The Mystery of Pregnancy Cravings
Why do ice cream and pickles hit the spot?
Have you ever heard stories of pregnant women craving pickles and ice cream? Or seen the media portraying pregnant women demanding that their partners get Ben and Jerry’s ice cream at 3am? Such anecdotes become more outlandish – pregnant women fighting in Trader Joe’s over the last box of multi-grain waffles, losing control at the smell of chocolate, and driving through hailstorms to get curly fries. As we cross cultural boundaries, the specifics of the stories change, but cultures almost universally offer some sort of explanation as to why cravings exist and legitimize the occasional bizarre craving behavior.
When Queen Jane Seymour became pregnant in 1537, King Henry VIII did not have a male heir to the throne since his two previous wives had been unable to bear children. With a vested interest in the stability of Jane’s pregnancy, Henry went to great lengths to import live quail from France in order to satisfy the Queen’s cravings, since tradition stipulated that satisfied cravings made for safer pregnancies. This grand gesture seemed to pay off, as future heir Edward VI was born later that year. However, in a strange twist of fate, Jane died twelve days later. Rumor had it that her extravagant cravings had caused her death.
Why should science concern itself with in pregnancy cravings? From the perspective of advancing knowledge, we simply do not know what causes pregnancy cravings. Societies have furnished causal explanations that made sense within their cultural context for millennia. However, science has had difficulty evaluating these claims since a craving cannot be easily quantified or measured. From a more practical standpoint, being able to study cravings scientifically would allow us to better understand the state of the body during pregnancy and offer nutritional guidelines that may improve maternal diets.
Historical Interpretations: Humors and Juices
Pregnancy cravings have long been accepted as a natural part of pregnancy. In the second century AD, renowned Greek physician Soranus authored Gynecology, a work that remained influential until the 16th century and continues to have a cultural impact today. Soranus believed that there were three stages of pregnancy: preservation of the injected seed, pica (cravings for non-food substances), and perfection of the embryo.1,2 In the second stage, he described women as having a “want of appetite sometimes for all, sometimes for certain foods; appetite for things not customary.”2
““Bad liquids” were thought to cause pregnancy cravings.
In medieval times, famed rabbi, physician, and philosopher Maimonides adopted the existing Greco-Roman theory that cravings were the result of an imbalance in bodily humors – fluids thought to influence a person’s physical and mental qualities. Women harbored “bad liquids” in the folds of their stomach from their failure to release menstrual blood during conception. When these liquids penetrated the stomach, a woman would crave sour and pungent things until these unpleasant juices were eliminated by vomiting. As the pregnancy progressed and the growing fetus reduced penetration of these liquids, women would be less susceptible to cravings and nausea.3
Cross-Cultural Interpretations: Dohada and Tsango
These early theories grew out of a need for physicians to interpret the visible symptoms of pregnancy, and their influence remains apparent today. In the Hindu culture, the essence of pregnancy cravings is encapsulated in the very word for pregnancy cravings, dohada, which means “two-heartedness.” It attributes pregnancy cravings to the “presence of a second heart and a second will in the body of the mother.” As such, “the prosperous development of the embryo depends on the satisfaction of these cravings, in whatsoever manner they may manifest themselves.”4
In Kenya, it is thought that the tsango, an agent of health present in the bodies of women, is essential for life, digestion, and reproduction.5 When a woman becomes pregnant, the tsango looks after the baby, watching over the provision of food from the mother to the child, and ensuring that the blood carrying the food is good and clean. Kenyan culture does not specify what a woman should do regarding her cravings, but it does demand that she balance her food intake so as to prevent the tsango from becoming too strong or too weak, both of which are injurious to her health and her child.
Western Interpretations: Body’s Wisdom
The Western approach to pregnancy cravings leans heavily on the idea of the “wisdom of the body.” Cravings are thought to be a Darwinian mechanism to meet the body’s demand for certain nutrients.6,7,8 Based on this belief, a pregnant woman sending her husband out for a late night trip to get ice cream might justify her craving by saying that her body “needs calcium.” In truth, however, the evidence for this statement is weak. While studies have seen associations between certain cravings and maternal diet deficiencies (e.g. when women crave clay to fulfill an iron deficiency), researchers are uncertain about the causal direction; did the deficiency occur because of abnormal eating habits, or did the craving occur because of the deficiency? 9,10
Medical Interpretations: Hormones and Orexigenic Agents
With advances in the sciences, we can begin to bridge the gap between culture and scientific theory using the physiology behind pregnancy cravings. During pregnancy, women are resistant to leptin, an endocrine growth factor. Leptin reduces appetite and stimulates metabolism by interacting with receptors at the “appetite center” of the hypothalamus.11,12 Without leptin, multiple orexigenic pathways, or pathways that stimulate hunger, are left unopposed.13,14 This causes neuropeptide Y, one of the most potent orexigenic agents known, to have significantly decreased immunoreactivity during pregnancy, and this is thought to contribute to increased food intake.
