The food cravings and aversions that sometimes accompany pregnancy aren't just motivated by hormonal fluctuations, they are due in part to your baby's nutritional demands and to physiological changes in your body that affect the absorption and metabolism of certain nutrients. These changes help insure normal fetal development and later, fulfill the demands of lactation.
During pregnancy, your natural levels of vitamin B12 and B6, electrolytes, proteins, glucose, and folate decrease; while lipids, triglycerides, and cholesterol increase. In Nutritional Impacts on Women, researchers Frank E. Hytten, M.D. and Angus Thomson wrote that changes in nutritional needs occur too early in a pregnancy to be exclusively a response to fetal needs, and instead appear to be caused by the woman's body adapting to the new pregnancy.
The food you eat, as well as nutrients that are stored in your bones and tissues and those that are synthesized in the placenta, supply your baby with all the nutrients he or she needs for growth and development. However, exactly how nutrients are exchanged between you and your baby is not well understood. In the past, pregnancy was believed to be a host-parasite relationship, with the fetus taking whatever nourishment it required from the mother. But recent research has shown that the fetus can be more severely affected by lack of nourishment than the mother. "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," states Pedro Rosso, M.D., of Columbia University's Institute of Human Nutrition.
The placenta acts as a doorway through which nutrients, hormones, and other substances are transferred from you to the fetus. According to Dr. Roslyn Alfin-Slater, Nutrition expert and author of "Human Nutrition, A Comprehensive Treatise," if the mother-to-be is poorly nourished, her placenta does not function well. In addition, her health may suffer and the baby may be born at a low birth weight and suffer growth abnormalities if deprived of essential vitamins and nutrients over a prolonged period of time.
The following are essential nutrients, vitamins, and minerals that are often affected by pregnancy. To ensure your health and that of your baby, eat a healthy, well-balanced diet and talk to your doctor about vitamin supplements. However, if you do take vitamin and mineral supplements during your pregnancy, be sure they are at RDA levels and avoid large doses of vitamins and minerals. For example, in animal studies, megadoses of vitamins A and D have resulted in fetal defects and the same is likely to be true in humans.
Iron
Iron is an essential component of proteins found in red blood cells that transport oxygen to tissues, and it is also essential for the regulation of cell growth and differentiation. Extra iron is needed during pregnancy because your blood volume increases 40 to 50 percent to support your growing fetus. A woman who is not pregnant absorbs about 10 percent of the iron contained in the food she eats; but a pregnant woman's body absorbs up to twice as much. The Recommended Daily Dietary Allowance (RDA) of iron for pregnant and lactating women is 27 mg a day. Good sources of iron include meat (especially liver and other organs), egg yolks, and legumes. However, the average American diet does not contain enough iron to meet these requirements, so many pregnant women are encouraged to take a daily iron supplement of 30 to 60 milligrams.
Inadequate iron levels can cause anemia, which decreases your ability to fight off infection and tolerate hemorrhaging during childbirth. It has also been suggested that pica, the craving for substances with little or no nutritional value (such as dirt, clay, starch, and ice), may be associated with iron deficiency. According to the National Research council, as many as 50 percent of the pregnant women attending southern health department clinics ate clay. Eating these substances may take the place of nutritionally valuable foods; and many pica substances, such as starch, are high in calories and may contribute to obesity. In addition, some pica substances (such as charcoal, air fresheners, and mothballs) contain toxic substances, which can interfere with the absorption of minerals. Although it is not known whether anemia is the cause or effect of pica, the craving abates when the anemia is corrected.
Folic Acid
Pregnancy doubles a woman's need for folate (folic acid or folacin), yet folic acid absorption may be impaired by hormonal changes during pregnancy. Repeated studies have shown that women who consume 400 micrograms (0.4 milligrams) daily prior to conception and during early pregnancy reduce the risk that their baby will be born with a serious neural tube defect (a birth defect involving incomplete development of the brain and spinal cord) by up to 70 percent. Doctors and scientists still aren't completely sure why folic acid has such a profound effect on the prevention of neural tube defects, but they do know that it is crucial in the development of DNA, cell growth and development, as well as tissue formation.
You can get additional folate by eating more green leafy vegetables, certain fruits, and liver and other organ meats. Because folic acid is crucial to cell multiplication, the fetus's needs are met before those of the mother; therefore, pregnant women are at an increased risk of folate deficiency. Severe folate deficiency can result in a condition called megaloblastic anemia, in which the mother's heart, liver and spleen become enlarged and the life of the fetus may be threatened.
B-Vitamins
Pregnant women have an increased need for vitamins B6 and B12. B12 maintains healthy nerve cells and red blood cells, and is also essential for creating DNA, the genetic material in all cells. Vitamin B6 is essential for normal brain development and function, and aids in the formation of important brain chemicals called neurotransmitters. You can usually meet B6 requirements usually can be met by eating more whole grains, milk, egg yolks, and organ meats. Vitamin B12 is found in animal foods, including meat, eggs and milk products; vegetarians who eat no eggs or dairy products and vegans should ask their health-care professionals about B12 supplements.
Calcium
Calcium is crucial during pregnancy for synthesis of fetal bones and teeth. It is also necessary for proper blood clotting and regulation of blood pressure, heartbeat, water balance in cells, and muscle contractions. If your diet does not supply sufficient calcium, the fetus will draw from reserves in your bones, which can cause osteopenia (a similar, but milder condition than osteoporosis). Fortunately, increased estrogen production during pregnancy facilitates calcium absorption.
