What Sugar Really Does to Your Brain (and How Ozempic Fits In)

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What if I told you that eating a donut can do something to your brain that looks a lot like what cocaine does to it?

I know that sounds dramatic. But by the time you finish reading this, I think you’ll see it differently. Because the truth is that sugar isn’t just fattening, it’s actually toxic to your brain. Obesity can shrink your brain at any age. And the new class of weight-loss drugs everyone is talking about may be doing something in the brain that goes well beyond the number on the scale.

Let me walk you through what actually happens when you eat.

The Sugar Spike and the Crash That Follows

When you eat sugar, your blood glucose rises. Your pancreas responds by releasing insulin, a hormone that works like a key, unlocking your cells so glucose can get inside and be turned into energy.

The type of food matters enormously here. Complex carbohydrates like fruits and vegetables cause a slow, gentle rise in blood sugar. But a donut or a bowl of ice cream causes a sharp spike, which triggers a flood of insulin. That surge of insulin then pushes your blood sugar too low, and that crash is what leaves you hungry and craving sugar again an hour later.

Repeat that cycle day after day, and it often leads somewhere you don’t want to go: diabetes and obesity.

Three Ways This Cycle Quietly Damages Your Health

Over time, this pattern of sugar spikes and insulin surges causes three deeper problems.

First, your cells can become resistant to insulin. Sugar starts building up in your blood instead of getting inside your cells where it belongs. This is called insulin resistance, and it’s an early step toward metabolic syndrome and diabetes.

Second, excess sugar binds to proteins throughout your body in a process called glycation. Too much glycation impairs how those proteins function. This is part of why patients with poorly controlled diabetes can lose sensation in their toes, lose their vision, or damage their kidneys to the point of needing dialysis.

Third, high sugar levels generate free radicals and inflammation everywhere — throughout your body and inside your brain.

Why Sugar Is Toxic to Your Brain

This is where it gets personal for me as a neurologist.

In animal studies, high sugar levels reduce the number of dendrites, the branches on your neurons that receive connections from other neurons. Fewer connections mean less communication between brain cells, and that shows up in real life as brain fog and memory loss.

A high-sugar diet also reduces neurogenesis, the birth of new neurons in your hippocampus, which is your brain’s memory center. In other words, sugar makes it harder for your brain to build the very cells you rely on to learn and remember.

And in human studies, obesity is consistently linked to a smaller hippocampus and a higher risk of disease.

Brain Shrinkage Happens at Every Age

Here’s what surprises most people: this isn’t just a concern for older adults.

Brain atrophy linked to excess body fat shows up across every age group. Even children are not spared. When obesity affects a young brain, some of the academic struggles we see in kids may actually be tied to changes in the hippocampus and other brain regions.

There’s also a circulation piece to this story. In people with multiple risk factors, researchers have found lower blood flow throughout the brain, along with lower scores on memory and other brain functions. Less fuel reaching the brain means less capacity to think, focus, and remember.

Why We Eat and Why Willpower Isn’t the Whole Story

So why do we eat in the first place, and what actually controls our eating behavior?

Part of the answer is hormonal. Chemicals in your blood, leptin, insulin, and others, tell your brain when to stop eating, while ghrelin, the “hunger hormone,” tells your brain to eat more.

But eating isn’t only about hunger. Your brain’s reward system, the same circuitry involved in addiction, lights up when you eat, and especially when you eat sugar. Over time, this creates craving and tolerance. You crave sugar constantly, and you need more of it to feel the same satisfaction you once got from less.

Your prefrontal cortex is supposed to act as the brake on all of this, the part of your brain that helps you stop after the first bite. But in obesity, the prefrontal cortex doesn’t work as well, and your willpower around food shrinks along with it.

I want to be clear about what this means: eating too much is not simply a lack of discipline. For many people, it reflects a genuine addiction to food. That’s not an excuse; it’s a starting point for real solutions.

Where Ozempic Fits In

This brings us to the newest piece of the puzzle.

Medications like Ozempic work in three places at once. In the pancreas, they increase insulin and lower a hormone called glucagon. In the stomach, they slow digestion so you feel full faster and for longer. And in the brain, they reduce appetite directly, quieting the cravings that drive addictive eating.

Many patients on these drugs describe something fascinating: a quieting of what’s been called “food noise,” the constant mental chatter about food that runs in the background all day. Researchers are now studying whether these same medications might help with Alzheimer’s prevention, and even with addiction to alcohol, smoking, or other behaviors, since they appear to turn down the brain’s reward and addictive pathways.

