Are BCAA supplements safe during pregnancy?

What does the evidence say about BCAA supplements during pregnancy?

1. In a mouse study, supplementing isoleucine, a BCAA, at levels mimicking athletic-style supplementation during early pregnancy disrupted the normal relationship between fetal and placental weight and led to a 60 percent greater rate of ruptured amniotic membranes. 1
2. In human pregnancy research, higher blood levels of valine, leucine, and isoleucine in early pregnancy were associated with a markedly higher risk of gestational diabetes, with odds roughly 1.8 to 2 times higher when comparing the highest to the lowest levels. 2
3. Many dietary supplements, BCAA products included, have not been tested in pregnant women, and outside a few specific categories the FDA does not review a supplement's safety before it reaches the market. 3
4. A recent review of the pregnancy and postpartum supplements with the strongest supporting evidence, covering folic acid, iron, vitamin D, calcium, iodine, omega-3 fatty acids, and choline, does not include BCAAs among them, reflecting how little established pregnancy guidance exists for this category. 4
5. The authors of the mouse isoleucine study noted that other unintended effects of BCAA consumption deserve more thorough study given how common BCAA use has become among athletes, and flagged possible longer-term metabolic consequences worth further research. 1

Is BCAA supplements safe in each trimester?

• First trimester. First-trimester placental development is exactly the window where the mouse research raises concern, since that study supplemented a BCAA during the earliest days of pregnancy and found lasting effects on the fetal-placental relationship. This is a reasonable trimester to skip a BCAA supplement.
• Second trimester. Blood sugar screening for gestational diabetes typically happens in the second trimester, and this is also when the observational link between higher BCAA levels and gestational diabetes risk becomes most relevant to keep in mind if you are weighing a supplement.
• Third trimester. No third-trimester-specific BCAA research exists, pregnant or not. If you are using BCAAs for workout recovery, whole-food protein is a better-studied way to meet the same goal this late in pregnancy.