The U.S. RDA of calcium for adult women (pregnant or not) is 1000 mg. You can achieve this by consuming three or more servings of milk or other dairy products a day. For women who are lactose intolerant, there are a variety of low-lactose or lactose-free dairy products available, or your doctor may recommend a calcium supplement. However, you should not take calcium supplements such as bone meal and dolomite, which FDA surveys have shown may contain substantial amounts of lead. In addition, do not take a calcium supplement at the same time as your prenatal vitamin-mineral supplement because iron inhibits the absorption of calcium.
Calories and Weight Gain
In the past, pregnant women were told to limit their weight gain to about 15 pounds. Excessive weight gain was thought to be related to toxemia (also called preeclampsia or pregnancy induced hypertension), a condition of unknown origin that occurs after the 20th week of pregnancy and is characterized by high blood pressure, protein in the urine, and water retention.
Although sudden large weight gain, water retention and blood pressure elevation are still recognized danger signs of toxemia, most physicians agree that weight gain does not cause toxemia. In fact, the consequences of restricted weight gain and weight loss appear to be potentially more harmful than unrestricted weight gain, particularly to the fetus, even in women who were overweight before becoming pregnant.
If a woman's calorie intake is restricted during pregnancy, she may not get enough protein, vitamins, and minerals to adequately nourish the fetus. It can also result in a breakdown of the mother's fat stores, leading to the production of ketones in her blood and urine. Ketones are produced during times of starvation, and chronic production of ketones can result in mental retardation in the fetus.
For these reasons, the National Academy of Sciences recommends that pregnant women eat approximately 300 calories more per day than they did before becoming pregnant, and gain about 25 to 35 pounds over the entire nine months. The pattern of gain is considered more important than the actual number of pounds: weight gain should be at its lowest during the first trimester and steadily increase through the second and third. You should gain the most weight in your third trimester when the fetus is developing its protective fat stores. During pregnancy, your fat deposits increase by more than one third.
Experts estimate that if you gain 25 pounds during your pregnancy, it consists of the following:
- Baby: 8 pounds
- Placenta: 1 pound
- Amniotic fluid: 1.5 pounds
- Breasts: 3 pounds
- Uterus: 2.5 pounds
- Stored fat and protein, water retention, and blood volume: 8 pounds
Most women lose much of this extra weight during the birth process and in the first several weeks after birth, especially if they are breastfeeding, which burns an impressive amount of calories. Breastfeeding expends 600 to 800 calories each day. Your body needs the additional calories to synthesize lactose, protein and fat into milk and to ensure the milk is nutritious. Severely undernourished women produce less milk; however, obese women produce the same amount of milk as those of average weight. The amount of vitamins in breast milk, particularly water-soluble vitamins such as C and the B complex, is closely related to how much is consumed in the mother's diet. However, the concentrations of trace elements such as copper fluoride and fat-soluble vitamins seem to be less dependent on the fluctuations in maternal eating habits.
Protein
Protein is necessary to produce new blood cells and circulating proteins for your increased blood volume, and for the physical growth and cellular development of your baby. It is also needed to create the placenta, amniotic tissues, and maternal tissues. Pregnant women need approximately 60 grams of protein a day, or 10 grams more than non-pregnant women. This requirement can be met by eating two large eggs and 2 ounces of cheese, or a 4-ounce serving of meat. Protein is also used to produce breast milk and nourish the baby, so lactation will increase your daily requirements of protein by up to 20 grams (compared to non-lactating and non-pregnant women).
Sodium
Your sodium requirements increase during pregnancy; however, the sodium provided by the average diet is probably adequate for expectant mothers and consumption of additional salt is rarely warranted. Americans typically consume 4,000 to 8,000 mg of sodium each day, well above their daily needs of 2,400 mg. Excessive sodium intake does contribute to high blood pressure in some people, so women who have been advised to limit sodium before becoming pregnant should continue this practice until they discuss it with their doctors.
Sugar
Experts at the American Diabetes Association believe that hormones secreted during pregnancy may make it hard for your body to use insulin (a condition called insulin resistance), which allows more glucose to stay in your bloodstream. When glucose remains in the bloodstream instead of being converted to energy, it can lead to a condition called gestational diabetes which affects approximately 2 to 5 percent of pregnant women. Women with gestational diabetes should be closely monitored to make sure their blood sugar levels remain steady. If blood sugar rises too high, the increased sugar crossing the placenta can result in an abnormally large fetus, which can complicate labor and delivery and cause additional problems for the baby after birth.
Nausea
Nutrition and eating habits can even relieve some women's nausea during early pregnancy. To help alleviate morning sickness, try the following:
- Keep meals small, and avoid long periods without food.
- Drink fluids between, but not with, meals.
- Avoid foods that are greasy, fried or highly spiced.
Improvements in the ability to diagnose birth defects early in pregnancy have focused attention on ways to correct certain fetal defects by manipulating the mother's diet. For example, researchers are investigating the use of vitamin and mineral supplements to prevent neural tube defects. Other research is being conducted on the ways maternal nutrition can help fetuses with inherited birth defects, usually inborn errors of metabolism, in which certain nutrients are not processed normally.
Scientists are also analyzing the extent to which pregnancy affects a woman long-term. Jean Pennington, Ph.D. of the United States Department of Health and Human Services, says it is known that a woman who has a large number of children may have depleted calcium stores. Walter H. Glinsmann, M.D., Past Associate Director for Clinical Nutrition, FDA Center for Food Safety and Applied Nutrition, counsels that having babies should be considered a major life effort that begins long before conception, "Getting pregnant is like running a race. You have to get yourself in condition."
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