Soy is a controversial yet one of the most nutritious, plant-based protein foods packed with all amino acids and health-promoting plant nutrients.
Recently, soy and its products have made a mark in the fitness industry. One can find soy everywhere–in smoothies, bars, salads and curries. People enjoy tofu, which is commonly known as ‘soy paneer’ in India. However, soy has a bad reputation among men as many think soy foods can drastically reduce testosterone levels, make their appearance feminine, lead to poor libido, and hinder muscle growth. But these beliefs are not supported by the latest scientific evidence.
Nutritional profile and health benefits
Before we critically review the existing evidence to draw any conclusion, let’s look at soy’s nutritional profile and health benefits. People living with cardiac complications, high cholesterol may benefit the most from soy products as revealed by decade-long research. Soy was also found to reduce the risk of some most common cancers. Mountain of sound scientific studies suggest soy and products have multiple health benefits:
*Soybean derived products are the only plant protein sources that contain all the essential amino acids. They are rich sources of fibre, vitamins, minerals and polyphenols, which is a type of antioxidant that prevents cell damage and protect cardiovascular health.
*A meta-analysis of 46 trials identified by the FDA found 25g per day soy protein reduced the ‘bad’ or LDL cholesterol by three to four per cent in adults.
*A systematic review involving more than 3,00,000 population reported 15 to 20 per cent reduced risk of stroke and heart diseases who consumed a soy-rich diet.
*Fermented soy products miso and nato were found to reduce mortality risk by 10 per cent in people who consumed those abundantly than people who did not.
Male fertility is not affected by soy
Soybeans are rich in a special class of polyphenol known as isoflavones or phytoestrogens as they are found to mimic the female hormone estrogen. Some experts suggest avoiding soy for men’s sexual health due to the presence of phytoestrogen. They believe soy isoflavone may reduce the level of testosterone thus lowering sexual function in men.
However, research suggests that soy isoflavones and estrogen have very different mechanisms of action and scanty evidence is available to connect disrupted male fertility with isoflavone intake, most of which are scientifically flawed too.
A 2008 small, pilot cross-sectional study found that men who were consuming very high amounts of soy foods had lower sperm concentration. The findings associated lower sperm concentration with higher ejaculation volume in men due to high consumption of soy foods. This doesn’t sound scientific. The same research group produced similar data in 2015 that failed to produce an association between soy food intake among men and fertility.
On the contrary, well-designed clinical interventions revealed no association between isoflavone intake and sperm concentration or quality. A study reported no effect on semen quality in healthy men who consumed a supplement containing 40 mg of isoflavones daily for two months. A 2010 clinical intervention resonated with this outcome.
Soy isn’t linked to male feminisation
Two case reports, one involving a 60 year old man and the other involving a 19-year-old type 1 diabetes male reported feminising effects, believed to occur due to soy food consumption. However, both these individuals were found to consume 360 mg/day isoflavones which are nine times more than the average intake among Japanese men.
In a 2010 review, the author reported neither isoflavone supplements nor isoflavone-rich soy foods affected total or free testosterone levels, sperm quality and oestrogen circulation. The study also argued that isoflavones don’t increase the risk of erectile dysfunction in men similar to findings reported in animal studies because the metabolism of isoflavone is different in rodents and human beings.
Another 2010 large meta-analysis published in Fertility and Sterility analysed 15 placebo-controlled studies with and 32 reports involving 36 treatment groups found neither soy foods nor isoflavone supplements had any effect on bioavailable testosterone concentrations in men of all ages.
Considering this evidence, the two case reports mentioned at the beginning of this section, therefore, suggest over-consumption-related abnormality that can be observed for any food, not only soy.
Soy foods lower the risk of prostate cancer
Prostate cancer is a huge concern among older males. This type of cancer is the second most prevalent cancer in men and the fourth most common cancer overall. Soy-based products were found to lower the risk of prostate cancer as revealed by multiple studies including Randomized Control Trials (RCTs) which are considered the ‘gold standard’.
The Adventist Health Study, 1998, involving 225 incident cases found frequent consumption of soy milk was associated with 70 per cent risk reduction of prostate cancer.
Recently, 2012 RCT fed 60 mg/day isoflavone for 12 days to 158 Japanese men and found the incidence of prostate cancer was 57 per cent lower in the isoflavone group compared to the placebo group that reported only 28 per cent risk reduction.
How much soy is safe to consume?
Common soybean-derived foods are edamame, tofu, tempeh, miso, soy flour, and soy milk. Evidence suggests excess, frequent consumption of soy products lead to some side effects in men. These studies used varieties of soy-soymilk, soy grits, tofu, isolated soy protein, isoflavone supplements. These studies stick to no more than 56 g of soy protein per day. The best way to know your individualised consumption is to work with a qualified dietitian.
That said, soy is not found to lower testosterone levels or sperm quality if not consumed in excess. Additionally, a myriad of evidence supports that soy-based foods may promote overall health, reduce mortality risk, lower cardiovascular disease risk, and prevent prostate cancer in men. If you still have any hesitation, visit a professional for more clarity and plan your diet better.
Next column: ‘Fruits are good but eating too much may damage your overall health’