What Causes Menopausal Belly Fat?
Most women have a love-hate relationship with estrogen. Studies have shown high levels are at least partially to blame for premenstrual syndrome, endometriosis, fibroids and even breast cancer. But when menopause hits and estrogen levels drop to an all-time low, women suffer from hot flashes, mood swings and bone loss. To top it off, as estrogen levels decline, women gain belly fat.
A new study published in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism shows that postmenopausal women who undergo hormone therapy to relieve menopausal symptoms tend to have less fat tissue, especially in the belly, compared to other postmenopausal women.
For the study, researchers collected data on hormone therapy use in 1,086 postmenopausal women between ages 50 and 80. All the women included in the study underwent dual-energy X-ray absorptiometry scans to measure their body fat. The researchers found that the women who were currently on menopausal hormone therapy, which involves ingestion of estrogen alone, estrogen and progesterone or estrogen and progestin, a synthetic hormone that's similar to progesterone, had significantly lower levels of belly fat than the women who had never received menopausal hormone therapy.
What's more, researchers found that when women stopped hormone therapy, they quickly started to gain belly fat, says Dr. Georgios E. Papadakis, chief resident in endocrinology, diabetes and metabolism at Lausanne University Hospital in Lausanne, Switzerland, and the study's lead author.
The study adds to the growing evidence that the loss of estrogen is a main driver of menopausal fat gain. A previous 2014 review published in the journal BioMed Research International notes that obesity becomes significantly greater in American women after they reach age 40, around the onset of perimenopause, the gradual transition period to menopause. According to the review, 65 percent of women ages 40 to 59 years are obese, and 73.8 percent of women 60 years and older are obese. Researchers note that, during this process, women store the majority of their weight gain as abdominal fat, also called visceral adipose tissue.
"It's not the kind [of fat] you can pinch under your skin. It's actually behind the abdominal wall and around some of your vital organs," explains Wendy M. Kohrt, professor of medicine in the division of geriatric medicine at the University of Colorado Anshutz Medical Campus and Nancy Anshhutz Endowed Chair in Women's Health Research. Her current research suggests that a complete loss of estrogen causes visceral fat to increase by 10 percent in just five months.
"The concern is that fat that gets stored in that region is associated with an increased risk for Type 2 diabetes, heart disease and other chronic health issues," Kohrt says. In a 2017 animal study published in the journal Oncogene, Michigan State University researchers found that visceral fat tissue produces large amounts of fibroblast growth factor 2, a protein that can cause a healthy cell to turn cancerous.
So how does a loss of estrogen drive menopausal abdominal fat gain? Researchers are still working to pinpoint the exact mechanisms, but studies have already identified four ways decreasing levels of estrogen can trigger an uptick in belly fat. Here are some culprits – and how to avoid them – according to experts.
1. A slowing metabolic rate. It's no surprise that, as you age, your metabolism declines. However, in one 2015 study published in the Journal of Applied Physiology, Kohrt and her team found that estrogen contributes to that drop. "When we suppressed ovarian function in premenopausal women, resting metabolic rate went down," she says, noting that when they replaced estrogen but no other ovary-produced hormones, the participants' resting metabolic rate went back up. "Without estrogen, resting metabolic rate goes down by about 50 calories per day, which doesn't seem like much, but it's actually a pretty big disruption in energy balance."
Over the course of three months, that metabolic drop could add up to a pound of weight gained. So, without reducing their caloric input through a diet or increasing their caloric expenditure through physical activity, over the years postmenopausal women can naturally gain dozens of pounds through a lowered metabolic rate alone.
2. A changing fat cell type. Why do pounds gained tend to accumulate around the middle? It may have to do with a newly discovered type of fat cell. Unlike traditional fat, it comes from bone marrow stem cells and is more prone to accumulate in the abdomen and around the heart.
Two 2015 studies published in Cell Metabolism and The FASEB Journal demonstrate how these bone marrow stem cell-derived fat cells are more prevalent in women than in men, and how they increase with age. That suggests that estrogen may play a role in their proliferation, according to researchers. The newly discovered fat cell is also more likely to produce cytokines, inflammation causing substances that inhibit insulin sensitivity, thereby increasing the risk for Type 2 diabetes.
3. Disrupted sleep patterns. Declining estrogen levels may also trigger abdominal weight gain through a less direct mechanism, including by disrupting sleep. "Dropping estrogen levels in the perimenopausal period causes the trifecta of the acute menopausal transition: moodiness, hot flushes and insomnia," says Dr. Heather Macdonald, an OB-GYN with Hoag Memorial Hospital Presbyterian in Newport Beach, California. All three can contribute to poor sleep and, thus, visceral fat, she says.
For example, 2008 research published in the International Journal of Obesity links sleeping less than five hours per night to abdominal fat gain. Subsequent research has identified that poor sleep can increase levels of the stress hormone cortisol, which increases the tendency to store fat around the waist, Macdonald says. She adds that poor sleep can also increase appetite, cravings for high-calorie and high-fat foods and the tendency to overeat.
4. Reduced activity levels. Mice love their running wheels. "But if you take their ovaries out, within a week after surgery, their spontaneous physical activity levels just plummet," Kohrt says. "And they don't go down by 5, 10 and 15 percent. They go down by 50, 60 and 70 percent. They become very sedentary, and if you give them back estrogen, they're right back in their running wheels."
"Our evidence of this in humans is preliminary so far but we've got some evidence," Kohrt says. In fact, we've got a paper that's in press now and will be coming out soon to show that physical activity levels decline in ovary-suppressed women," she says. "The decline is much subtler than in animals, but there's still a hint that when estrogen levels are low, there's a biological drive toward becoming more sedentary."
Obviously, moving less throughout the day can increase the risk of weight gain, but Macdonald notes that a decline in exercise also exacerbates sarcopenia, the age-related loss of muscle mass. Muscle mass is a primary determining (and modifiable) factor in determining metabolic rate, she says, and muscle loss is consistently linked with metabolic declines and abdominal fat gain.
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