But turning down the reward system isn’t free of trade-offs. Some patients report depression, fatigue, or even brain fog. This is still very much an active area of research, and I’ll be watching it closely.

What I Want You to Remember

Your brain is not separate from the food you eat. Every sugar spike and every extra pound leaves a mark on every organ in your body and on your brain.

If you want to stay sharp, the path is clear. Eat healthy food in reasonable portions. Exercise often. When you are fit, your brain simply works better.

People have known the essence of this for centuries: healthy body, healthy mind. What’s different now is that, for the first time, we have the scientific data to understand exactly how it works and how you can use that knowledge to take back control of your eating and protect your brain for decades to come.

Dr. Majid Fotuhi is a Harvard- and Johns Hopkins-trained neurologist, bestselling author of The Invincible Brain (USA TODAY Bestseller), and one of the world’s leading experts on brain health and cognitive performance. He has spent more than three decades studying the brain’s capacity for growth and repair. To discover your brain health score and receive a personalized 10-page report, take the free Invincible Brain Assessment at invincible.drfotuhi.com.

📺 Watch the full video on Dr. Fotuhi’s YouTube Channel.

Keep up with Dr. Fotuhi on LinkedIn & Instagram.

Why Exercise Is the Most Important Pillar of Brain Health

I want to talk to you about the single most important thing you can do for your brain.

In my work as a neurologist, I describe five pillars of brain health: fitness, sleep, nutrition, mindset, and brain training. Each of them matters. Each of them, done well, makes your brain measurably stronger. But they are not equal, and by far the most important pillar of brain health is exercise and fitness.

I know that “exercise is good for you” sounds like advice you have heard a thousand times. What most people have never heard is why, what actually happens inside your brain and your cells when you move your body. Once you understand the biology, exercise stops being a chore on your to-do list and becomes more like a superpower.

Let me walk you through it.

Tiny Factories Power Your Cells, and You Can Build More of Them

Inside every one of your cells are small structures called mitochondria. Think of them as tiny factories that generate ATP, the energy currency of your body. Everything you do requires ATP. Your brain runs on it. So does your heart, your kidneys, your muscles, your skin. Nothing in your body works without the energy these little factories produce.

Here is the part that should concern you: with aging, both the number and the function of your mitochondria decline with every decade of life. It is one of the quiet engines of aging, operating silently in the background, long before you feel any difference.

And here is the part that should excite you: exercise reverses that decline.

When you exercise, you increase the number of mitochondria inside your cells. More factories. More energy. More capacity in every organ of your body, including your brain. If you want to rejuvenate every cell in your body at the most fundamental level, this is how you do it. And the best way to build more mitochondria is to build your fitness stamina.

More Blood Vessels, More Oxygen, More Nutrition

The second thing exercise does is expand your brain’s supply lines.

Physical activity increases the number of capillaries, the small blood vessels that deliver blood throughout your brain, your retina, your skin, and every other organ. More vessels mean more blood flow. More blood flow means more oxygen and more nutrition reaching every cell in your body.

Your brain is one of the most metabolically demanding organs you have. It depends, moment to moment, on a rich and steady supply of oxygen and nutrients. When you exercise regularly, you are literally upgrading the infrastructure that feeds it.

Exercise Grows the Part of Your Brain That Remembers

The third effect is, to me, the most remarkable of all.

Deep inside your temporal lobe sits a structure roughly the size of your thumb called the hippocampus. It is the ground zero for learning and memory in your brain. And when you exercise, you increase the number of neurons and synapses inside your hippocampus.

Let that sink in. Physical movement, walking, swimming, dancing, and playing tennis, causes new brain cells and new connections to form in the exact region that determines how well you learn and remember.

The downstream benefits are exactly what you would expect. People who exercise have a larger hippocampus and a larger cortex. They have better memory. They sleep better and enjoy a better mood. They are far less likely to develop Alzheimer’s disease decades later and less likely to suffer heart attacks and strokes along the way.

There are very few things in medicine I would call a no-brainer. Exercise is one of them.

The One Number That Predicts Your Brain’s Future

So what does it actually mean to be “fit”?

Fitness means stamina and endurance. How many flights of stairs can you climb? How far can you walk without stopping? These everyday questions point to something we can measure precisely, a number called VO2 max.

VO2 max is the total amount of oxygen your body can consume at peak exercise, usually measured in milliliters of oxygen per minute per kilogram of body weight. It is the gold-standard measure of cardiovascular fitness and endurance.

