Body fat is often thought as just a place where the body holds excess calories for later use.
But fat tissue is actually much more dynamic.
It behaves more like an organ, specifically an endocrine (hormone-producing) organ.
One of its most important roles is serving as a hormone reservoir. Fat tissue responds to hormonal signals and helps produce, convert, and store them, particularly estrogens.
This isn’t a new idea. It’s been documented for decades. In fact, some early researchers proposed naming estrogen “adipin,” a nod to its strong association with adipose (fat) tissue. The name “adipin” reflected its abundance in adipose tissue.
Estrogen is produced in fat cells, not just in ovarian cells. Fat cell production of estrogen ramps up as ovarian cell production of estrogen ramps down during menopause.
Once produced in the fat cells, it immediately binds to intracellular estrogen-binding proteins.
Because of this tight binding, most of the estrogen never makes it into the bloodstream, but instead acts locally within the tissue where it was produced.
The small amount that does escape into circulation is just a trace, which means blood tests don’t reflect the full estrogen burden. This is why some women can show “normal” or even “low” blood estrogen levels while still experiencing estrogen-dominant symptoms: because the tissue levels are high, not the serum levels.
There are two primary mechanisms behind estrogen storage and production in fat tissue:
- Aromatase: An enzyme within fat cells that converts androgens (like testosterone) into active estrogens.
- Stress-induced estrogen production: When tissues experience stress or injury, local estrogen synthesis increases.
This ability for every cell to produce estrogen is a remarkable survival strategy. Estrogen promotes cell proliferation and division. This is essential for repairing or regrowing tissues after an injury.
Relying solely on centralized estrogen production (like in the ovaries) would be inefficient and risky for rapid healing. Instead, the body allows localized estrogen synthesis wherever and whenever it’s needed.
Aromatase in fat tissue is so significant that when treating estrogen-driven cancers, it’s common to use drugs called aromatase inhibitors (exemestane, anastrozole, letrozole).
These inhibitors have been demonstrated to decrease estrogen levels by up to 98%.
If fat tissue weren’t such a major source of estrogen, why would these drugs work so effectively? This clearly shows how essential fat tissue is for estrogen production in the body.
Estrogen is stored primarily as estrone in fat, which is less potent than estradiol (the active form).
Storing estrogen in an inactive form prevents constant exposure to active estrogen, which could overstimulate tissues and disrupt normal cell function.
There are a lot of arguments that estrone is insignificant because it is less potent, however, estrone can be converted into estradiol and vice versa. This ability allows for the body to make the type of estrogen it needs on demand. The body is truly miraculous!
Stored estrone acts like a hormone reserve. Under the right conditions (like stress, inflammation, or enzyme activity), it can quickly become highly active and stimulatory.
People with higher body fat typically have higher estrogen levels. More fat tissue means more estrogen storage and aromatase activity, leading to increased estrogen production.
Aromatase activity also increases naturally with age, primarily because cortisol rises with age. High cortisol stimulates inflammation which stimulates aromatase.
So yes, ovarian estrogen production typically declines with age, like during menopause. However, this doesn’t necessarily mean your total estrogen levels are decreasing. Fat tissue stores and often produces enough estrogen to maintain or even raise overall estrogen levels.
So, what does this mean for hormone replacement therapy?
I’m not a fan of a one-size-fits-all approach, like automatically prescribing estrogen replacement the moment a woman experiences menopausal symptoms.
In my experience, many symptoms are due to low progesterone, not necessarily low estrogen. And starting with progesterone is a great strategy. As we age, body fat tends to increase, so a lot of women are still producing estrogen. Progesterone isn’t produced by fat tissue, so it’s common to become deficient, especially chronic stress.
Of course, some women genuinely need estrogen therapy. But therapy should always be personalized and given within the context of the patient. I have a lower BMI, so I apply estrogen as needed and I listen to my body everyday to adjust my hormone ritual.
And I always optimize my ritual with protective hormones (progesterone, pregnenolone, DHEA).
There are a lot of controversial opinions about hormones going around today. Regardless of new trends in hormone therapy or perspectives on social media, biology is objective. When we understand the mechanisms of each hormone, we can make better decisions about how to use them.
And like I always say, estrogen isn’t “bad.” But when it’s unopposed, especially stored or overproduced , it can drive symptoms and increase cancer risk. That’s why personalized care is so important. We have to look at the whole picture.