What is menopause doing to our metabolism?

Wendy Kohrt, PhD, has spent 30 years studying what any woman who has hit 50 already knows: changing hormones impact almost every facet of our metabolism.

The University of Colorado exercise physiologist and geriatric medicine division professor has conducted hundreds of studies on diminishing ovarian function in animals and humans over the decades.

Her work, which she presented to the 2020 North American Menopause Society Virtual Annual Meeting, involves suppressing ovarian function in animals and pre-menopausal women to mimic menopause-related hormonal drops.

What her research shows is that how we gain and carry weight is often all about the estrogen we do or don’t have. Keep reading to learn what her research revealed.

How does a drop in estrogen lead to weight gain?

"When we suppress ovarian hormones, the resting metabolic rate goes down. It goes down by the equivalent of about 50 to 70 calories a day. That doesn't seem like a lot. That's half a piece of bread.

If that goes on over time—without you reducing how much you're eating or increasing how much you’re exercising—you’d see an increase in fat mass of one pound over about two to three months. It really is a fairly substantial disruption in energy balance.

Women who received estrogen rather than the placebo didn't have that shift, that propensity for weight gain due to a decrease in resting metabolic rate."

What about how we carry our weight?

"The fat tends to come on in the belly region and not right under the skin. It tends to accumulate behind the muscle wall around the vital organs. We call that visceral fat or intra-abdominal fat. The fat in that region has been associated with risk for certain chronic diseases, like heart disease and type 2 diabetes and hypertension."

What happens to fat distribution in women who take hormone therapy?

"We found that the women who received estrogen did not have that increase in belly fat that the placebo treated group did. We think estradiol [estrogen] is also important in regulating where fat goes to be stored in the body. We're trying to understand that, but I think the key point is that going through menopause is a life transition that could increase risk for these chronic diseases associated with abdominal obesity."

And what about the impact of estrogen on our muscle mass?

"We know that bone loss occurs when estradiol levels or estrogen levels decrease in women. What we see is that over five to six months of suppressed ovarian function, women lose about a kilogram—about two to two and a half pounds—of lean mass.

We also did CT scans and also scans of the mid-thigh, and what we saw is that muscle size was shrinking in response to a suppressing ovarian function. That, too, was prevented in the women who got estrogen patches to wear."

What role does exercise play?

"We've got some signals from our very preliminary data that being active does help, but it doesn't take the place of estrogen."

How does reduced estrogen impact our energy levels?

"What several studies have demonstrated is that when ovaries are removed from female animals—mice, or rats, a few other species—their spontaneous physical activity decreases within a week of that surgery. Not by 5, 10, or 15 percent, but more like 50, 60, or 70 percent.

Animals that get estrogen added back go right back into their running wheels, just as active as they were before they had their ovaries removed.

This is another piece of evidence that estrogen regulates our energy balance."

What's your opinion on when to take hormone therapy?

"The unique thing about the WHI, Women's Health Initiative, trials is that the average age of women in that trial was, I think, mid-to-late 60s. They were many years removed from menopause. I think what has evolved from those trials and other subsequent studies is that the risks of estrogen use may be very different at the time of menopause than if you wait several years and then start estrogen therapy.

Studies in monkeys who had their ovaries removed and were put on a high-fat, high-cholesterol diet developed atherosclerosis (the buildup of fat in their artery walls) as a result of that dietary intervention if they didn’t also receive estrogen. The animals that were given estrogen at the time they were ovariectomized, their arteries stayed clean.

Estrogen had a protective effect against the development of atherosclerosis.

In another group of monkeys, it was the human equivalent of about five to seven years later when they started their estrogen. The estrogen wasn't effective at preventing further atherosclerosis; it seemed to have a neutral effect.

Then there was still another group of animals that got started on estrogen the equivalent of about 10 human years later. When that group got estrogen, it was actually harmful.

That might be similar to what was observed in the Women's Health Initiative trials. In older women who started estrogen relatively late in life, there was a small increase in risk for cardiovascular disease, and stroke."

So you would advise estrogen early rather than later?

"We don't have the level of evidence I would like to see, but I think when I look at the broad spectrum of research that's been done in humans, in animals, and even in cells at a very small level, there's a consistency that estrogen has favorable effects if it is never allowed to decrease. If it decreases and stays low for many years, it might not be safe to bring estrogen levels back up."