And it turns out to be far more than a fitness statistic. People with a higher VO2 max have more mitochondria in their cells, a bigger hippocampus, and a far lower likelihood of developing Alzheimer’s disease. It is a remarkable measurement, a single number that can tell you, today, what is likely to happen to your brain in the future.

You can measure your VO2 max precisely at a gym or a doctor’s office. But there are also simple ways to estimate it: walk one or two miles, then record your time, your heart rate, and your weight, and calculate your approximate VO2 max. I strongly recommend that you measure it and use that number as your baseline. What gets measured gets improved.

How to Build Your Fitness: The Right Way

If you have not been active, the path forward is simpler than you think. Here is what I tell my patients:

Start slowly. Do not go from nothing to a lot in one week. Begin with walking, and increase the amount of exercise you do on a weekly basis. Gradual, consistent progress is what builds mitochondria and what prevents injury and burnout.

Be persistent and win the first step. Some mornings, you will wake up and not feel like going for a walk. Do not negotiate with that feeling. Just get up and go. Once you have put your shoes on and stepped outside, the rest is easy. The first step is the difficult part; everything after it takes care of itself.

Find the exercise you actually like. If you don’t enjoy the gym, don’t go to the gym, go for a walk. If you don’t like running, play tennis. If you don’t like tennis, take dancing lessons. Do something you genuinely enjoy, because the best exercise is the one you will still be doing three months from now. Remember: the more active you are, the more mitochondria you generate.

My Prescription

Exercise is the most important thing you can do for your brain, and you need to do it every day.

My recommendation is simple: remain active every single day. Walk 5,000 steps or more as much as you can. Get at least three hours of real exercise each week, and make sure it is something you enjoy.

Do this consistently, and you will be doing the best possible service for your brain and your body. You will live longer. And you will stay sharp well into your 80s and 90s.

📺 Watch the full video on Dr. Fotuhi’s YouTube Channel.

Keep up with Dr. Fotuhi on LinkedIn & Instagram.

How to Become a Brain SuperAger

Our understanding of what happens to the brain has changed completely in the past five to ten years. We are living through a major paradigm shift in how we view aging — and what we believe happens to the brain as we grow older.

The popular belief is that once you hit midlife, your memory fades, your thinking slows, and there is nothing you can do about it. Recent scientific discoveries, including my own research publications, tell a very different story.

I am a neurologist and a professor at Johns Hopkins with four decades of clinical and research experience in memory and Alzheimer’s disease. I want to introduce you to one of the most exciting concepts in modern medicine: becoming a Brain SuperAger.

What is a Brain SuperAger?

A Brain SuperAger is someone in their 80s or 90s who performs like a person 20 or 30 years younger.

My own grandmother was one. Even at 90, she loved volunteering in her community, joining her prayer groups, and reading books. She was vibrant and full of life until her very last days.

SuperAgers like my grandmother are not born special. Every day, they make choices that keep their brains healthy — and you can make those same choices, too. A person who exercises regularly, eats well, sleeps well, manages stress, and smiles often can remain strong and functional well into old age. Give your brain the right conditions, and it will thrive and grow. It will keep you sharp and vibrant for life. Neglect it, and it will shrink — bringing memory loss, confusion, and dementia.

The 10 ways we quietly shrink our brains

These are the most important ways we neglect the brain and cause it to shrink. Each one does its damage silently, in midlife, long before any symptoms appear.

Chronic stress. Elevated cortisol damages the hippocampus, the thumb-sized region critical for learning and memory. The more years of chronic stress, the more the hippocampus shrinks.
Poor diet. Highly processed foods and foods high in sugar impair brain function at a cellular level.
Sedentary lifestyle. Physical inactivity reduces blood flow to the brain and lets brain cells shrink and fade.
Poor sleep. During sleep, the brain literally cleans itself. Without it, toxic proteins such as amyloid accumulate and form plaques.
Social isolation. Loneliness is one of the most powerful predictors of cognitive decline.
Untreated depression or anxiety. These are not only mood disorders — over time, they physically shrink the brain.
Uncontrolled high blood pressure. Vascular damage quietly erodes brain tissue for years before any symptoms appear.
Obesity and metabolic syndrome. Insulin resistance in the brain is a key driver of memory loss and cognitive decline.
Hearing and vision loss. When the brain stops receiving adequate sensory input, it begins to shrink.
Low cognitive engagement. A brain that is not challenged is a brain that is not growing.

