Soy is a legume (bean).
Soy products like Tofu, Tempeh are relatively lower in Carbs.
However, soy also contains phytate, lectins and isoflavones which may cause digestive issues.
Soy is also one of the richest sources of phytoestrogens, these compounds interact with estrogen receptors in your body and may cause hormonal imbalances.
Further, Soy is Goitrogenic, it interferes with iodine absorption.