**EP311: Fat Bellies and Skinny Brains**
**Dr. Auric Bishop:** Welcome, my name's Dr. Auric Bishop. I'm a cardiologist, an author, and a keynote speaker. I'm CEO of the Healthy Heart Network. I'm all about trying to help people live as well as possible for as long as possible. Heart disease is huge in Australia. Every 20 minutes, someone suffers a heart attack. Most of these could probably have been avoided if only we knew what to do. This podcast is all about helping you understand blood pressure, weight, and cholesterol for better health. If you enjoy this podcast, I would be honoured for a five-star review. You can share it with your family and friends. It may well save someone you love.
**Warwick Bishop:** Hi, my name is Warwick Bishop, and welcome to my podcast and videocast station. I'd certainly like to thank you for tuning in and taking a moment to have a listen. I hope that today, when I share a little bit about abdominal fat and the size of your brain, you find it informative and interesting.
Well, I'm going to share with you an article that came through on Medscape that I subscribe to. It was written by Megan Brooks in September of 2023. I'll be reading bits of it because it's a really nice and interesting summary. The article is called "Abdominal Fat Linked to Lower Brain Volume in Midlife."
New research provides strong evidence of an association between abdominal fat and reduced brain volumes, particularly with those involved with cognitive function. In a large study of healthy middle-aged adults, greater visceral and subcutaneous abdominal fat—so visceral means fat around the organs, and subcutaneous fat means fat under the skin—demonstrated on abdominal MRI, or magnetic resonance imaging (that's the scanning we do that doesn't use contrast, it uses water particles), predicted brain atrophy on imaging. This was especially so in women.
In quotes, the study shows that excess fat is bad for the brain and worse in women, including in Alzheimer's disease risk regions. This was said by lead author Cyrus Raja, who is MD, PhD with the Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri. Well, the study was published online in August in the journal *Aging and Disease*.
Multiple studies have suggested a connection between body fat accumulation and increased dementia risk, but few studies have examined the relationship between the types of fat—that is, visceral (the fat that hangs around the organs, which we generally think of as a worse indicator of cardiovascular risk) versus subcutaneous fat (i.e., the fat that hangs just under the skin, that we might see in a chubby child). The examination of the relationship between those types of fat and brain volume just hasn't been done.
This most recent study, however, looked at 10,000 healthy adults between 20 and 80 years of age, with a mean age of nearly 53 years, and 53% being men. They underwent a short whole-body MRI protocol. They did analysis on the abdominal fat types, and normalized brain volumes were evaluated. They were controlling for age and sex. The research team found that higher amounts of both visceral and subcutaneous abdominal fat predicted lower total grey and white matter volume.
Well, you may remember grey matter is the neurons, the actual cells that form the brain and do, if you like, most of the work, and that the white matter are the axons travelling together, like the wiring between the cells, the functional component. But both appear to be affected, as well as a lower volume in the hippocampus, the frontal cortex, and temporal, parietal, and occipital lobes. So almost the entire brain and its functional capacity could be affected by these higher levels of visceral and subcutaneous fat.
In quotes, "The findings are quite dramatic," Raji comments, "Overall, we found that both subcutaneous and visceral fat had similar levels of negative relationship with brain volumes." Women had a higher burden of brain atrophy with increased visceral fat than men. However, it's difficult to place the sex differences in context due to the lack of prior work specifically investigating visceral fat, brain volume, and sex differences, so it's very hard to compare and know for sure what this means. This is a note of caution from the researchers.
But they also note that whilst statistically significant relationships were observed between visceral fat levels and grey matter volume changes, their effect sizes were generally small. So someone could be carrying a fair bit of extra weight, but that may not have a huge impact on that person as an individual. Where the significance of this study really bore out was when they took lots of people who were carrying extra weight; they found that there was, across the board, a reduction in brain volumes.
But there are limitations. Other limitations include the cross-sectional nature of the study, which really precludes conclusions about causality. They didn't really assess whether increasing visceral or subcutaneous fat then had a subsequent effect on brain volume. They just took a bunch of people. The analysis also didn't account for other lifestyle factors such as physical activity, diet, genetic variabilities, and perhaps even issues with blood pressure overnight. So there's a number of things that could have played into this, but still an interesting starting point.
The researchers do call for further investigation so they can better elucidate underlying mechanisms and discover possible interventions, particularly trying to understand more around abdominal fat, its interaction with the brain, and the impact of reducing fat. Commenting on this research, Claire Sexton, who's an Alzheimer's Association Senior Director, says that previous studies have linked obesity with cognitive decline and increased risk of dementia. Rather than using BMI as a proxy for body fat, this particular study used a measured volume of visceral and subcutaneous fat by MRI imaging, which is a different approach.
Sexton was not associated with the study, but said that the finding that increased body fat was associated with reduced brain volume suggests a possible mechanism to explain the previously reported associations between obesity and cognition. To say that though some degree of atrophy and brain shrinkage is common with old age, awareness of this association is important because reduced brain volumes may be associated with problems with thinking, memory, and performing everyday tasks. Because rates of obesity are continuing to rise in the Western world, along with obesity, such conditions as heart disease, stroke, type 2 diabetes, together with cancer, are also increasing.
So, overall, considered an interesting addition to the literature of the study, it didn't necessarily take into account some of these confounders like physical activity and diet, which could have an important relationship. It's really quite important to recognize that overall it's probably not just one factor. So although this study was able to show some associations between visceral and subcutaneous fat, it's really very important to look beyond that to other factors, which include diet, physical exercise, etc., when considering the association between cognitive decline and/or dementia.
So, although obesity and the location of fat seem to be important in considering one's likelihood for development of brain shrinkage, i.e., dementia, such things as education level, physical activity, previous head injury, poor sleep, mental health, and so on and so forth, all play in as well. Interestingly, the Alzheimer's Association is leading a two-year clinical trial known as US Pointer to see whether combining physical activity, healthy nutrition, social and intellectual challenges, and improved self-management of medical conditions can enhance cognitive function in older adults who are at increased risk for cognitive decline.
We'll need to watch this space to figure out where that leads us. But in the meantime, I think we really do get a good sense that carrying too much weight—whether it is visceral weight, i.e., that nasty fat that hangs around the organs deep inside your body and is often closely linked with the risk of development of diabetes and coronary disease, or even the other sort of fat, subcutaneous fat, which is more a chubby child sort of fat—both of these are problematic.
I think it reminds us that if we're going to look after our health and if we're going to look after our brain health, we probably want to be minimizing weight gain. We want to be maximizing exercise and good nutrition, and we want to be keeping active, not just physically, but cognitively as well. Watch this space for more on weight, whether it's visceral or subcutaneous. But let's group it under obesity and its association with dementia.
For now, look after yourself. If you've got any queries or questions, drop us a note. I hope you found this "Chubby Belly, Skinny Brain" podcast interesting and informative. I hope it motivates you to look after your health. Wishing you the very best. I hope you live as well as possible for as long as possible. Take care and bye for now.
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