Link Between Obesity and Brain Shrinkage?
A new study published in the medical journal Neurology is causing quite the commotion online, as the results point to a link between expanding waistlines and shirking brains.
As most of you know, BMI (body mass index) is one of the many metrics used by healthcare professionals and insurance companies to assess a person’s health and general fitness. BMI is determined by dividing an individuals’ weight in kilograms by the square of their height in meters.
Related - Is Obesity Really Dangerous?
Those with a BMI over 30 are generally considered obese and the further this number climbs the higher a person climbs up the scale of obesity rankings, which currently stands at I-V. And, in case you were wondering individuals with a Class 5 obesity rating have a BMI > 60 kg/m2.
Anyway, back to the study and the shrinking brains.
For the study, researchers analyzed the BMI, waist-to-hip ratio, and overall body fat percentage of 9,652 people with an average age of 55. Researchers also questioned test subjects in regards to their overall health.
Of the 9600+ individuals surveyed and measured, 19% were categorized as obese according to the metrics used by the researchers.
If you’re not familiar with waist-to-hip ratio, that metric is determined by determined by dividing waist circumference by hip circumference. It’s a unitless measurable, so it doesn’t really matter if you measure in Imperial units or Metric, FYI.
As you would expect, those with bigger bellies compared to their hips have higher waist-to-hip ratios. Men with a waist-to-hip ratio > 0.90 and women > 0.85 are considered to be centrally obese.
Body fatness was determined via Tanita BC418MA body composition analyzer using bioimpedance, which isn’t the most accurate method for determining body fat percentage for a whole host of reasons, none of which are really pertinent to this story since these people aren’t competing for world’s lowest or highest body fat percentage rating.
Subjects also underwent an MRI screening to determine their brain volume for white and gray matter as well as the volumes in the various regions of the brain.
What’s the difference between white and gray matter?
Gray matter contains the majority of brain's nerve cells. It also includes those brain regions involved in sensory perception, muscle control, and self-control, suggesting that less gray matter could, in theory, interfere with a person’s self-control, such as their ability to resist overeating.
White matter contains nerve fiber bundles that connect various regions of the brain to one another.
After adjusting for a host of other factors that potentially affect brain volume, such as level of physical activity, high blood pressure, smoking, and age, researchers noted that a high BMI was linked to slightly lower brain volumes. However, in those individuals with high BMI and high waist-to-hip ratios gray matter brain volumes were lower than those who just had a high BMI, but not a high waist-to-hip ratio. 
To put this into numbers:
- 1,291 people with a high BMI and a high waist-to-hip ratio had the lowest average gray matter brain volume of 786 cm3
- 514 people with a high BMI but without high waist-to-hip ratio who had an average gray matter brain volume of 793 cm3
- 3,025 people of healthy weight had an average gray matter brain volume of 798 cm3
Researchers noted that the present data suggest that the mixture of high BMI and waist-to-hip ratio is linked with an increase in gray matter atrophy. In other words, if you’re really, really fat (especially in the center of your body), your brain is shrinking, and it’s very likely your cognitive function is going downhill.
These findings are in line with some previous research suggesting a decline in certain types of brain cells with increasing levels of body fat.  This may indicate that being overfat and obese is a cause for increased risk of neurological degeneration.
What is less clear to the researchers is whether abnormalities in brain structure (caused by shrinkage of gray matter) lead to obesity or if obesity leads to the alterations in the brain.
One thing that needs to be mentioned is that of the people asked to participate in the study, only 5% participated. Researchers also remarked that those who volunteered for the study tended to be overall healthier than those who did not.
This means that the results might not accurately reflect the population as a whole.
What do you think?
Is obesity causing the brain to shrink? Or are people with smaller brain volumes more likely to become obese as a result of reduced self-control, appetite regulation, etc.
Or, do you think this study doesn’t tell us much of anything about the cause of obesity and that it’s nothing more than a bunch of weak associations?
Leave your comment down below.
1) Mark Hamer, G. David Batty. Association of body mass index and waist-to-hip ratio with brain structure. Neurology, Jan. 9, 2019; DOI: 10.1212/WNL.0000000000006879
2) Willette AA, Kapogiannis D. Does the brain shrink as the waist expands?. Ageing Res Rev. 2014;20:86-97.