Is soy milk safe during pregnancy?

What does the evidence say about soy milk during pregnancy?

1. Soy drinks average about 37.8 g of protein per kilogram, exceeding cow's milk at 32.6 g, and soy is the only plant-based drink category to clear 3 percent protein. 1
2. The biological effects of soy isoflavone exposure are described as controversial and inconclusive in humans, and reviewers note it is unclear whether negative findings from animal models can be extrapolated to people. 2
3. In a prospective cohort of 224 pregnant women, daily soy intake below 40 g was associated with roughly double the risk of gestational diabetes after adjustment for confounders. 3
4. Swapping cow's milk for a soy drink that is not fortified with riboflavin was modelled to raise the share of women with inadequate riboflavin intake, showing that fortification rather than the plant decides the nutritional outcome. 4
5. Pregnancy requires 220 mcg of iodine and 2.6 mcg of vitamin B12 daily, and people on vegetarian or vegan diets are advised to check with a provider about whether supplementation is needed. 5

Is soy milk safe in each trimester?

• First trimester. The isoflavone question is what sends people searching, and the honest summary is that findings in humans are mixed and inconclusive, while the alarming results come largely from animal models researchers say may not extrapolate to people. Ordinary soy foods and soy milk are a different exposure from concentrated isoflavone supplements, which are the ones worth avoiding.
• Second trimester. Soy milk is the only plant milk with protein comparable to cow's milk, which makes it the most useful swap if you have moved away from dairy. One cohort found lower soy intake associated with higher gestational diabetes risk, which at minimum argues against cutting soy out on principle.
• Third trimester. Nothing about late pregnancy changes soy milk. Check the carton for added calcium, vitamin D, and B12, since soy milk is not automatically fortified and iodine in particular is rarely added. If soy milk is doing the work dairy used to do, confirm the gaps are covered.