Surely every pregnant woman has had the same thought as she worships at the porcelain altar: there has got to be some reason for morning sickness. Now a controversial new book argues that there is--and that pregnant woman ignore that reason at their fetus's peril. In "Protecting Your Baby-To-Be: Preventing Birth Defects in the First Trimester" (240 pages. Addison-Wesley. $20), biologist Margie Profet claims that the food aversions and nausea that many mothers-to-be suffer evolved to keep them from eating things that could be toxic to the fetus. Pungent foods such as brussels sprouts, broccoli, onions, spices, coffee and chocolate, Profet says, nauseate some pregnant women because they contain compounds, such as allyl isothiocyanate in cabbage, that can interfere with fetal-organ formation.
Unfortunately for this appealing idea, "There is no evidence that these foods contain toxins in amounts that would cause birth defects," says Dr. Richard Johnston of the March of Dimes. So why is there morning sickness? Hormonal changes alter blood vessels from the nose to the gastrointestinal tract, making women sensitive to smells and subject to nausea. "It seems plausible that food aversions are side effects of these hormone changes," says Johnston. "There's no need to suppose that [morning sickness] confers an evolutionary advantage." Or that if you eat cabbage while pregnant your baby will be deformed.