Not always. Common kitchen advice requires some clarification here. Saponins and similar substances may decrease via cooking, soaking and draining, yet the visible foam does not accurately indicate the level of unwanted compounds remaining in the dal.
A 2017 study in ScienceDirect showed that processing and cooking can reduce saponins in pulses. The authors added that saponins occur naturally in edible legumes and their impacts are more complex than simply calling them harmful.
