Your Brain Shrinks As Your Waistline Grows

Numerous studies have documented that as a person’s weight and BMI (body mass index) increases, their brain shrinks in size. Excess weight often leads to obesity and diabetes. These conditions destroy synapses, wither blood vessels in your brain, batter neural pathways, and kill neurons. The result is a smaller brain.

One study found that the brains of obese people looked 16 years older than their healthy counterparts while the brains of overweight people looked 8 years older. Researchers classified this as  ‘severe’ brain degeneration with serious implications for aging, including a heightened risk of Alzheimer’s.

What Is BMI and What’s Considered Healthy?

According to the National Institutes of Health, BMI is a measure of your body fat taking into account your height and weight. Go here for a handy BMI calculator, both metric and standard, or here for a BMI table. Generally, BMI categories are as follows:

Underweight = <18.5
Normal weight = 18.5–24.9
Overweight = 25–29.9
Obesity = BMI of 30 or greater

In addition to an estimate of body fat, BMI is a good gauge of your risk for diseases that can occur with more body fat. The higher your BMI, the higher your risk for certain diseases such as heart disease, high blood pressure, type 2 diabetes, gallstones, breathing problems, and certain cancers.

How Being Overweight Hurts Your Brain

In his book, Boost Your Brain: The New Art and Science Behind Enhanced Brain Performance, Majid Fotuhi M.D., Ph.D. explains:

In the brains of obese people, the loss of brain volume appeared to most affect certain parts of the brain: the frontal (attention) and temporal lobes (language), the hippocampus (memory), and the anterior cingulate gyrus (mood), for example. The relationship between global brain volume (the size of your brain) and BMI is linear, which means any excess body weight is associated with a slight reduction in brain volume…

One study found that participants with a higher BMI, a larger waist circumference, greater abdominal fat, and a bigger waist-to-hip ratio were more likely to have lower brain volume. Abdominal fat had the greatest correlation with reduced brain volume while waist-to-hip ratio was associated with a smaller hippocampus. Such changes translate into decreased cognitive performance and a greater risk of dementia.

The Link Between Being Overweight And Dementia

Many studies have tied being overweight with an increased risk of dementia. One long-term study tracking subjects over three decades found that obese subjects were at an 80% increased risk of developing dementia. Those people who had central obesity (weight around the stomach) were 3.6 times more likely than their non-overweight peers to develop dementia. That’s a 360% increased risk! Just being overweight had a 234% increased risk of dementia if the excess was primarily carried as belly fat.

Of course, being overweight does not mean that a person will get dementia or that a thin person is automatically smarter than their heavier counterpart. Everyone begins with different cognitive resources, and other factors have influence. In Boost Your Brain: The New Art and Science Behind Enhanced Brain Performance, Majid Fotuhi writes:

If you’re an obese college professor who plays the violin, exercises and belongs to a bird-watching club,you may be better off than a couch potato who weighs less but never exercises or explores his world. Still, it does mean  that the brains of overweight people aren’t in the best possible shape and are susceptible to decline later in life.

How You Can Protect Your Brain

You can help your brain function optimally and greatly reduce your risk for Alzheimer’s and dementia by eating healthy, moving your body, and keeping your weight under control. As indicated above, other lifestyle factors can also help protect your brain.


Moving your body is about the best thing you can do for your brain and to keep off the excess pounds. While the benefits of a workout have been well-known for below-the-neck for a long time, the many advantages for your brain have just recently been confirmed. Research is showing that physical exercise improves mood, memory, attention, creativity, and learning and reduces depression, age-related decline, and the risk of dementia and Alzheimer’s.


Healthy food benefits your heart, brain, and waistline. What you put into your mouth has everything to do with what goes on in your head today and as you age. The Mediterranean diet is currently the most highly recommended for overall health. The general guidelines for the diet are as follows:

  • Focus on fruit, vegetables, nuts, and grains.
  • Eat healthy fats, like olive oil.
  • Limit red meat.
  • Use herbs to flavor food rather than salt.
  • Eat fish and poultry at least twice a week.

Cognitive Activity

Complex and diverse mental challenges are a big component of brain fitness. While doing crossword puzzles and Sudoku are good, they aren’t enough because these activities ask you to recall things you already know. Your brain stays in top shape by doing new things and being challenged. You will want to push your brain beyond its comfort zone by learning new skills, hobbies, or sports, continuing to educate your mind, putting yourself in new social situations, and traveling to new locations. Even simple things like taking a new route to a familiar place, sleeping on the different side of the bed, or brushing your teeth with your nondominant hand can give your brain a mini workout.

Social Engagement

Many studies have shown that the more social a person is, the less likely they are to suffer a decline in cognitive skills and even motor skills as they age. Socializing is also associated with better health and fitness and a sharper, more agile mind at any age. Your brain is designed to interact with others and socializing activates and challenges many parts of your brain.

Specifically, the brain benefits of social engagement are:

  • Higher social engagement is associated with higher cognitive functioning and reduced risks of cognitive decline.
  • Volunteering helps lower mortality and depression rates and slows down the decline in physical health and cognitive function.
  • Larger social network sizes are associated with better cognitive function.
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  1. Sandra Pawula Reply

    Oh gosh, shocking news! Glad I lost 20 pounds this year. I hope I can get any lost function back!

  2. Allanah Hunt Reply

    What a fascinating article! Thanks for putting this so clearly 🙂

  3. Great information here, Debbie. I found this particularly interesting, “One study found that the brains of obese people looked 16 years older than their healthy counterparts while the brains of overweight people looked 8 years older.” Your article is reminding me to get out and go for my run this morning!

  4. Debbie this is brilliant, As i really watch what i eat , it amazes me that overweight people don’t see this and keep eating food that gives little nutrition. great info xx

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