Nutrient Needs During Pregnancy - Through the Life Cycle

Nutrient requirements during pregnancy are not static.

They vary during the course of pregnancy depending on prepregnancy nutrient stores, body size and composition, physical activity levels, stage of pregnancy, and health status. For the most part, nutrient needs can be and are optimally met by consuming well balanced, adequate, and healthful diets consisting of basic foods. Healthful diets established during pregnancy can last well beyond preg-nancy and benefit health for life.

Carefully conducted studies of diet and pregnancy outcome in the first half of the twentieth century began the era of scientifically based recommendations on nutri-tion and pregnancy. The now-classic studies conducted by Bertha Burke at Harvard in the 1940s were particularly in-fluential.⁹⁸ These studies showed that diet quality during pregnancy, assessed using diet histories, was strongly re-lated to newborn health status. Newborns assessed as hav-ing optimal physical condition by pediatricians were found to be much more common among women consuming high-quality diets, whereas those with the poorest physical condition were born to women with the poorest-quality diets. Average birth weight of newborns assessed as being in optimal physical condition was 7 pounds, 15 ounces in females, and 8 pounds, 8 ounces in males.⁹⁹ Although Burke’s studies did not show that high-quality pregnancy diets by themselves were responsible for robust newborn health, they provided some of the first evidence that prena-tal diet quality may strongly influence pregnancy outcome.

Thousands of other studies on the effects of nutri-tion on the course and outcome of pregnancy are now available. The following sections highlight research re-sults and recommendations related to calories, key nu-trients, and other substances in food that influence the course and outcome of pregnancy.

The Need for Energy

Energy requirements increase during pregnancy, mainly due to increased maternal body mass and fetal growth.

The additional requirements can be allocated to different

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Artificial Sweeteners There is no evidence that con-sumption of aspartame (Nutrasweet) or acesulfame K (Sunette) is harmful in pregnancy.¹⁰⁵ Diet soft drinks and other artificially sweetened beverages and foods are of-ten poor sources of nutrients, however, and may displace other, more nutrient-dense foods in the diet.

Alcohol and Pregnancy Outcome

Far fewer pregnant women consume alcohol than do non-pregnant women. Approximately 12.2% of pregnant women in the United States consume an alcohol-containing beverage once in a month during pregnancy, whereas about 54% of women who are not pregnant drink that amount.⁶⁰ Most women appear to be aware of the message that not drinking during pregnancy is good for the developing fetus.

Alcohol ingested by a pregnant woman readily passes through the placenta to the fetus where it can interrupt normal growth and development. Adverse effects of high amounts of alcohol intake (such as several drinks per day or more) are strongly related to abnormal mental devel-opment and growth in the offspring, and the deficits are lifelong. Adverse effects of alcohol intake during preg-nancy are mild or undetectable when intakes are low or when alcohol intake exists but is infrequent.

There is no clearly defined safe level of alcohol intake during pregnancy; therefore it is strongly advised that women who are pregnant do not drink. It is further recom-mended that women who may become pregnant not drink alcohol. In utero alcohol exposure during the first, critical months of pregnancy may impair organ development.¹⁰⁶

Frequent consumption of high amounts of alcohol from early pregnancy onward is related to the develop-ment of fetal alcohol syndrome. This topic is addressed in the next chapter.

The Need for Protein

The recommended protein intake for pregnancy is 125 grams per day, or 71 grams daily, and as 1.1 gram/

kg body weight, for females aged 14 and older. On av-erage, pregnant women in the United States consume 78 grams of protein daily.¹⁰² Physiological adaptations in protein metabolism during pregnancy shift in the di-rection of meeting maternal and fetal needs for protein.

Consequently, less protein is used for energy and more is used for protein synthesis.¹⁰⁷

Protein requirements increase during pregnancy pri-marily due to protein tissue accretion. Of the approxi-mately 925 grams of protein (2 pounds) accumulated in protein tissues during pregnancy, 440 grams are taken up by the fetus, 216 grams are used for increases in maternal blood and extracellular fluid volume, 166 grams are con-sumed by the uterus, and 100 grams are accumulated by the placenta. Additional protein is also required to main-tain the protein tissue developed.¹⁰² Protein supplements maintenance organization.¹⁰¹ The graph indicates that

estimated caloric balance is higher than caloric intake throughout pregnancy and becomes negative postpar-tum. The positive caloric balance observed during preg-nancy is due to the fact that women consumed more calories than they expended in physical activity and basal metabolism.

Adequacy of calorie intake is most easily assessed in practice by pregnancy weight gain. Rates of gain in women who do not have noticeable edema are a good indicator of caloric balance.