The good news is that every one of these factors can be addressed — often without medication — through better lifestyle choices. People who care for their brain every day, the same way they care for their skin, really do become SuperAgers.

What decades of research reveal

Researchers at Northwestern, Rush, Harvard, Johns Hopkins, and many other leading institutions have spent decades studying SuperAgers — people in their 80s who stay sharp and independent. What they found is remarkable.

These individuals carry no special genes. They have no special features. They have not discovered a secret supplement or a magic intervention. What they share is a pattern of healthy, consistent lifestyle habits maintained over decades. They exercise and stay active. They keep strong social connections. They sleep well. They eat diets rich in vegetables, healthy fats, and lean proteins. They keep learning — an instrument, a language, a curiosity about the world. Their brain MRIs show less atrophy and larger hippocampal volume than their peers. This is not anecdote. It is what science consistently shows across decades of research at the world’s leading universities.

Change how you think about aging

The most important step toward becoming a SuperAger is to change how you think about aging and the brain.

There is a deeply harmful narrative in our culture that cognitive decline is inevitable — that it simply happens, and nothing can be done. I have spent 40 years watching patients internalize that story and then unconsciously live it out. Do not accept that narrative.

If you are in your 50s, 60s, or 70s and feel you are not as sharp as you were a decade ago, that feeling is a signal, not a verdict. It is your brain telling you that something on the list of 10 factors needs attention. Go through them one by one and ask yourself honestly: Am I sleeping enough? Am I moving enough? Am I under chronic stress? Am I socially connected? Am I eating in a way that serves my brain?

Then begin to address whatever you find — on your own, with the guidance of my book The Invincible Brain, or with a health professional. Address those issues, and you will see a difference in your thinking within weeks. Your brain is far more adaptable than you believe. Neuroplasticity does not stop at 60 or 70; the capacity to grow, heal, and sharpen is present throughout your lifespan.

The 5 Pillars of Brain Health

Most of what I have described comes down to five pillars — the foundations of becoming a SuperAger.

Regular exercise. Just 30 minutes of walking, five days a week, increases the size of your hippocampus and boosts BDNF, the brain’s growth hormone.
Brain-healthy nutrition. A Mediterranean-style diet rich in olive oil, fish, leafy greens, nuts, and berries has been shown in multiple large studies to lower the risk of Alzheimer’s and slow cognitive decline.
Optimal sleep. Seven to eight hours of quality sleep each night lets the brain flush out toxic proteins. Sleep is not passive — it is active brain maintenance.
Stress reduction. Chronic stress is one of the fastest ways to age the brain. Mindfulness, social connection, time in nature, and regular exercise all protect and nourish it.
Cognitive engagement. Challenging the brain with novel, complex activities — a new skill, a hard problem, structured brain training — builds cognitive reserve and expands resilience.

These pillars work together. Strengthen one, and you tend to strengthen the others, and the cumulative effect over time is profound.

Becoming a SuperAger is not about perfection. It is about awareness, intention, and consistency. Your brain responds to how you treat it, and the choices you make today are quietly shaping the brain you will live with tomorrow. You do not have to accept cognitive decline as your destiny. You can aim, instead, to become a Brain SuperAger.

Watch the full video on Dr. Fotuhi’s YouTube Channel.

Keep up with Dr. Fotuhi on LinkedIn & Instagram.

How Your Brain Rewires Itself to Make You More Intelligent

By Dr. Majid Fotuhi, MD, PhD

Right now, while you’re reading this, something extraordinary is happening inside your head.

Each of the billions of neurons in your brain is connected to thousands of other neurons through contact points called synapses. As you pay attention to these words, your neurons are strengthening some of those synaptic connections and building new ones. New proteins are arriving and getting installed in the branches of your neurons. New synapses are being formed and remodeled in real time with no conscious effort from you whatsoever.

This process is called neuroplasticity. And once you truly understand it, it has the potential to change the way you see yourself — and what you believe you’re capable of.

Your Brain Is Not Fixed

For most of human history, scientists believed that the brain was essentially a static organ. You were born with a certain number of brain cells, and once adulthood arrived, the structure of your brain was largely set. Learning was possible, of course, but the underlying hardware was thought to be fixed.

We now know this is wrong.

Your brain is a living, dynamic, constantly changing structure. Every time you practice a new skill, neurons build new connections between different areas of your brain. The more you practice, the more those connections are refined and strengthened. Over time, what was once effortful becomes automatic — not because your personality or willpower changed, but because the physical architecture of your brain changed.

