Soya isoflavones
Soya isoflavones in tablets and capsules, plus soya lecithin. We explain the difference between extract weight and pure isoflavones on the label, which form suits you and what soya can realistically do.Read more →
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Soya isoflavones: forms, label strength and honest expectations
Soya is a bean, and most people buy it for one group of plant substances: isoflavones. The three main ones are genistein, daidzein and glycitein. Isoflavones are phytoestrogens, which means their structure resembles the body's own oestrogen, so they can attach loosely to the same receptors. Loosely is the important word, because the effect is much smaller than that of a hormone. Tofu, edamame and miso deliver them too, but in far smaller amounts than a concentrated extract. Within our wider herbal and plant range, soya sits with the plant extracts that people use over longer periods.
The number on the pack is often not the isoflavone amount
This is where soya buying goes wrong. Some labels state the weight of the soya extract, others the amount of pure isoflavones. A tablet with 250 mg extract standardised to 40 percent isoflavones gives you 100 mg isoflavones. A tablet stating 250 mg extract with no percentage may give a fraction of that. Two packs that look identical can differ several times over in what they actually deliver. Studies in menopausal women mostly worked with 50 to 100 mg isoflavones a day, so that is the range worth comparing against.
Forms you will find in this collection
- Standardised extract in tablets or capsules: concentrated, and the only form that lets you compare milligrams of isoflavones directly.
- Fermented soya extract: fermentation already converts part of the isoflavones, which the body takes up more easily, so the labelled amount is often lower.
- Soya lecithin: made from the fat fraction of the bean, rich in phospholipids and choline, with barely any isoflavones. If that is what you are after, look at our lecithin products instead.
How we select soya supplements
With soya we judge three things: the form, the dose and whether the label is clear about which of the two numbers it shows. We prefer extracts that state milligrams of isoflavones, because that is the only figure you can compare between brands. We stock non-GMO soya where the brand can document it, and we leave out products whose percentages we cannot verify. We also do not promise relief of menopausal complaints. The European food safety authority (EFSA) has approved no health claim for soya isoflavones, and we would rather tell you that than suggest more. You can read how we choose brands and products.
Who soya suits and what to expect
Most buyers are women in the years around the menopause, often after stopping or deciding against hormone therapy. Whether soya does anything for you depends partly on your gut bacteria: only some people convert daidzein into equol, the more active form, which helps explain why experiences differ so much. Others simply want a plant source of isoflavones alongside a diet with little soya in it.
Be patient and realistic. Any effect builds over weeks, not days, so judge it after two to three months of daily use at a consistent dose. Soya is a declared allergen in the UK, so it is not suitable with a soya allergy. EFSA also notes that isoflavones can interfere with thyroid hormone production, so speak to your GP first if you take thyroid medication, are pregnant or breastfeeding, or have a hormone-sensitive condition. If you would rather try a different isoflavone profile, red clover extracts are the usual alternative, and our menopause collection brings together the other options women combine with it.
Frequently asked questions
What are soya isoflavones?
Soya isoflavones are plant substances from the soybean. The three main ones are genistein, daidzein and glycitein. They are called phytoestrogens because their structure resembles the body's own oestrogen closely enough to attach loosely to the same receptors, though the effect is far weaker than a hormone. Soya foods such as tofu, edamame and miso contain them naturally. Supplements use a concentrated extract, so one tablet can hold much more than a normal portion of soya food.
How much isoflavone is actually in a soya supplement?
Less than many labels suggest. Packs either state the weight of the soya extract or the weight of the pure isoflavones, and the two are very different. An extract standardised to 40 percent isoflavones delivers 100 mg isoflavones from 250 mg extract. Without a percentage on the label you cannot know. According to EFSA, supplements for women around the menopause typically supply between 35 and 150 mg isoflavones a day. Compare that figure, not the extract weight.
Which form of soya should I choose?
It depends on whether you want isoflavones or the fat fraction of the bean. Standardised extract gives you a number you can compare, fermented extract is absorbed more easily, and lecithin is a different product altogether.
| Form | Typical daily isoflavone amount | Suits |
|---|---|---|
| Standardised extract, tablet | 35 to 150 mg | A clear, comparable dose |
| Fermented extract, capsule | 35 to 150 mg | Easier absorption |
| Soya lecithin | Negligible | Phospholipids and choline |
When is the best time to take soya isoflavones?
With a meal, and at the same time each day. Food slows the passage through the stomach a little and reduces the chance of mild digestive discomfort, which is the most commonly reported complaint. Some brands suggest splitting a higher amount into a morning and evening dose, which keeps levels steadier through the day. What matters most is consistency: isoflavones do not build up in the body, so a daily habit at a fixed dose beats an irregular high dose.
How long before I notice anything?
Longer than most people expect. Research in menopausal women ran for three months or more, and part of the effect appeared only after several months of daily use. Plan for at least eight to twelve weeks at the same dose before you decide whether soya is doing anything for you. If you stop after two weeks, you have not really tested it. Keep in mind that results in studies were mixed, so a clear personal effect is not guaranteed.
Can men take soya isoflavones?
Yes, soya isoflavones are not a women-only product, and soya foods are eaten daily by men across large parts of Asia. Most concentrated supplements are marketed at women around the menopause, so the labelled dose is aimed at that group. If you are a man mainly interested in soya as part of your diet, whole soya foods or soya protein make more sense than a high-dose isoflavone extract. Discuss it with your GP if you take hormone-related medication.
Why do soya isoflavones seem to work for some people and not others?
Gut bacteria explain part of it. Daidzein, one of the soya isoflavones, can be converted in the gut into equol, a more active substance. Only some people carry the bacteria that do this, and the proportion is higher in populations with a traditionally soya-rich diet. Non-converters take in the same isoflavones but end up with less equol. That is one reason study results are mixed, and it is why we never present soya as a predictable outcome for everyone.
Are there situations where soya isoflavones are not suitable?
Yes. Soya is one of the allergens that must be declared on UK labels, so avoid these products with a soya allergy. EFSA reviewed isolated isoflavones in supplements for peri- and post-menopausal women and found no evidence of harm at the doses and durations studied, but it also notes that isoflavones can interfere with thyroid hormone production. Speak to your GP first if you take thyroid medication, use hormone therapy, are pregnant or breastfeeding, or have a hormone-sensitive condition.
