Morning sickness, the nausea, vomiting and sudden aversions to certain foods that affect up to 80% of pregnant women, may be more than an unpleasant side effect. A new study from UCLA suggests these symptoms are part of a healthy immune response that helps protect both mother and baby.
Published in Evolution, Medicine and Public Health, the research connects food-related symptoms of early pregnancy to shifts in immune system signaling. By analyzing blood samples from 58 Latina women alongside questionnaires about nausea and aversions, the team found that women who reported stronger symptoms also showed a more pro-inflammatory immune balance.
That immune shift may serve a protective purpose: keeping the fetus safe while encouraging behaviors that minimize exposure to harmful foods. Participants most often reported aversions to tobacco smoke and meats, items that, historically, posed higher risks of infection or toxins.
“Nausea, vomiting or aversions to foods or smells are not indications that something is going wrong for the mother or the fetus,” said coauthor Daniel Fessler, Ph.D., professor of anthropology at UCLA. “It’s likely an indication that everything is moving along normally, and a reflection of the body’s healthy and helpful immune response.”
The findings support a long-standing evolutionary theory: that food aversions and nausea steer pregnant women away from substances more likely to cause harm at a stage when the fetus is most vulnerable. Today, those instincts echo modern warnings on certain foods like undercooked meat, soft cheeses and unpasteurized products.
While more research is needed, the study’s authors say the results could help reduce stigma and encourage practical workplace accommodations for pregnant women. Recognizing morning sickness as a normal, biologically adaptive process may shift how it’s understood both in medicine and society.
The study was supported by the U.S. National Institutes of Health.