Does your brain shrink as your belly grows? The answer, sadly, is “Yes”.

Our beloved Western Diet, loaded with fat and added sugar, makes us gain weight, changes our risk of cardiovascular and metabolic disease, and alters the structure and function of our brains. Read the related post “Western Diet Makes You Stupid.”

We’ll take a closer look at the evidence showing that obesity makes the brain shrink. The scientific term for brain shrinkage is atrophy. The post title was drawn from an article by Willette and Kapogiannis (2015). The post image comes from Pixabay For definitions, follow the link.

Brain Imaging Techniques

Only when computerized tomography or CT scanning was introduced could we seek answers to the question of whether overeating the Western Diet caused brain shrinkage. Computerized tomography was nothing short of a medical miracle. Researchers could look inside the skulls of living patients, and doctors could determine if stress or a disease such as tumor or stroke was causing our headaches.

Now we could examine the whole brain or sections of the brain. Beyond static pictures of brain structures provided by imaging techniques such as the MRI or CT, researchers could look at the brain at work. The PET scanner let us watch the brain absorb glucose or insulin in real time.

Modern Techniques

To learn more about the modern techniques used to study the brain, watch this video produced by the Khan Academy.

Brain Volume and Morphometry

To answer the question of whether the brain is shrinking in response to our eating behavior, we must measure its size (or volume) and its shape, both within and without. Morphometry is the measurement of the form of an object, and there are a number of mathematical techniques for measuring brain morphometry. This writer doesn’t pretend to understand them; but if you want to tackle these topics, start with a paper on the morphometric assessment of Alzheimer’s disease by Fjell & Walhovd (2011).

Gray Versus White Matter

A coronal black and white MRI scan of a healthy brain. The gray and white matter as well as the corpus callosum can be seen.

The brain is grossly divided into two distinct regions—white and gray matter. The gray and white matter regions are easily seen on an MRI.

The Neuron: Building Block of the Brain

Illustration of neuron showing the cell body, dendrites, and axon. From Pixabay

The body of the nerve cells make up gray matter (top left). The axon or connective part of the nerve cell is white matter (bottom right).

Brain Cells Don’t Regenerate

Unlike many other cell types in our bodies, nerve cells aren’t replaced. If you kill off a brain cell, it’s gone. If you lose enough brain cells because the health of your brain has been compromised, the brain shrinks. This cell loss can be seen as reduced volume in an MRI. Contrast this with a skin cell. If you cut your finger, the skin cells are replaced.

For an introduction to white and gray matter, watch the Khan Academy video. The Khan Academy is a great resource for reliable information presented in a clear and concise fashion.

The most important part of brain gray matter is the cell body of the neuron, and the neuron’s cell body contains the machinery, such as the nucleus and the mitochondria, which make it possible for the nerve cells or neurons to do their work. White matter (primarily axons), on the other hand, connects the brain cells with other parts of the brain and the body.

The Brain Is About Connections

Much like a society, brain cells must work together to accomplish anything, so there must be a complex interplay between multiple areas of the brain. If the brain shrinks and if white matter disappears due to loss of nerve cell integrity, our ability to act or think declines. We think more slowly, we can’t remember, or we get confused. We become demented.

For example, if the corpus callosum loses nerve cells and is smaller, the two sides of the brain are less able to communicate. The corpus callosum is the large nerve fiber bundle at the middle of the black and white MRI scan. The measurement of the volume of white versus gray matter is central to our understanding of how obesity, and by extension the Western Diet, changes the structure of our brains.

Thinning of Cortex in Alzheimer’s Disease

We’ll use the thinning of the outer mantle or cortex of the brain caused by Alzheimer’s disease to illustrate some important features of cortical thinning as indexed by brain imaging techniques. For a definition of cortical thickness, follow the link.

Alzheimer’s dementia is well known to most of us. In the figure, the MRIs (Magnetic Resonance Imaging) of individuals with normal brains, those with mild cognitive problems (MCI), and those diagnosed with Alzheimer’s Disease (AD) are compared. The black lines point to the normal brain data. Note that the basic MRI data have been transformed to make the changes clear.

From the research of Fjell and Wallhovd (2011). Image shows the thinning of cortex in people with mild cognitive impairment and Alzheimer's dementia.

What We Know

  • The structural changes in the brain caused by Alzheimer’s disease can be measured by an MRI.
  • For dementia patients, the surface of the brain is thinner and smoother due to loss of ridges (gyri) and brain cells. In other words, the brain shrinks (third image from left).
  • The MRI-based quantification of brain morphometry detects smaller changes in mental ability such as Mild Cognitive Impairment (MCI). Note the thinning of cortex in MCI patients (image to far left).
  • The thinning of the cortex reflects the amount of mental ability lost (more for Alzheimer’s dementia than mild cognitive impairment).

