Immunosuppression during pregnancy makes the mother vulnerable to pathogens. Because meat is the principal source of ingestible pathogens, pregnancy raises the costs of meat eating. Natural selection has crafted a mechanism involving changes in nausea susceptibility and olfactory perception that reduces meat consumption during pregnancy. Evidence is presented showing that the luteal phase is marked by both immunosuppression and changes in nausea susceptibility and olfaction; meat consumption may be reduced during this period, suggesting a mechanism similar to pregnancy sickness.
Constraints on compensatory increases in meat consumption outside of the luteal phase explain why women eat less meat than men. Meat is the principal target of acquired aversions. Women possess more aversions than men,suggesting that prophylactic mechanisms sometimes result in longstanding dietary changes. Reproductive immunosuppression explains many aspects of dietary behavior and sheds light on factors that may have contributed to gender-based divisions of labor during hominid evolution.
Immunosuppression makes women vulnerable to pathogens during pregnancy. Pregnancy sickness alters behavior so as to reduce the risk of infection, principally by reducing meat intake through changes in olfaction, nausea susceptibility, and dietary preferences. The luteal phase of the menstrual cycle is a period of preparation for pregnancy. Periodicity in physiological measures, autoimmune disorders, chronic infections, and sleep disturbances indicate that immunosuppression also occurs during the luteal phase. This phase is marked by changes in nausea susceptibility and olfaction, paralleling changes during the first trimester of pregnancy. Evidence of reduced meat consumption during the luteal phase is reviewed. Because compensatory increases in meat consumption during other phases are necessarily incomplete, women are predicted to eat less meat than men. Data supporting this prediction are reviewed. Imperfect prophylactic mechanisms may result in long-standing aversions. Consistent with greater episodic vulnerability to pathogens, women report more acquired food aversions. Sex differences in aversions are matched by differences in olfaction and nausea susceptibility. Meat is the principal target of aversions, a pattern for which parallels exist in other animals. Vegetarianism, which is more common among women, is explicable as a product of meat aversion. Reproductive immunosuppression may have contributed to hominid behavioral dimorphism, setting the stage for a gender-based division of labor.
