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Should Men Avoid Flax and Soya?


There are a number of male-oriented websites that often advise men to avoid flaxseeds and soya like the plague due to their feminising effects. Where does this advice come from and how correct is it? This article explores the mysteries of oestrogen in foods and male health.

What is oestrogen – and is it really in food?

Oestrogen is a hormone that is converted from androgens by specialised compounds called enzymes. Oestrogen is an important hormone in the sexual development of females, and starts to fall as they hit menopause.

Oestrogen, therefore, is often known as the female hormone, despite it naturally occurring in both genders.

Androgens make both the female hormone oestrogen and the male hormone testosterone in men and women alike – the difference is the amount it makes. These types of hormones are called steroids.

In women, the primary organ for making oestrogen is the ovaries and in men, the primary organ for making testosterone is the testicles.

Ovaries and testicles are collectively known as the gonads, because they are more well-known for producing sex cells such as ova (eggs) and sperm.

So that’s humans – plants are known to make a chemical that, structurally, looks very similar to oestrogen. It’s called phyto-oestrogen (phyto coming from Greek, meaning plant).

There are many theories of why phyto-oestrogen is made by plants, but it’s widely accepted that these chemicals are part of a plant’s defence mechanism – although also play a part in plant reproduction too.

There’s a school of thought that suggests that the phyto-oestrogens in red clover are responsible for grazing sheep to lose fertility – nature’s way of cutting down future generations of sheep from over-eating the flora!

It is also believed that in humans, phyto-oestrogen may be an endocrine disruptor. Endocrine disruptors (such as Bisphenol A)  in plastics have also been blamed in the past for the rising infertility in men.

In food, phyto-oestrogen as a disruptor fools our body into thinking it’s the same oestrogen that we humans make, and act in the same way. However, there really isn’t a wealth of research that studies phyto-oestrogen’s interruption on male health.

Foods containing phyto-oestrogens

There are three main forms of phyto-oestrogens: isoflavoneslignans and coumestans (mainly found in legumes). Isoflavones were discussed briefly in a previous article regarding gynaecomastia (or man-boobs).

The world’s largest source of isoflavones comes from soya (soy in the US) beans, and soya beans are processed to make products that are used in all aspects of the food industry including meats, meat-substitutes, bread, candy, and a wide variety of other foods.

According to a Guardian article published in 2006, up to 60% of all processed food will contain soya.

If you turn over any food product that has a long list of ingredients – you’ll often find soya or soy listed. Soya is often grown for animal feed and producing soya oil, which is used both as a biofuel and in food manufacturing.

There’s some evidence that phyto-oestrogens consumed by animals from animal feed can enter the human food chain of meat and dairy consumers.

However, the production techniques used to process soya will mean that isoflavone content will vary greatly.

The richest source of lignans is flaxseeds. Flaxseeds are often considered to be a good source of omega-3 oils, which are essential in our diet. Although flax only contains ALA, and so there is some doubt whether we get the same health benefits as we would from fish.

Phyto-oestrogens and Male Health

Phyto-oestrogens are absorbed by the body and therefore are measurable in the blood. However, they are considered to be a weak oestrogen, and do not have the same effect as the oestrogen we make ourselves.

But does this all matter? So what if we are consuming phyto-oestrogens, does it affect our health? The evidence, I’m afraid, is a mixed bag! It’s all going to boil down to what of the following health (or cosmetic) affect is most important to you!

The bottom line is, there just are not enough studies conducted looking at phyto-oestrogens and men’s health! So anyone suggesting that we should avoid them is basing it on weak scientific evidence or anecdotal evidence (e.g. a friend of a friend drank soya lattes for a year and grew boobs!).

Here are a few of the possible pros and cons of eating flax and soya:

1) Male-pattern baldness. Whilst the principal factor for baldness is genetic, there are some studies that have shown an association between drinking soya-based products and protection against baldness.

These findings are observational though, and thus only show association – not cause and effect.

