Soya

Studies in people

• No harm found

  Male hormone levels²

  A large review found that eating soy did not change testosterone or estrogen levels in men.

• Benefit

  Muscle strength and size³

  Soya protein builds muscle and strength just as well as whey when combined with weight training.

• Open question

  Muscle building and hormones⁴

  Soya protein builds lean muscle about as well as whey, but its effect on testosterone is still unclear.

• No harm found

  Plant protein for meat-free diets⁵

  Well-processed soya protein can replace meat and fish protein in adults without hurting how they use dietary nitrogen.

• Open question

  Memory and thinking⁶

  Some studies link eating more soya to better thinking, but others disagree, so it is still unclear.

• Benefit

  Obesity risk in adults⁸

  In Chinese adults, those eating more soy isoflavones from soya foods were less likely to be obese.

• No harm found

  Menopause symptom relief⁹

  In women eating soy powder daily, higher soya phytoestrogen levels in blood and urine did not mean fewer hot flushes.

• Benefit

  Heart health in diabetes¹⁰

  In Chinese adults with diabetes, eating soya more often was linked to fewer deaths from heart disease.

• Open question

  Iron absorption from infant formula¹¹

  In women, iron was absorbed less from soya-based infant formula than from milk-based formula.

Animal and lab studies only

• No harm found

  Gut bacteria and food additive¹⁷

  Soya hemicellulose is broken down by gut bacteria, and animal studies found no bad effects at high doses.

• Benefit

  Gut inflammation¹⁸

  In animal studies, soya isoflavones eased gut inflammation and helped the gut lining work better.

• Benefit

  Bone loss after menopause¹⁹

  In animal studies, soya isoflavones combined with DHA reduced bone-breaking cell formation, but scientists do not yet know if this helps people.

Study type not stated

• Open question

  Weight and blood sugar¹³

  Soy isoflavones in soya may help with weight and blood sugar, but scientists do not yet know whether they truly work.

• Open question

  Gut health¹⁴

  Soy foods like fermented soy milk may help gut health, but scientists do not yet know about newer soy proteins.

• Benefit

  Blood sugar control¹⁵

  Fermented soya foods like natto and miso may help with blood sugar, but scientists are still studying how.

• Concern

  Removing allergens by heat¹⁶

  Some raw soy sauces still hold soybean allergens, but heat-treating and filtering soy sauce removes them.

Found in some samples or products

These come from where it was grown, how it was processed or cooked, or what it was made into. They are not about the ingredient itself, so the signal does not count them.

• Heavy metal in food⁷

  Soy foods like tofu and tempeh can carry cadmium, a heavy metal; vegans eating the most soy took in the most.

How it’s made and used

• How much the body absorbs¹²

  In people, soya isoflavones from fermented soybean biscuits were absorbed and passed out in urine faster than from plain soybean biscuits.

• Yoghurt bacteria levels²⁰

  Adding soybean peptides to yoghurt kept more live bacteria in it during storage, with no change in taste.

The signal at the top counts the findings in people and in animal and lab studies. A concern in studies of people outranks animal and lab studies, and “No concerns” needs at least one finding in people. When most findings in people point one way, the page leans that way (“Mostly”), and every finding is still shown. Findings whose study type is not stated are shown but not counted. This page is a reference, not medical advice. It describes what regulators and published research say. Talk to a doctor or dietitian about your own diet.