The more roads your brain builds, the faster and more efficiently information moves between different regions. And the result of that expanded network is something we call intelligence.

Intelligence Is Something You Build

This is one of the most important insights I’ve shared in my 35 years of studying the brain. Intelligence is not a fixed quantity you’re born with. It is the result of new synaptic connections forming between neurons.

Think of your brain like a city. When a city builds new streets, new highways, and upgrades its existing roads, communication between neighborhoods becomes faster and more efficient. Commerce increases. Ideas move more quickly. The city becomes more capable.

Your brain works the same way. Every new skill you practice, every subject you study, every challenge you push through, these experiences are literally building new roads inside your head. And those roads make you more intelligent.

This is not a metaphor. It is neuroscience.

What the Research Shows

The evidence for neuroplasticity is extensive and growing more robust with each decade of research.

One of the most cited studies examined London taxi drivers, who are required to memorize thousands of city streets before they can be licensed. Researchers found that these drivers had a measurably larger hippocampus — the brain region most critical for memory and spatial navigation — than non-drivers. The more years they had been driving, the more pronounced the difference.

Medical students provide another compelling example. Studies have shown that students who study intensively for three months in preparation for qualifying exams demonstrate measurable growth in hippocampal volume over that short window. When they stop studying after the exam, the growth levels off. The brain responds directly to the demands we place on it.

Musicians who begin practicing in childhood develop thicker connections between their left and right brain hemispheres than non-musicians. People who become fluent in a second language develop a more robust network of synaptic connections throughout the brain — and that additional cognitive reserve appears to protect them against cognitive decline decades later. Athletes who practice their sport extensively develop more elaborate and efficient neural networks for processing movement and spatial information.

Practice does not just build skills. It builds brains.

My Own Experience With Neuroplasticity

I did not always believe this about intelligence. Not because I hadn’t read the research, but because I hadn’t yet applied it to myself.

When I came to America in 1987, I had been accepted to Johns Hopkins for a doctoral degree in neuroscience. I should have been excited. Instead, I was frightened. I was trying to improve my English, adapt to an entirely new culture, and keep pace intellectually with some of the sharpest students in the country.

I remember sitting in an advanced neuroscience seminar, struggling to follow every word, and thinking: how on earth am I going to pass my qualifying exams?

I could not have imagined, sitting in that lecture hall, that I would one day become a neurologist and professor at the very institution that was intimidating me. I could not have imagined writing four books about the brain, one of which would become a USA TODAY bestseller.

The more I studied neuroplasticity, the more my confidence grew. The science showed me, again and again, that we all have the capacity to grow our brain — at any age, in any field. I had been underestimating my own neurons. And I had been wrong to do so.

What This Means for You

The most important thing I want you to take from this is simple: your brain has no limit for learning.

It does not matter how old you are. It does not matter how you performed in school. It does not matter whether you think of yourself as “a smart person” or not. These assessments were formed before you understood what your brain is actually capable of.

Every person who has ever mastered a new skill — learning a second language, becoming an exceptional athlete, developing expertise in a field they knew nothing about — started exactly where you are right now. Their brain was not different from yours. They simply gave their neurons the opportunity to build new roads and new connections. And those connections changed everything.

Your neurons know how to find each other. They know how to form new synapses. You do not need to teach them. You do not need to oversee the construction process. You just need to give them something worth building — and the patience to keep practicing.

Neuroplasticity does not stop at 25, or 40, or 60, or 80. It continues across your entire lifespan. I have seen it in my patients. I have seen it in my research. And I have lived it myself.

Every time you choose curiosity over comfort, every time you push yourself to learn something new, your neurons are reaching out and finding each other. Your brain is always waiting for you to give it that something new that’s worth building.

You really can become more intelligent — in any field you choose, at any age. The biology is on your side.

Dr. Majid Fotuhi is a Harvard- and Johns Hopkins-trained neurologist, bestselling author of The Invincible Brain (USA TODAY Bestseller), and one of the world’s leading experts on brain health and cognitive performance. He has spent more than three decades studying the brain’s capacity for growth and repair. To discover your brain health score and receive a personalized 10-page report, take the free Invincible Brain Assessment at invincible.drfotuhi.com.

Watch the full video on Dr. Fotuhi’s YouTube Channel.

Keep up with Dr. Fotuhi on LinkedIn & Instagram.

Dr.

Majid
Fotuhi

Dr.

Majid
Fotuhi