The propensity of women to deposit more fat in places such as the hips, buttocks, back of the arms, is a strategy against dementia and stroke.
Subcutaneous fat protects the female brain.
According to the scientists, women’s propensity to deposit more subcutaneous fat is protective against brain inflammation, which can cause problems such as dementia and stroke, at least until menopause. “We need to move beyond the simplistic idea that sex differences also lead to hormonal differences. We need to think more deeply about the mechanisms underlying these differentiations between men and women, so that we can address them and recognize the role that gender plays in different clinical outcomes,” says Alexis M. Stranahan, neuroscientist in the Department of Neuroscience and Medicine Regenerative from the Augusta University Medical College of Georgia. Diet and genetics _are other likely factors explaining the differences widely attributed to estrogen, says Stranahan, an author of a study published in the American Diabetes Association’s journal Diabetes.
The author acknowledges that the results are potentially groundbreaking and certainly surprising even to her. “We did these experiments to try to understand what happens first, the hormonal disruption, inflammation or brain changes.” To better understand how the brain becomes inflamed, they looked at increases in the amount and location of adipose tissue, as well as levels of sex hormones and then possible brain inflammation in male and female mice at different time points as they gained weight. with a high-fat diet.
Because, as in people, obese females tend to have more subcutaneous fat and less visceral fat than male mice, the researchers hypothesized that the different fat patterns could be a key reason for the inflammation protection females enjoy before death. menopause. They found no indicators of brain inflammation or insulin resistance, which increases inflammation and can lead to diabetes, until the female mice had reached menopause. At about 48 weeks, menstruation stops and fat placement in females begins to shift, becoming more similar to that of males.
They then compared the impact of the high-fat diet, which is known to increase body inflammation, in mice of both sexes following surgery, similar to liposuction, to remove subcutaneous fat. They didn’t do anything that directly interfered with normal estrogen levels, such as removing the ovaries. The loss of subcutaneous fat increased brain inflammationin females without changing the levels of estrogen and other sex hormones. Bottom line: Female brain inflammation looked much more like that of males, with increased levels of classic inflammation promoters, such as the signaling proteins IL-1β and TNF alpha in the brain, report Stranahan and his colleagues.
“When we took subcutaneous fat out of the equation, suddenly the females’ brains started exhibiting inflammation like the men’s, and females gained more visceral fat,” Stranahan says. The transition occurred over about three months, which translates to several years in human time.
Go beyond IBM
One lesson to be learned from this work: BMI, the Body Mass Index which simply divides weight by height and is commonly used to indicate overweight, obesity and consequently increased risk for a myriad of diseases, probably not a very meaningful tool. An easy and more accurate indicator of metabolic risk and potentially brain health is waist-to-hip ratio , which is also easy to calculate. “We cannot limit ourselves to talking about obesity. We need to start talking about where the fat is. That’s the critical element,” Stranahan says.
The author notes that the new study looked specifically at the hippocampus and hypothalamus of the brain. The hypothalamus controls metabolism and exhibits changes with inflammation due to obesity that help control the conditions that develop throughout the body as a result. The hippocampus, the center of learning and memory, is regulated by signals associated with these disorders, but it doesn’t control them, Stranahan notes. Also, since the accumulated evidence indicates that estrogen doesn’t explain the protection women enjoy, she Stranahan wants to better define what she does. One of her suspicions is the clear chromosomal difference between the XX female and the XY male.
The author notes that some believe that the reason females have higher subcutaneous fat stores is that they have sufficient energy stores for reproduction, and she does not question this relationship. But many questions remain, such as how much fat is needed to maintain fertility versus the level that affects metabolism, Stranahan says.
- Sex Differences in Adipose Tissue Distribution Determine Susceptibility to Neuroinflammation in Mice With Dietary Obesity (pubmed.ncbi.nlm.nih.gov)