Whether we like it or not, everyone accumulates fat.
In women, this usually accumulates around the hips, resulting in a pear-shaped appearance. In men, fat tends to build up around the abdomen, resulting in an apple shape.
As it turns out, being a pear is healthier than an apple.
A research team from the University of California at Riverside has found that only male mice experience neuroinflammation or activation of the immune response in the brain after a high-fat diet. While the females were unaffected, the males showed low testosterone levels and a reduced sperm count in addition to neuroinflammation.
Study results appear in the journal Limits in Immunology,
Clinical studies have led researchers to believe that women are protected against weight gain when young, due to ovarian estrogen. The understanding was that postmenopausal women gain weight due to a steep decrease in estrogen, leading to a decline in health parameters including obesity.
"We have addressed this assumption by removing ovaries in young mice," said Djurdjica Coss, Associate Professor of Biomedicine at the UCR School of Medicine, who led the study. "We found that the mice increase when fed on a high-fat diet, which suggests that ovarian hormones actually protect against weight gain, but we also found that these female mice show neither neuroinflammation nor reproductive hormone changes other factors than ovarian estrogen are protected. "This is a new finding."
The results derived from the mouse study are likely to have applications in humans, Coss added.
"High fat diet mice develop metabolic syndrome – a constellation of pathologies that includes type 2 diabetes and insulin resistance – much like overweight people," she said. "Overweight men have lower testosterone levels and contribute to lower libido, lower energy, and decreased muscle strength, as we see in mice, overweight male mice showed nearly 50 percent decrease in testosterone and sperm count, and overweight women have difficulty with their menstruation Ovulation and overweight female mice show the same, leading to reduced fertility. Interestingly, 18 percent of couples in the United States now need medical intervention – hormone treatments, in vitro fertilization – to produce a child is a likely factor. "
Increasing obesity is a public health problem in the United States, where more than 30 percent of people are overweight and more than two thirds are overweight. Obesity is associated with mental deterioration and an increased rate of stroke, in addition to other problems affecting the internal organs. In the US, some ethnic minorities are disproportionately affected by obesity.
Female women and mice deposit fat differently than their male counterparts. Women deposit fat subcutaneously, just under the skin, while men accumulate fat deeper into the visceral region of the body, which can affect internal organs.
Finally, the subcutaneous regions are flooded with fat even in women, and the abdominal region shows obesity, leading to neuroinflammation.
"While overweight, women are better protected than men, where neuroinflammation is affected," said Coss. "This could be evolutionary protection for women who have to undergo more weight changes as a result of pregnancy, and this protection is severely limited if obese women become obese and fat accumulates around the waist."
Next, Coss and her team will study in mice how the abdominal weight is related to neuroinflammation.
"We know that belly fat – that is, fat around the internal organs – is inflamed with a fat overhang," she said. "This fat then recruits immune cells from the bloodstream that are activated."
Another important finding in the study is that peripheral immune cells, especially macrophages, cross the blood-brain barrier – the protective barrier that stops the influx of most compounds from the blood into the brain. This infiltration of peripheral immune cells into the brain occurs in addition to the activation of resident immune cells.
"The brain was considered an 'immune-protected site,' but we show that peripheral inflammation" spills "into the brain, which in turn can cause the neuronal problems mentioned above," Coss said.
Coss stated that it is unclear what causes this activation and that her research team is planning further investigations.
"We know that the immune cells secrete cytokines that are inflammatory markers in the blood, and it's possible these cytokines in blood migrate out of adipose tissue and activate immune cells to cross the blood-brain barrier," she said. "It's also possible that other immune cells contribute to neuroinflammation and obviously our work has produced several research questions that we would like to answer."
Coss recognized weight is also a sensitive issue for clinicians who have a hard time talking about patients.
"After all, we connect food with happiness, social interactions, and family reunions," she said. "Still, my advice is:" Take care of your diet! And pay attention to body weight, especially around the stomach. "