Phytoestrogens: Benefits and Risks

Ryan Raman, MS, RD
Jul 15, 2017    Views: 188


Phytoestrogens are a highly debated topic in nutrition. That’s because this group of plant compounds can mimic or block the effects of estrogen.

Studies have found that phytoestrogens may offer several health benefits, including reducing the risk of heart disease and helping maintain healthy bones.

However, some people believe they can reduce fertility and disrupt your hormones.

This article looks at the benefits and risks of phytoestrogens to determine if they are healthy or harmful.


What Are Phytoestrogens?

Phytoestrogens are a group of naturally occurring compounds found in many plants. Foods that contain phytoestrogens include tofu, soybeans and flaxseeds.

The name comes from a combination of the Greek word for plant, which is “phyto,” and its similar structure to the sex hormone estrogen.

Estrogen is an essential hormone for female development and fertility. Men also have estrogen but at much lower levels.

Because phytoestrogens are structurally similar to estrogen, they can interact with its receptors in the body. Some phytoestrogens mimic the effects of estrogen, while others can block its effects (1).

These effects allow phytoestrogen to offer a variety of health benefits, especially for postmenopausal women. These may include reduced skin aging, stronger bones and a lower risk of heart disease.

There are four main families of phytoestrogens (2):

  • Isoflavones: The most studied type of phytoestrogen. Foods that contain isoflavones include soy and other legumes.
  • Lignans: A diverse class of phytoestrogens. Foods that contain lignans include flaxseeds, whole wheat, vegetables, strawberries and cranberries.
  • Coumestans: Although there are a variety of coumestans, only a few mimic estrogen’s effects. Foods that contain coumestans include alfalfa sprouts, clover sprouts and soybean sprouts.
  • Stilbenes: Resveratrol is one of the most common dietary stilbenes. Foods that contain resveratrol include nuts and red wine.

In addition, phytoestrogens belong to a larger group of plant compounds called polyphenols. Polyphenols have antioxidant effects and neutralize harmful free radicals (3, 4).

Summary: Phytoestrogens are a group of naturally occurring compounds found in many plant foods. They are structurally similar to estrogen, allowing them to mimic or block its effects.

Which Foods Contain Phytoestrogens?

Phytoestrogens are found in a variety of fruits, vegetables and other foods.

The following is a list of some foods that contain phytoestrogens (5):

  • Fruits: Apples, carrots, pomegranates, strawberries, cranberries, grapes
  • Vegetables: Yams, lentils, alfalfa sprouts, mung bean sprouts
  • Soy and soy products: Soybeans, tofu, tempeh, miso soup and paste
  • Nuts and seeds: Flaxseeds, sunflower seeds, sesame seeds, almonds, walnuts
  • Herbs: Red clover, licorice root, hops
  • Beverages: Coffee, bourbon, beer, red wine
  • Grains: Oats, barley, wheat germ
  • Oils: Olive oil, jasmine oil

Interestingly, the number of phytoestrogens in plant foods can depend on several factors, including where the plants were grown, when they were harvested and weather conditions (6).

Summary: Phytoestrogens are found in a variety of plant and vegetables. The phytoestrogen content of foods can depend on a variety of factors.

How Phytoestrogens Affect the Body

Estrogen works by binding to its receptors in cells (7).

When this happens, estrogen and its receptor travel to the cell nucleus, or command center, to change the expression of several genes.

However, cell receptors for estrogen are not very selective. In some cases, substances with a similar structure can bind to and activate them.

Thus, given that phytoestrogens have a similar chemical structure to estrogen, they can also activate its receptors (8).

For this reason, phytoestrogens are known as endocrine disruptors. These are chemicals that interfere with the normal function of hormones in the body.

However, phytoestrogens can only bind weakly to estrogen receptors, producing a much weaker response than normal estrogen (9).

Summary: Phytoestrogens are structurally similar to estrogen. This allows them to activate estrogen receptors in the body. However, the effects of phytoestrogen are much weaker than estrogen.

Health Benefits of Phytoestrogens

Diets rich in phytoestrogens have been linked to some impressive health benefits.

Here are a few ways that phytoestrogens may improve your health.

May Reduce Risk Factors for Heart Disease

Heart disease is the leading cause of death worldwide (10).

People with higher blood levels of cholesterol, triglycerides, “bad” LDL cholesterol or high blood pressure have a higher risk of heart disease than others (11).

Many studies have shown that consuming foods rich in phytoestrogens may reduce these risk factors for heart disease (12, 13, 14, 15, 16).

For example, an analysis of 38 studies found that consuming 31–47 grams of soyprotein daily reduced blood cholesterol by 9%, triglycerides by 10% and LDL cholesterol by 13%, on average.

Additionally, people in the study with the highest cholesterol levels (greater than 335 mg/dl) had reduced their cholesterol levels by 19.6% (16).

Interestingly, the US Food and Drug Administration (FDA) approves health claims regarding soy protein and the prevention of heart disease (17).

May Support Bone Health

Building healthy bones is incredibly important, especially as you age.

A diet rich in phytoestrogens may prevent osteoporosis, a condition that is associated with bone loss and porous bones (6).

Animal studies have shown that phytoestrogens can decrease the formation of osteoclasts, a type of cell that breaks down bones. In addition, they can increase the formation of osteoblasts, a type of cell that helps build bones (18).

Furthermore, human studies have found that people with a diet rich in phytoestrogens have a lower risk of hip fractures (19).

However, studies on phytoestrogen supplements show conflicting results.