2) Man-boobs (gynaecomastia). Some herbs have been suggested to be so oestrogenic that they can help women grow bigger breasts without surgery. The most common is fenugreek! If phyto-oestrogens can do this for women, can they for guys too?

Well it’s not known whether it really works in women to be honest, it’s not an area that is well-studied. Gynaecomastia is on the increase, and some statistics show that more men have it than don’t – in fact, as it’s such an embarrassing condition – many may go unreported.

At the same time, the amount of soya now being used in food manufacture has vastly increased, with the Americas now the biggest producers of it – but I would be surprised if there’s any real correlation.

3) Heart disease. You may have heard that green tea and red wine are good for the heart. This is based on components within them called polyphenols. In green tea, this is catechins and in red wine, resveratrol.

Both compounds are phyto-oestrogens, but act as anti-oxidants when consumed. In lab tests, these compounds have been found to be heart protective – but the research in humans is a little inconclusive.

4) Prostate cancer. A few studies conducted in the past have found an association between phyto-oestrogens and a reduced risk of prostate cancer in men. Particularly those found in soya. Later studies showed that lignans found in flaxseeds, grains and legumes had no significant effect.

Soya isn’t consumed as much in the western diet as it is in Asia, whereas with grains, the story is the other way around. Perhaps as we get older, there’s an argument to switch to more soya and less meat! But choose the least processed – since some plant nutrients are vulnerable to processing involving high heats.

5) Other cancers. Some studies have shown a lower risk of bowel cancer with soya consumption, although this is an association – not cause and effect.

6) Thyroid function. As previously mentioned, phyto-oestrogens in food are considered to be endocrine disruptors. It is this action that may create some problems with thyroid function. This might be welcome news for those with overactive thyroid glands, but not so good if the thyroid is underactive.

However, there really aren’t enough studies (or any large studies) to conclude that this is definitely the case. Some of the clinical trials that looked at this (in women) found that, whilst thyroid function was affected, blood pressure and insulin levels improved.

7) Obesity, diabetes and metabolic syndrome. There are a few studies (1,2,3) that have found a link between consuming phyto-oestrogens and lower weight, reduced risk of metabolic syndrome – which leads on to type 2 diabetes. Many of these studies have been conducted on post-menopausal women, so it’s not easy to conclude whether this is applicable to men also.

The studies conducted on men show some benefit, but largely, it’s an area not researched enough to make a conclusion one way or another. It’s possible that the link is due to dietary fibre rather than phyto-oestrogens!

8) Male infertility. There are both studies showing that there may be an association with soya intake and poor sperm function and others suggest that it’s too difficult to draw any conclusions just yet.

Soya consumption does not appear to affect outcome for IVF (in vitro fertilisation) however, although this is based only on one study.

Generally speaking, if a guy is trying for a family and he knows that he has a poor sperm count, then increasing the intake of fruits and vegetables is to be encouraged.

Getting protein from beans, legumes, pulses will always be controversial due to them containing compounds that can be harmful if not cooked properly or processed well.


Overall, eating more plants is a good thing – whether they contain high levels of plant-based oestrogens or not. Avoiding oestrogen in food is difficult, since it is prolific – but flax is certainly not a food to avoid, and very few of us could eat enough of it to get the levels of phyto-oestrogen that would have adverse biological effects.

Soya in the modern diet is usually found as a highly processed product, and therefore it’s probably unlikely that there are active phyto-oestrogens where these ingredients are found.

That said, it’s always good to keep highly processed foods to a minimum anyway.

So – should guys avoid flax and soya? Not really, there’s no conclusive benefit that it will either harm us or feminise us. In fact, both are more likely to be protective than anything.

Oestrogens in manufacturing (such as plastic) however, that might be a different story! But I’m a nutritionist, not an engineer – so that’s a question for someone else.

In food – if you’re not eating tofu for breakfast, lunch and dinner with flaxseed dressing – it’s highly unlikely you could eat enough for these compounds to affect you adversely.

Image Credit
Zsolt Joo –

So what do you think?

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