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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