Nutrition Library: Nutrition During Pregnancy
All About Eating For Two, Part One
"Pickles and ice cream" conjures up a picture of a woman whose pregnancy has caused her food preferences to become a bit offbeat.
Although the tastes of mothers-to-be usually run along far more normal lines, the "pickles and ice cream" image is accurate in portraying the food cravings--and aversions--that sometimes accompany pregnancy. These tastebud changes often reflect changes in nutritional needs.
Such changes are partly due to the nourishment demands of the fetus and partly to other physiological variations that affect absorption and metabolism of nutrients. These changes help insure normal development of the baby and fill the subsequent demands of lactation, or nursing.
Exactly how nutrients are exchanged between mother and fetus is not understood. In the past it was viewed as a host-parasite relationship, with the fetus in the role of the parasite, taking whatever nourishment it required from the host mother. But recent research has shown that the fetus is not a perfect parasite. The fetus is sometimes more affected than the mother by lack of nourishment, and there is a relationship between maternal weight gain and growth and development of the fetus.
Pedro Rosso, M.D., of Columbia University's Institute of Human Nutrition, wrote in Nutritional Disorders of American Women that "contrary to the idea of fetal parasitism, there seem to be feedback mechanisms operating in the mother that would reduce the maternal supply line to the fetus when nutrients are in short supply."
Writing in Nutritional Impacts on Women, two English researchers, Frank E. Hytten, M.D., and Angus Thomson, said that changes in nutritional needs in pregnancy appear to be related to the body's adaptation to pregnancy because the changes occur too early to be responding solely to fetal needs. Such changes include a reduction of electrolytes, proteins, glucose, vitamin B-12, folate, vitamin B-6, and a rise in lipids, triglycerides, and cholesterol in blood.
The consequences of maternal malnourishment may include health problems for the mother and an infant of low birth weight who may have nutritional and other deficiencies.
Nutrients for the fetus come from the mother's diet, stored nutrients in the mother's bones and tissues, and synthesis of certain nutrients in the placenta. The placenta facilitates the transfer of nutrients, hormones, and other substances from mother to fetus.
According to a booklet by Rosly B. Alfin-Slater, Ph.D., titled Nutrition and Motherhood, if the mother is poorly nourished, the placenta does not perform its functions as well.
The Food and Nutrition Board of the National Academy of Sciences specifies certain increases in the Recommended Daily Dietary Allowances (RDAs) for pregnant and lactating women. More iron is needed not only because of fetal demands, but also because the mother's blood volume may be increased as much as 30 percent. Because the additional requirement for iron cannot be met by the usual American diet nor by existing stores in many women, iron supplements of 30 to 60 milligrams under supervision of a health-care professional are recommended.
The main effect of inadequate iron during pregnancy is iron deficiency anemia, which makes the mother less able to fight off an infection and less able to tolerate hemorrhaging during childbirth. It has been suggested that pica, the craving for substances with little or no nutritional value, may be associated with iron deficiency. Although pica occurs during pregnancy in a number of ethnic groups and geographic areas, in this country it is most prevalent among southern blacks. The most common substances eaten are dirt, clay, starch, and ice. The National Research council has noted that as many as 75 percent of th pregnant women attending southern health department clinics consumed starch and 50 percent ate clay.
Concerns about the practice are several. First, eating these substances may take the place of eating nutritionally adequate food. Second, some pica substances, such as starch, are high in calories and may contribute to obesity. Third, some pica substances (such as charcoal, air fresheners, and mothballs) contain toxic substances. Fourth, the chemical makeup of some these substances (such as charcoal, air fresheners, and mothballs) contain toxic substances. Fourth, the chemical makeup of some of these substances interferes with the absorption of minerals. Although it is not known whether anemia is the cause or the effect of pica, the craving abates when the anemia is corrected.
To a certain extent, Mother Nature lends a hand in pregnancy by improving iron absorption. A woman who is not pregnant absorbs about 10 percent of the iron present in food consumed. A pregnant woman, however, can absorb up to twice as much. In addition, the fetus stores iron during the last month or two of gestation. Some good sources of iron are meat (especially liver and other organs), egg yolks, and legumes.
Pregnancy doubles a woman's need for folate (folic acid or folacin). However, there is not universal agreement on the necessity of folate supplements for all pregnant women. Women can get additional folate by eating more green leafy vegetables, certain fruits, and liver and other organ meats. Severe folate deficiency can result in a condition called megaloblastic anemia, which occurs most often in the last trimester of pregnancy. In this condition the mother's heart, liver and spleen may become enlarged, and the life of the fetus may be threatened.
Because folic acid is crucial to cell multiplication, the fetus's needs are met before those of the mother. Therefore, the mother's health is more adversely affected at first. In contrast to the increased absorption of iron in pregnancy, folic acid absorption may be impaired by hormonal changes in pregnancy.
Pregnant women also have an increased need for vitamin B-6 and B-12. B-6 requirements usually can be met by eating more whole grains, milk, egg yolks, and organ meats. Vitamin B-12 is found in foods of animal origin, including eggs and milk products. Because B-12 occurs only in such foods, vegetarians who eat no eggs or cheese (vegans) should ask their health-care professionals about the necessity of B-12 supplements. Severe vitamin B-12 deficiency in pregnancy is rare.
A word about using vitamin and mineral supplements in pregnancy: If Taken, they would be at about RDA levels. Large doses of vitamins and minerals should be avoided. In animal studies, megadoses of vitamins A and D have resulted in fetal defects. The same is likely to be true in humans.
Pregnant adult women need an extra 400 milligrams of calcium daily. That's about 50 percent more than recommended for women 25 and older. Nearly all of the extra calcium goes into the baby's bones. This need can usually be met by consuming more dairy products. If there is not enough calcium in the mother's diet, the fetus may draw calcium from the mother's bones. Calcium deficiency in pregnancy may result in osteopenia (decreased bone density) in the mother.
Nature also helps supply the extra calcium needed in pregnancy by improving calcium absorption. Less is lost in urine and feces, and passage of calcium through the placenta to the fetus is facilitated.
A pregnant woman needs three or more servings of milk or other dairy products a day to get 1,200 milligrams of calcium. For women who are lactose intolerant, there area variety of low-lactose and reduced and reduced-lactose food products available. Sometimes calcium supplements are recommended by a woman's doctor. But pregnant women should not take calcium supplements such as bone meal and dolomite. FDA surveys have shown that some bone meal and dolomite products contain substantial amounts of lead. Lead can be harmful to both mother and fetus. Attit
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