Foods that lower oestrogen: true or not

On the internet it is easy to find advice like "eat broccoli to lower oestrogen" or "give up soy so you don't become effeminate". Among athletes such advice is often spread as a safe substitute for medication. The editorial team examined how food can actually affect the level and metabolism of oestrogens, which claims have grounding and which substantially exaggerate the real effects.

Oestrogen in men and women: why it is needed

Oestrogens are a group of hormones, the main of which is oestradiol. In women they are produced mainly by the ovaries, while in men oestradiol is formed mostly from testosterone in peripheral tissues under the action of the enzyme aromatase, in particular in adipose tissue, the brain and bones.

For men oestrogen is not an "enemy". It is needed for the closure of growth plates and the maintenance of bone density, normal lipid metabolism, libido and erectile function, and the work of the brain. Too low oestradiol in men is associated with loss of bone mass, worsened well-being and reduced libido.

Problems arise when the balance between androgens and oestrogens shifts. In men this happens with obesity, some liver diseases and endocrine disorders, as well as with the use of anabolic steroids, when an excess of testosterone is aromatised into oestradiol.

Thus the goal of "lowering oestrogen" is itself incorrect. It is correct to speak of a normal hormonal balance, which is determined by tests and the clinical picture, not by feelings or advice from forums.

Cruciferous vegetables and DIM

Broccoli, cabbage, Brussels sprouts and cauliflower contain glucosinolates, from which indole-3-carbinol is formed. In the stomach it is partly converted into diindolylmethane (DIM). Both compounds affect the liver enzymes that metabolise oestrogens.

As early as 1990, Michnovicz and Bradlow showed that taking indole-3-carbinol changed the pathways of oestradiol metabolism in humans — shifting it towards the formation of 2-hydroxyoestrone. However, it is important to understand: this is a change of metabolism, not a substantial decrease in the level of oestradiol in the blood.

The studies used concentrated supplements, not ordinary servings of vegetables. To obtain an analogous amount of indole-3-carbinol from food, one would have to eat very large volumes of cabbage every day. An ordinary serving of broccoli is good for health, but is not an "anti-oestrogen drug".

DIM supplements are widely advertised to athletes, yet there are no clinical studies showing that they prevent gynecomastia or lower oestradiol in men to a clinically significant level. Moreover, any active substance in high doses can have undesirable effects and interact with medications.

Soy, flax and phytoestrogens

Phytoestrogens are plant compounds that can weakly bind to oestrogen receptors. The best known of them are soy isoflavones and flax lignans. Because of this, soy is often considered a product that "raises oestrogen" in men, and flax a product that supposedly "blocks" it.

Clinical data do not confirm the fears about soy. The meta-analysis by Hamilton-Reeves and colleagues (2010) found no effect of soy protein or isoflavones on testosterone, free testosterone or SHBG in men, and the updated meta-analysis by Reed and colleagues (2021) also found no changes in oestradiol and oestrone at ordinary consumption.

Flax lignans are converted in the intestine into enterolactone and enterodiol, which have a very weak oestrogenic or anti-oestrogenic action depending on the context. The studies were mostly conducted in women in the context of breast cancer, and it is impossible to transfer them to male athletes.

As for mushrooms, Chen and colleagues (2006) showed that champignon extract suppresses aromatase activity in cell models and in animals. However, between a laboratory test tube and the real level of oestradiol in a human's blood there is a great distance, and there is no clinical confirmation.

Fibre, alcohol and body weight

Part of the oestrogens is excreted with bile into the intestine, where it can be reabsorbed into the blood. Intestinal bacteria affect this process, and fibre binds part of the hormones and promotes their excretion. In the prospective BioCycle study (Gaskins et al., 2009), a higher fibre content in women's diet was associated with a slightly lower oestradiol level.

Alcohol acts in the opposite way: systematic consumption is associated with a rise in oestrogen levels and a decrease in testosterone in men, partly through its effect on the liver. For a person who wants to support a hormonal balance, limiting alcohol has a much greater effect than any "anti-oestrogen" product.

The most important factor determining oestradiol in men is the amount of adipose tissue. It is in it that aromatase works actively, so obese men more often have lowered testosterone and a relative excess of oestrogens, and sometimes an enlargement of the breast glands (lipomastia or true gynecomastia).

Reducing excess body weight is the only dietary strategy with convincing evidence of an effect on the ratio of testosterone and oestrogens. No individual food can match the effect of losing 10–15% of body weight in an obese person.

What a diet cannot do

Among athletes who use anabolic steroids, the idea that an "anti-oestrogen diet" can prevent gynecomastia is widespread. This is a dangerous mistake. Supraphysiological doses of androgens create such an amount of substrate for aromatase that no food can cope with it.

The Endocrine Society review (Pope et al., 2014) describes gynecomastia as one of the common consequences of using anabolic steroids. Formed glandular tissue usually does not disappear on its own and in many cases requires surgical treatment. A diet will not help here.

• Tenderness, a lump under the nipple or an enlargement of the breast gland is a reason to see a doctor, not to change the diet.
• Taking on your own medications that affect oestrogens, without supervision, can lower oestradiol to a harmful level.
• Assessing hormonal balance requires tests: oestradiol, total testosterone, SHBG, LH, prolactin where indicated.

For women the question of "lowering oestrogen" has an entirely different context altogether: it is linked to gynecological and oncological conditions, where any interventions must be prescribed by a doctor. Dietary advice from the internet cannot replace specialised treatment here.

A realistic task of nutrition is to maintain a healthy body weight, provide a sufficient amount of fibre and limit alcohol. This creates conditions for a natural hormonal balance, but does not act as a medicine.

Editorial conclusions

No food lowers oestrogen enough for it to have clinical significance. Cruciferous vegetables and DIM change oestrogen metabolism, and the data on mushrooms and flax are mostly laboratory.

The fear of soy is not confirmed by clinical meta-analyses: at ordinary consumption it does not change hormone levels in men.

Real influence is exerted by body weight, alcohol and fibre. Gynecomastia associated with anabolic steroids or endocrine disorders is not treated by a diet — an examination by a doctor is needed.

The editorial team also recommends familiarising yourself with our materials about foods for raising testosterone, about oestradiol in men and about the gut microbiome and sport.

References

1. Hamilton-Reeves JM, Vazquez G, Duval SJ, et al. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil Steril. 2010;94(3):997–1007.
2. Reed KE, Camargo J, Hamilton-Reeves J, Kurzer M, Messina M. Neither soy nor isoflavone intake affects male reproductive hormones: an expanded and updated meta-analysis of clinical studies. Reprod Toxicol. 2021;100:60–67.
3. Michnovicz JJ, Bradlow HL. Induction of estradiol metabolism by dietary indole-3-carbinol in humans. J Natl Cancer Inst. 1990;82(11):947–949.
4. Chen S, Oh SR, Phung S, et al. Anti-aromatase activity of phytochemicals in white button mushrooms (Agaricus bisporus). Cancer Res. 2006;66(24):12026–12034.
5. Gaskins AJ, Mumford SL, Zhang C, et al. Effect of daily fiber intake on reproductive function: the BioCycle Study. Am J Clin Nutr. 2009;90(4):1061–1069.
6. Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.