If you know you should lose weight, but haven’t quite summoned up the motivation to get the job done, today’s article may give you the extra push you need.

In a large observational study,1researchers measured body mass index (BMI) and waist-to-hip ratios found in men and women. Those with higher ratios of both had the lowest brain volume. The results were published in the 2019 issue of Neurology, the medical journal of the American Academy of Neurology.

The results don’t amount to absolute proof, but they’re powerful evidence. Here’s an explanation of what it all means. . .

BMI is a basic weight-to-height ratio that is determined by dividing a person’s weight by the square of their height. A BMI above 30.0 puts a person in the obese category.

The waist-to-hip ratio is determined by dividing waist circumference by hip circumference. Therefore, those people with bigger bellies compared to their hips have higher ratios. Men above 0.90 and women above 0.85 are considered centrally obese.

In layman’s terms, being pear-shaped may be bad for your brain. It’s already known that this body shape is connected to other medical problems.

Brain Loss

The study’s lead author Mark Hamer, PhD, of Loughborough University in England, explained the goal of the research.

“Existing research has linked brain shrinkage to memory decline and a higher risk of dementia, but research on whether extra body fat is protective or detrimental to brain size has been inconclusive,” he said.

“Our research looked at a large group of people and found obesity, especially around the middle, may be linked to brain shrinkage.

Researchers observed 9,652 people with an average age of 55. Of that group, about 1,000 participants with high BMI and waist-to-hip ratios had the lowest average amount of gray matter in the brain.

In contrast, the 3,000 participants with healthy weights showed an average amount of gray matter. Interestingly, about 500 participants with a high BMI — but not an excessively high waist-to-hip ratio — also had an average amount of gray matter.

You had to be in bad shape (literally) by both measures before brain loss was likely to be seen.

Good to be Gray

Gray matter contains most of your brain’s nerve cells. It’s found in regions involved with self-control, muscle control and sensory perception.

Scientists also believe there’s an association between general intelligence and the volume of gray matter in specific regions of the brain. Not surprisingly, those regions are the same ones implicated in memory, attention and language.2 White matter, somewhat less important for cognition, contains nerve fiber bundles that connect various regions of the brain.

Dr. Hamer explained that while the study found obesity, especially belly fat, was associated with lower volume of gray matter, the finding poses a chicken-or-egg question.

“It’s unclear if abnormalities in brain structure lead to obesity or if obesity leads to these changes in the brain,” Dr. Hamer said. “We also found links between obesity and shrinkage in specific regions of the brain.”3

He concluded that in the future measuring BMI and waist-to-hip ratio may help determine brain health. However, he also noted that further research is warranted.

I’ll just add that being overweight is closely correlated with high blood sugar and diabetes. The latter are known risk factors for dementia.

A Truly Random Group?

A shortcoming of the study was that only five percent of those invited to participate took part, and those who did tended to be in better health than those who did not. The results may not reflect the population as a whole.

When asked for his take-home message, Dr. Hamer said a healthy weight is important, but it’s just one piece of the brain health puzzle.

“We should encourage people to be physically active, not smoke, drink in moderation, eat a healthy diet, and keep blood pressure and cholesterol in check in order to keep the risk of dementia as low as possible,” Dr Hamer advised.

I agree. But even though we may not know what exactly links obesity, brain health and dementia risk, all indications say they’re entwined.


  1. Neurology Feb 2019, 92 (6) e594-e600; DOI:10.1212/WNL.0000000000006879
  2. http://www.memory-key.com/memory/gray-matter
  3. https://www.aan.com/PressRoom/Home/PressRelease/2688

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