Obesity and Dementia: Actuarial Bad News

Picture of my Aunt Caroline at a family picnic. I can't remember her doing anything other than eating or getting ready to eat.

If you’re obese, your chance of becoming demented is increased by 35%.

Picture of one of my obese aunts doing her favorite thing.

Obesity Attacks Many Higher Brain Areas

If you are obese or overweight, the health of the neurons or nerve cells in your brain suffers. Watch the “How to read an MRI of the brain for a tour of a clinical MRI examination.

Examine the MRI scans of overweight persons (Raji et al., 2010) Below there are three views of the brain. The view on the left shows the brain cut in half from top to bottom (sagital). The middle view is a section of the brain cut from ear to ear (coronal). The view to the right is a slice from the forehead to the back of the head (axial).

Enhanced MRI scans from Raji et al. (2010) showing areas of reduced brain volume in three views.

The brain areas highlighted in blue are significantly smaller in obese and overweight people. The areas of greatest loss or brain shrinkage are orbital frontal cortex (red arrow), hippocampus (yellow arrows), and midbrain (white asterisks = putamen, globus pallidus, thalamus). Many brain areas are spared. Obesity doesn’t change the volume of a sensory cortex such as the occipital cortex (vision). Look at the left image. The occipital cortex is in the middle of the rear of the brain, and it is highlighted in yellow/gold (Raji et al., 2010).

Being Either Over or Underweight Is Bad for the Brain

The bar graph shows the prevalence of dementia between the ages of 65 and 90+ for underweight (blue bars), overweight (orange bars), normal weight (green bars) and obese people (red bars) (Iozzo & Guzzardi, 2019).

Bar chart showing the prevalence of dementia for underweight, overweight, normal weight people across the senior years. From Iozzo and Guzzardi (2019)

This graph shows us four things:

  • The rate of dementia caused by carrying too many pounds gets worse as our age advances. Compare the 65-69 year old age group with the 85-89 age group (red bars).
  • Being classified as overweight is nearly as dangerous as being called obese (orange vs. red bars).
  • For the elderly, low body weight is also associated with dementia (blue bars).
  • People of normal weight can also become demented but at a significantly lower rate (green bars).

This Research Makes Me Uncomfortable

These research findings are scary. You may be tempted to dismiss them for a variety of reasons. We’ll examine some of these one by one.

  • I’m not overweight enough to worry.
  • I’m too young to worry, so I’ll worry about that when I’m old.
  • The lost brain volume doesn’t change my ability to get an education, do my job, or manage my day to day life.
  • It’s hopeless so I might as well eat what I like for as long as I can.

I’m Not Fat, I’m Fluffy

When I was carrying more weight than I wanted, seeing someone heavier than me was vaguely reassuring. Now, I know being fluffy put the health of my brain at risk.

In apparently healthy elderly who weren’t showing signs of dementia, researchers were surprised to find decreased white and gray matter volumes in some subjects. These subjects weren’t complaining of memory or mental problems. Why were they losing brain cells?

When all the possible contributing factors were eliminated, one variable survived. That variable was body mass index or BMI (Raji et al., 2010). These people weren’t losing brain cells because they had heart disease or diabetes. Their brains were shrinking because they had too much fat in their bodies– the more body fat, the greater the loss of brain tissue.

More than 4% of brain volume is lost for every standard deviation gain in BMI.

(Raji et al., 2010)

The Scarlet O’Hara Approach to Obesity

Gone with the Wind photograph of Vivian Leigh as Scarlet O'Hara. Scarlet is reclining on a mound of pillows.

“I’ll think about it tomorrow.”

The Scarlet O’Hara Approach Won’t Work

You mustn’t put dealing with your expanding belly off until tomorrow. Being overweight or obese isn’t something for grandpa and grandma to worry about. Being overweight plays no favorites when it comes to brain health. Obesity damages the brains of our children, youth, middle aged, and elderly (Iozzo & Guzzardi, 2019). The troubling and serious issue of childhood obesity is tackled in another post.

Being obese or overweight reduces the density of gray matter in many areas of the brain including prefrontal cortex, somatosensory cortex, temporal cortex, cerebellum, and subcortex as indexed by the MRI (Buie, Watson, Smith, & Sims-Robinson, 2019; Hassenstab et al., 2012, Iozzo & Guzzardi, 2019; Willette & Kapogiannis, 2015).

