If You’re Eating for Two, Why Are You Vomiting?

One of the most common symptoms of early pregnancy in human beings is nausea and vomiting. Why do so many pregnant women have so much trouble keeping food down at the very time that their need for calories and other nutrients has just gone up? Why is this problem common in women but seemingly nonexistent in pregnant females of other species? Is there something wrong with the design of human pregnancy, or is there something wrong with the food the pregnant woman is eating? I’m inclined to suspect the food, especially because morning sickness is common in the United States but rare to nonexistent in societies whose staple foods all come from plants.

Vomiting is a powerful defense mechanism. It effectively removes toxins and infectious agents from the stomach and even the upper intestines. It’s nature’s way of expelling things that shouldn’t be allowed to enter the body. This defense mechanism may be particularly important during pregnancy. Studies have consistently shown that women who vomit during early pregnancy are less likely to have a miscarriage than are those who merely feel nauseated. Perhaps it’s because the vomiting prevented things that would be harmful during early pregnancy from entering the woman’s body. Thus, it’s probably no coincidence that the nausea and vomiting associated with pregnancy tend to be most severe during the first trimester, which is the most sensitive phase of development.

In a classic article, Samuel Flaxman and Paul Sherman explained how morning sickness could end up protecting the mother and the pregnancy. They argued that morning sickness is most common when the major organ systems are developing, and the vomiting seems to be triggered by the foods and beverages that are most likely to be harmful to the mother and the pregnancy. Flaxman and Sherman pointed out that in 9 out of 9 studies, women who experienced morning sickness were much less likely to miscarry.

Flaxman and Sherman noted that many pregnant women have aversions to alcoholic and nonalcoholic (mainly caffeinated) beverages and strong-tasting vegetables, but the greatest aversions were to meats, fish, poultry, and eggs. The importance of animal-based foods in causing morning sickness also became obvious in a cross-cultural comparison. Seven societies that were free of morning sickness were significantly less likely to have animal foods as dietary staples and were significantly more likely to have only plants (mainly corn) as staple foods than were 20 societies in which women experience morning sickness.

Foodborne infectious or parasitic disease could be a serious threat to the health of a pregnant woman or her pregnancy. During pregnancy, a woman’s immune system is already somewhat suppressed, to keep it from attacking the pregnancy. As a result, pregnant women are more likely to catch serious, potentially deadly infections. Infectious and parasitic diseases are also a major threat to the developing embryo. For example, if a pregnant woman catches Toxoplasma, which is a parasite found in cat droppings or undercooked beef, the parasite infection could cause miscarriage, stillbirth, or severe birth defects.

A pregnant woman can protect her health and her pregnancy by simply avoiding the foods that are likely to make her vomit. A purely plant-based diet provides all of the nutrients that a pregnant woman needs, except for vitamin D (which she can get from sunshine) and vitamin B12 (which is made by bacteria and is available in a nice, clean tablet).

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