anti-amyloid antibodies lecanemab and donanemab can minimally slow measured decline in carefully selected people with early disease, but the average benefit is minimal, treatment is burdensome, and there are meaningful risks, including brain swelling and bleeding. These treatments deserve an individualized discussion, not exaggerated promises. Removing amyloid does not address the full biology of Alzheimer’s.

 

How have you personally implemented the principles in Brain Defenders?

Having watched my own father die from Alzheimer’s, I try to live these principles every day, although certainly not with perfection. Exercise is foundational for me, including both aerobic and resistance training. I pay close attention to metabolic health, prioritize sleep, eat a diet built around whole foods and fiber, and remain actively engaged intellectually and socially.

I also recognize that brain health is not solely about nutrition and exercise. Purpose, connection, time in nature, stress management and continuing to challenge ourselves all influence the biology of aging. The central question I ask is: Am I creating an environment that allows my brain’s protective systems to function as they were designed to function?

 

Was there a particular moment that drove home the importance of brain-defense strategies?

It was less one dramatic moment than a pattern I witnessed repeatedly over decades of caring for patients. People would come to me after substantial cognitive decline had already occurred, and the conversation was largely about managing a disease that had been developing silently for many years.

What was especially striking was how often these patients had long-standing metabolic dysfunction, poor sleep, vascular disease, inflammation or other identifiable risks. Yet no one had connected those issues to their future brain health. That experience convinced me that waiting for symptoms is a failed strategy. We need to begin defending the brain while it is still functioning well. As President Kennedy stated, “The time to repair the roof is when the sun is shining.”

 

What is the future of brain-health research and preventive care?

The future will be involved with earlier interventions before cognitive symptoms are evident, more personalized and more focused on mechanisms. Blood-based biomarkers such as phosphorylated tau may allow us to recognize biological changes years before dementia appears. Wearable technology and advanced metabolic testing will help us understand risk continuously rather than during an occasional office visit.

I also believe research will increasingly focus on the microglia, mitochondria, the microbiome, immune regulation and the restoration of resilience, not simply the removal of individual proteins. Preventive brain care should ultimately become as routine as monitoring blood pressure or cholesterol. We should not wait until cognition fails before becoming interested in the brain.

 

If readers could change just one daily habit, what would you recommend?

Move your body every day. Exercise improves insulin sensitivity, increases blood flow to the brain, supports mitochondrial function, promotes the production of brain-derived neurotrophic factor and helps regulate inflammation. It also improves sleep, mood, balance and cardiovascular health. Ideally, people should combine aerobic activity, resistance training and activities that challenge coordination. But the starting point can be simple: take a brisk walk, especially after a meal. Remember, there is no pill currently available that produces the broad range of brain-protective effects that regular physical activity provides.

 

What misconception about brain health do you hope this book will finally clear up?

The misconceptions I most want to challenge are that cognitive decline is an inevitable consequence of aging, and that our genes determine our destiny. Gene variants, such as APOE4, may influence risk, but they do not operate in isolation. Metabolism, inflammation, sleep, diet, exercise, environmental exposures and the microbiome all influence how that risk is expressed.

The brain is not simply waiting to deteriorate. It is responding continuously to the signals we send it. Brain Defenders is ultimately a book about agency: the recognition that we can absolutely begin changing many of those signals today.

 

Sandra Yeyati is national editor of Natural Awakenings.