Thinning of the Temporal Cortex in Young Adults

If you think you’re too young and I can’t be talking to you, look at the brain volumes and health of the youngest adult samples of obese, overweight, and lean young adults (average age = 29) (Veit et al., 2014).

If you’re young but obese or overweight, the thickness of your cortex is reduced. Using very sensitive measures, the amount of fat in the body is related to nerve cell loss of the temporal cortex—the more fat, the greater the loss (Veit et al., 2014)

Thinning of temporal cortex in a). Other areas are affected in middle age b).

In a study of young Japanese males, being overweight or obese decreased the volumes of the medial temporal lobes, hippocampus, and precuneus. A recent MRI spectrography study revealed metabolic abnormalities in frontal lobe gray matter and white matter in a group of younger obese persons (Iozzo & Guzzardi, 2019).

Old picture of Aesop's fable about fate of the ant and the grasshopper. The grasshoppers in fancy dress want to gain entrance into the ant's food stores as winter approaches. You can't put things off!

You’d rather be a grasshopper and party today. Image from the Library of Congress

What About the Long Haul?

So you’re still skeptical. Maybe the researchers just looked at  groups of outliers. What happens if you follow a group of people of different sizes and shapes for forty years?

That’s what Franz and colleagues wanted to know, so they collected weight, health, and MRI brain scan data from 373 Vietnam era twins beginning in their 20’s (Franz et al., 2019). When lean and obese people were compared, those who were fatter had a different brain health trajectory. Their cortices were thinner in many areas of the frontal and temporal cortex. Their mental abilities were more likely to be compromised.

Excess BMI at midlife suggests the potential for increased risk of cognitive decline later in life.

Franz et al., 2019

I’m Overweight and I’m not Stupid!

Picture of actress Melissa McCarthy. She has struggled with her weight and has gained and lost weight many times.

Melissa McCarthy has worn every clothing size from 6 to 22.

You may want to reject this research because you look at your own life and you look at all the overweight people you know or see. There are many, many talented people who are overweight and very accomplished. Look at Melissa McCarthy, a brighter funnier person can’t be imagined.

You’re right and you’re wrong. You aren’t stupid, but being overweight is using up your brain cells.

Why Overweight People Stay Smart

Overweight people stay smart because their brains are using up precious resources to compensate for the metabolic overload caused by too much fat in the body.

Brain glucose uptake by age fron Guzzardi, 2019.

Iozzo and Guzzardi (2019) summarized the PET FDG data for glucose uptake in the brain. The figure shows the different brain utilization patterns for glucose at different ages. If you follow, the green line for normal weight what you see is a high rate of glucose need in the brain during the first few years of life as the brain goes through its growth spurt. The level of glucose needed by the brain then steadily decreases as we age.

Follow the path for obese people with cognitive losses (black circles). What you see is a heightened brain glucose uptake throughout life. The last trend line is for normal weight people with dementing conditions (white circles). Note the very low glucose uptake for older people with dementing conditions.

The Brain Wears Out

Forcing the brain to keep up with our excessive sugar and carbohydrate consumption by calling other brain regions into play and revving up the brain metabolism makes our brains shrink. Brain cells die. As the brain cells die, the metabolic needs of the brain change. The brain doesn’t have to feed as many cells. When we become demented, the brain isn’t doing much because our irreplaceable brains cells are gone forever. In the figure below, I’ve plotted this idea to make the point clear. This isn’t real data. I just made up the numbers to give you a visual impression. Follow the blue line.

Chart by L. J. Gummow to demonstrate that overtaxing the brain eventually leads to decreased brain metabolism and neuronal death.
Hypothetical Data: Illustrative Only! L. J. Gummow

Using Up Your Capital Brain Resources

I want you to see the cells in your brain as your mental capital, as a balance in Nature’s checking account. Nature endowed you with a finite number of brain cells. These cells will be with you, your companions, for the rest of your life.

You choose how to spend your brain cells. You can poison them with toxic gases. You can drown them in alcohol or drugs. You can kill them by running your motorcycle into a telephone pole and severing your spinal cord. You can damage or destroy them by overeating. Or you can feed them and treat them well. It is my fondest wish that you choose the latter.

Isn’t There Any Good News?

Yes, there is room for hope, but that’s the topic of another post.


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Linda J. Gummow

Linda J. Gummow

L. J. Gummow, Ph.D. and Robert E. Conger, Ph.D. are Clinical Psychologists. L. J. lost 25% of her body weight by following by reducing carbohydrates. In the process, she learned that much of what we're taught about weight loss is wrong. She and her co-author researched weight loss diets and the results show that sugar consumption is our public health enemy number one. R. E.

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