While moderate use of soy protein powder is considered okay by most experts, an alternative source of protein may be advisable during pregnancy due to the unique properties of soy protein powder. During pregnancy, protein requirements are dramatically increased as well as macronutrient requirements. Taking supplements during pregnancy is something you should consult your medical professional about. Where possible, we would recommend trying to intake whole foods during pregnancy.
Soy protein is very high in phytic acid which is a naturally occurring substance that binds to minerals such as calcium, niacin, iron, magnesium, and zinc. This blocks the absorption of these minerals in your intestine. This is not ideal, given these minerals play an important role in your baby's development.
In addition, soy contains an anti-nutrient that inhibits the digesting enzyme called trypsin, which slows soy protein digestion. As protein intake requirements are increased during pregnancy, selecting a protein source without this inhibitor might be preferable.
Soy protein also contains isoflavones which include phytoestrogens that mimic the hormone estrogen in your body. This is an important hormone during pregnancy and some experts warn that consuming too many phytoestrogens may negatively affect your baby's development.
Animal studies have also linked high soy intake to fertility problems in females as well as increased urological defects in males. It is unknown if similar effects may occur in humans with a diet high in soy.