“Neuropeptide Y increases hunger.
Studies have also been performed to understand women’s changing sense perception during pregnancy. Some of the first signs of pregnancy include “increased sensitivity to odors” and “a metallic taste in your mouth.”15 Abnormal smell and/or taste perception is reported in roughly 75% of women.16 It has been hypothesized that these altered gustatory and olfactory thresholds are caused by a change of neuronal activity within the female brain. Because of uterine expansion during pregnancy, adjacent uterine and gustatory neurons may be interacting with one another.17 In any case, cravings appear to be affected by smell and taste sensitivity, and thus have a direct biological basis.18
Challenges for Research
While science has shown that the physiological changes accompanying pregnancy cravings have a neuronal and hormonal basis, it has yet to offer a strong theory as to how these cravings have come about. Is the Western notion of causality due to “wisdom of the body” valid? In order to determine if Queen Seymour’s cravings were a result of a nutritional deficiency, it would by hypothetically necessary to establish that (a) she had such a deficiency (b) quail had a nutrient that satisfied it and (c) the deficiency preceded her consumption of quail, so as to exclude reverse causation. Since this question involves a human subject whose cravings cannot be manipulated in a laboratory setting, population-based nutritional epidemiology may hold the answer.
“Nutritional epidemiology may hold the answer to our craving questions.
I am applying the conceptual methodology outlined above to my current thesis project. In order to measure a nutritional deficiency (part a), I could theoretically use biochemical blood or tissue indicators to measure the amounts of various nutrients in the blood. However, analyzing these biochemical indicators on a large scale would require expensive blood analyses, and some nutrients such as total fat have no indicators. Thus, nutritional epidemiologists utilize noninvasive instruments like food records and dietary journals to calculate the consumption of nutrients based on what food was eaten. In order to find out if the food craved contains the nutrient (part b), its nutrient profile would be determined from nutritional databases. Finally, the deficiency must precede the craving in order to determine a causal relationship (part c).
While we do not yet know the mechanisms that led to Queen Jane’s cravings, comparative cross-cultural studies have shed insight on the myriad of causal interpretations offered. Advances in nutritional epidemiology also hold promise for assessing the validity of the “wisdom of the body” hypothesis, which would lead to better nutritional guidelines regarding maternal diets. Until then, it’s probably best to satisfy that craving for quail!
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10Lopez, L. B., Langini, S. H., & Pita de Portela, M. L. (2007). Maternal iron status and neonatal outcomes in women with pica during pregnancy. International Journal of Gynaecology and Obstetrics: The Official Organ of the International Federation of Gynaecology and Obstetrics, 98(2), 151-152. doi:10.1016/j.ijgo.2007.03.038
11Bajoria, R., Sooranna, S. R., Ward, B. S., & Chatterjee, R. (2002). Prospective function of placental leptin at maternal-fetal interface. Placenta, 23(2-3), 103-115. doi:10.1053/plac.2001.0769
12Keim, N. L., Stern, J. S., & Havel, P. J. (1998). Relation between circulating leptin concentrations and appetite during a prolonged, moderate energy deficit in women. The American Journal of Clinical Nutrition, 68(4), 794-801.
13Oberto, A., Mele, P., Zammaretti, F., Panzica, G., & Eva, C. (2003). Evidence of altered neuropeptide Y content and neuropeptide Y1 receptor gene expression in the hypothalamus of pregnant transgenic mice. Endocrinology, 144(11), 4826-4830. doi:10.1210/en.2003-0197
14Brennan, A. M., & Mantzoros, C. S. (2006). Drug insight: The role of leptin in human physiology and pathophysiology–emerging clinical applications. Nature Clinical Practice. Endocrinology & Metabolism, 2(6), 318-327. doi:10.1038/ncpendmet0196
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17Persinger, M. A. (2001). Shifting gustatory thresholds and food cravings during pregnancy as expanding uterine-induced steady potential shifts within the insula: An hypothesis. Perceptual and Motor Skills, 92(1), 50-52.
18Tierson, F. D., Olsen, C. L., & Hook, E. B. (1986). Nausea and vomiting of pregnancy and association with pregnancy outcome. American Journal of Obstetrics and Gynecology, 155(5), 1017-1022.