An analysis including 10 studies found that taking an isoflavone supplement for at least one year did not significantly increase bone density of the hip or spine (20).

However, a more recent analysis including 14 studies found that taking an isoflavone supplement increased bone density by 54%, compared to a placebo. These studies lasted from one month to two years (21).

The link between phytoestrogens and bone health seems promising. Nevertheless, future studies in this area would help clarify this connection.

May Reduce the Effects of Skin Aging After Menopause

Menopause is the stage in a woman’s life when she stops menstruating.

It results in a decline in estrogen levels, which can lead to skin wrinkles, thinning and dryness (22, 23, 24).

Studies have found that applying phytoestrogens to the skin could reduce the effects of skin aging after menopause (24, 25).

In a study in 30 postmenopausal women, scientists found that applying a phytoestrogen extract to the skin helped increase thickness by nearly 10%.

In addition, collagen and elastic fibers increased in 86% and 76% of women, respectively (25).

May Reduce Chronic Inflammation

Inflammation is a process that helps the body fight infections and heal wounds.

In some situations, inflammation can persist for a long time at low levels. This is called chronic inflammation, and it is linked to many harmful diseases.

Fortunately, phytoestrogens like isoflavones may have anti-inflammatory effects on the body.

Animal studies have shown that phytoestrogens like isoflavones decrease several markers of inflammation, including IL-6, IL-1β, nitric oxide and prostaglandin E2 (26).

Likewise, human studies have found that consuming a diet rich in isoflavones may reduce markers of inflammation such as IL-8 and C-reactive protein (27, 28).

May Reduce the Risk of Certain Cancers

Cancer is a disease characterized by uncontrollable cell growth.

Diets rich in phytoestrogens have been linked to lower risks of several cancers, including prostate, colon, gut, endometrial and ovarian cancer (29, 30, 31, 32, 33, 34).

For example, an analysis of 17 studies found that consuming soy isoflavones was linked to a 23% lower risk of colorectal cancer (33).

However, the evidence between phytoestrogen intake and breast cancer is conflicting (35, 36).

On one hand, studies show that people who consume the most isoflavones have a lower risk of breast cancer (37, 38, 39).

On the other hand, animal studies show that phytoestrogens like soy isoflavones can increase the risk of breast cancer (40, 41, 42).

Future studies will help determine how phytoestrogens affect the risk of breast cancer.

Summary: Diets rich in phytoestrogens have been linked to a variety of different health benefits, especially in women.

Health Risks of Phytoestrogens

Most studies suggest that phytoestrogens may benefit your health.

However, there is some concern that a high intake of phytoestrogens can disturb your body’s hormone balance.

Here are a few risks associated with high a phytoestrogen intake.

May Reduce Fertility in Male Animals

Given the ability of some phytoestrogens to mimic the effects of estrogen, some question whether they are harmful for men.

While men have some estrogen, significantly elevated levels of it are not normal.

Increased levels of estrogen in relation to testosterone may reduce male fertility (43).

For example, animal studies on cattle, sheep and cheetahs have shown that regular phytoestrogen consumption is linked to lower fertility among males (44, 45, 46).

However, there is no strong evidence to show that a high intake of phytoestrogens among men can reduce their fertility (47, 48, 49).

For example, in an analysis of 15 studies, scientists found that neither soy isoflavones in food nor supplements reduced testosterone levels in men (49).

May Affect Thyroid Function for Some

The thyroid gland helps regulate your metabolism, growth and development (50).

Unfortunately, some phytoestrogens like isoflavones can behave as goitrogens, which are compounds that can interfere with the function of the thyroid gland (51).

A few studies in animals and humans have found that consuming phytoestrogens may affect the function of the thyroid gland (52, 53, 54).

However, most studies on healthy adults have not found a strong connection between phytoestrogens and thyroid function (55).

For example, an analysis of 14 studies found that consuming soy foods, which are a great source of isoflavones, had no strong effects on healthy adults.

Nevertheless, they found that soy foods might affect thyroid function in people with hypothyroidism or an iodine deficiency (55).

In short, consuming phytoestrogens likely won’t affect your thyroid function unless you have pre-existing thyroid issues or an iodine deficiency (56).

Summary: Diets rich in phytoestrogens likely won’t affect healthy adults. However, there may be some concern for people with pre-existing thyroid problems or an iodine deficiency.

How to Add Phytoestrogens to Your Diet

If you would like to benefit from phytoestrogens, eating whole foods is the way to go.

They provide you with a healthy dose of phytoestrogens and a variety of other nutrients important for optimal health.

The following are a few ways you can add phytoestrogens to your diet:

  • Add 1–2 tablespoons of flaxseeds to your smoothies
  • Have a soy-based meal two to three times per week
  • Eat a few pieces of fruit, such as strawberries, cranberries and grapes, daily

The safety of phytoestrogen supplements is still unclear.

While some studies have found supplements harmless, others suggest avoiding them until the long-term risks are known (57, 58).

Summary: Many whole foods are rich in phytoestrogens, including flaxseeds and certain fruits. More research is needed regarding supplements.

The Bottom Line

Consuming a diet rich in phytoestrogens is linked to a variety of health benefits, especially in postmenopausal women.

In addition, there is no strong evidence that shows it can reduce fertility in healthy males. Moreover, it likely won’t affect thyroid function in healthy adults.

If you would like to reap the benefits of phytoestrogens, try adding a variety of phytoestrogen-rich foods into your diet.

Foods like soybeans, flaxseeds and sesame seeds are excellent sources.

From our friends at Authority Nutrition