Evidence: High Possible Benefits: High Safety: Very High
TABLE OF CONTENTS
What are soy isoflavones?
Soy isoflavones are bioflavonoids found in soy. They are commonly used as a dietary supplement for their wide variety of benefits. This article is about the main benefits of soy isoflavones, their potential side effects, the best time to take them, and more.
Possible benefits
All of the potential benefits mentioned below are dose-dependent. As with most other supplements, there is a sweet-spot dose that allows you to get most of the benefits without causing meaningful side effects or tolerance buildup in the body. We will discuss the best dosing protocol later in this article.
Major benefits
Reduced risk of cancer – Soy isoflavones can greatly reduce the risk of breast cancer and possibly other types of cancer.
Minor benefits
Improved skin health – Many animal studies show promise in soy isoflavone supplementation for improving skin health. The supplement was shown to improve skin elasticity, healthy skin structure, fibroblast renewal, and dermal vascularity. It also helps the skin adapt to environmental stress.
Antioxidant properties – The supplement has potent antioxidant properties and can reduce damage caused by free radicals and oxidative stress.
Reduced inflammation – Soy isoflavones are anti-inflammatory and can improve various markers of inflammation in the body.
Improved immune health – Secondary to the antioxidant and anti-inflammatory properties, soy isoflavones can strengthen immune system health and function. This supplement can also reduce the symptoms of various autoimmune conditions.
Increased healthspan and lifespan – This effect hasn’t been studied directly in humans yet as the studies would be very costly and take a long time to create. However, animal studies suggest that soy isoflavones support various mechanisms associated with healthy aging and increases in lifespan and healthspan, such as autophagy, anti-senescence mechanisms, SIRT1 signaling, AMPK signaling, and NF-κB signaling.
Possible side effects
The side effects below are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to very high doses.
Soy intolerance or allergy – Some people cannot digest soy properly due to an intolerance. In some individuals, soy protein may cause an allergic reaction, which can be more severe. If you don’t know how well you tolerate soy, start with a small dose and increase it gradually if you do not notice any side effects that would imply intolerance or allergy.
Reduced testosterone levels – Extremely high doses (many grams at once) could reduce testosterone production. This side effect is often exaggerated and practically irrelevant as regular or even high doses within a reasonable range should have no impact on testosterone levels.
Nausea – This side effect is most common when people take the supplement on an empty stomach.
Diarrhea – You can usually prevent diarrhea or stomach discomfort by taking this supplement with a meal.
Toxicity – While acute toxicity is extremely rare, taking high amounts of this supplement could lead to chronic toxicity and cause health problems over time. Regularly taking high doses can also cause the body to develop a tolerance to the supplement. To prevent chronic toxicity or the buildup of tolerance, staying below 500 mg in a day is best unless you have a great reason to take more.
Contamination – Contaminated supplements are uncommon in the USA and other well-regulated countries. However, if you wish to buy products from China, India, or other countries without strict regulations, beware that the supplements may be contaminated. Either way, you need to choose the brand you order from wisely. Always read through some reviews for the specific product before you buy it. The FDA (Food and Drug Administration) has the power to regulate dietary supplements but can only do so after they have been on the market for a while. That’s because supplement companies are not obligated to announce to the FDA when releasing a new product. The FDA has to discover the product and test it for potential impurities, which can take a lot of time. During that time, the supplement can be sold on the market even if it’s impure. Also, supplement companies can change their manufacturers without announcing it to the FDA.
Who should not take soy isoflavones?
You should probably avoid taking soy isoflavones if you:
are allergic to soy
experience a severe adverse reaction after taking the supplement
are pregnant or breastfeeding (while it can be safe to take this supplement during pregnancy or breastfeeding, it can put some unnecessary risk to the child)
Who will benefit the most?
You should consider taking the supplement if you:
wish to improve general health
have a high budget for supplements and are willing to experiment with a variety of them (assuming you don’t fall into any of the categories that should avoid this supplement, soy isoflavones are relatively safe and unlikely to do more harm than good for most people)
How much soy isoflavones should you take?
The sweet spot dose typically ranges between 80-200 mg daily for most people. This amount should provide most of the benefits without meaningful side effects.
The higher end of this range usually provides slightly more benefits in the short term. If you plan to take this supplement for a longer time (multiple months or years), the lower end is probably a better way to go since it is safer, and you would develop tolerance faster if you were to take higher doses.
The upper safety limit for this supplement is not well-established. To stay on the safe side, don’t take more than the recommended dose unless you have a great reason to do so. Higher amounts may cause problems if you take the supplement for a prolonged period.
Like most other supplements, it is best to cycle soy isoflavones and take about two days off weekly to reset your tolerance. That will allow you to keep getting the benefits in the long term.
Best time to take soy isoflavones
Soy isoflavones are fat-soluble, so you should always take them with food or a dietary source of fat to absorb them well.
Whether you take the supplement in the morning or the evening does not make much difference. Both options are fine so feel free to experiment.
Interactions
Resveratrol Genistein, one of the main soy isoflavones, is highly synergistic with resveratrol for reducing adipose tissue.
Astaxanthin This combination works synergistically for improving skin health.
Tea The combination likely leads to a greater AMPK activation, which may have a positive effect on increasing healthspan and lifespan.
Coffee This combination can also lead to an increase in AMPK signaling.
Where to buy soy isoflavones?
In most countries, Amazon is the best option for ordering soy isoflavone supplements. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the Internet.
Some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.
FAQ
Like most other supplements, it is best to cycle soy isoflavones and take a break from them for about two days per week to reset your tolerance back to baseline. That will keep your body sensitive to the supplement and allow you to keep getting the benefits in the long term.
All of these options are fine. The two most important things to consider are the price and dosing. Powders are almost always the cheapest form. However, you may need a highly accurate scale to dose them correctly (preferably 0.001g). You can get one for as little as $20 from Amazon. Dosing the powders also takes time which can add up over months or years. The disadvantage of capsules is that they are often made of bovine gelatine, which rarely comes from ethical sources.
The supplement by itself should not worsen your sleep quality in any way. However, it’s best to take it with food, and you generally don’t want to eat any food right before bed as it could worsen your digestion and sleep quality.
This supplement should not become harmful once it exceeds the expiration date. However, it can lose potency over time. Keep this supplement in a cold, dark, and dry place so it remains as potent for many months or even years.
While acute toxicity is rare, taking very high amounts of this supplement could lead to various problems over time. High doses can also make you develop tolerance much faster than lower doses.
While you could safely take higher doses, there is usually no point in taking more than 200 mg daily. This amount should give you most of the benefits without meaningful side effects.
The half-life of soy isoflavones Genistein and Daidzein in the body is about 10 hours. This supplement gets metabolized within two days after you consume it. However, most of the effects of this supplement are cumulative, so they mainly happen in the long term rather than acutely. Therefore, the half-life of this supplement isn’t very relevant in practice.
In the long term, you must take the supplement for about 2-4 weeks to begin noticing most of the benefits.
Yes, soy isoflavones are vegan-friendly. If you buy the supplement in a capsulated form, beware that the capsules often contain animal-based gelatin. Instead, find a brand that puts its products into cellulose capsules.
No, they do not. The supplement should not interfere with fasting in any significant way. However, you still want to take the supplement with food as it will absorb better.
References
Most of the information in this guide is based on scientific research that can be found and verified in the PubMed medical library. We highly encourage you to use the library to verify anything you read in this article. We excluded from consideration studies that are either confounded or have a high conflict of interest.