The Need for Carbohydrates

Approximately 50–60% of total caloric intake during pregnancy should come from carbohydrates. Women should consume a minimum of 175 grams carbohydrates to meet the fetal brain’s need for glucose. On average, women in the United States consume 53% of calories (269 g) from carbohydrates during pregnancy.¹⁰²Basic foods such as vegetables, fruits, and whole-grain prod-ucts containing fiber and a variety of other nutrients are good choices for high-carbohydrate foods. These foods provide beneficial phytochemicals, such as plant antioxidants, and protection against constipation.¹⁰³ In addition, sources of carbohydrates that do not con-tain added sugars and fat tend to be less energy-dense than foods that do and may help women manage preg-nancy weight gain.¹⁰⁴

Illustration 4.14 Estimated caloric balance in pregnancy through 6–8 weeks postpartum.

500

400

300

200

100

Estimated kcal balance

kcal intake

Cumulative Energy Change (Kcal ± SE)

Baseline (0), Pregnancy Quarters, and Postpartum (PP) Time Intervals

0 1 2 3 4 PP

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include legumes (such as lentils, chickpeas, black-eyed peas, black beans, and lima beans) and grains (corn, rice, bulgur, and barley, for example). Protein requirements in vegetarians whose main source of protein is cereals and legumes may be 30% higher than for non-vegetarians due to the low digestibility of protein in these foods.¹¹⁰

Availability of vegetarian food products in large gro-cery and organic-food stores has expanded substantially in the past few years. Vegetarians can now select veggie burgers, meat analog entrees, meals-in-a-cup, and frozen desserts from food-store shelves. Fortified juice, soymilks, breakfast cereal, and meat substitutes are available and can contribute substantially to vegetarians’ intake of vitamins B₁₂ and D and calcium. DHA derived from algae can be used to provide a source of this omega-3 fatty acid do not benefit the course or outcome of pregnancy in

well-nourished women.¹⁰⁸

Protein content of nonvegetarian diets can be simply estimated by evaluating women’s usual daily intake of ma-jor sources of protein. A tool for estimating protein intake is shown in Table 4.20.

Vegetarian Diets in Pregnancy

“The topic of vegetarian dietary practices often brings with it a variety of images and attitudes regarding those who follow such practices. Those attitudes may have limited, if any, basis in actual fact.”

Patricia Johnston, 1988¹⁰⁹

Nutrient needs in pregnancy may be met by many different types of diets, including those that omit animal products.⁹⁷ It is the type and amount of food consumed, not the label placed on it, that determines the appropriateness for dietary intake during pregnancy.

A food guide for pregnant women who exclude ani-mal products from their diet can be found in Table 4.21.

Diets of pregnant vegetarians are sometimes low in vita-mins B₁₂ and D, calcium, iron, zinc, and omega-3 fatty ac-ids eicosapentaenoic and docosahexaenoic acac-ids due to the lack of consumption of rich food sources of these nutrients.

Vitamin B₁₂ deficiency during pregnancy may not become apparent until after delivery. Two cases of neurological im-pairment and growth failure due to maternal B₁₂ deficiency were identified in 4- to 8-month-old infants in Georgia in 2001. Both infants were born to women who followed a vegetarian diet during pregnancy.¹¹³

Protein intake is generally adequate in the vegetarian diet, but it may be low in vegans. Protein needs are met by vegetarians who regularly consume a variety of plant sources of protein and meet energy needs. In pregnant women who consume no animal products, the variety of plant protein sources needs to include complementary sources of protein daily. Protein sources that comple-ment each other, or provide a complete source of protein,

Table 4.20 Tool for estimating protein intake

Food

Protein, Grams

How much protein is there in this usual day’s diet?

Milk, 1 c 8 2 slices toast 6

Cheese, 1 oz 7 1 c milk 8

Egg, 1 7 3 oz tuna 21

Meat, 1 oz 7 2 sl bread 6

Dried beans, 1 c 13 2 oz chicken 14 Bread, 1 slice or oz 3 1 oz cheese 7

2 tortillas 6

1⁄2 c refried beans 7 Total g protein 5 75

Table 4.21 Vegetarian food guide adapted for pregnant women^110–112

Food Group

Servings per Day A. Grains

Whole-grain bread, 1 slice Cooked grains, ¹⁄2 c Fortified cold cereal, 1 oz Fortified cooked cereal, ¹⁄2 c Corn, ¹⁄2 c

Pasta, ¹⁄2 c Tortilla, 1 small Crackers, 4 small

6–11

B. Legumes, Nuts, Seeds, Dairy 5–7 Dried beans, cooked, ¹⁄2 c

Peas, ¹⁄2 c

Soy products, ¹⁄2 c or 2–3 oz Soynuts, ¹⁄4 c

Nut and seed butter, 2 Tbsp Nuts and seeds, ¹⁄4 c Eggs, 1

Cow’s milk, 1 c Cheese, 1 oz Yogurt, ¹⁄2 c

Fortified soymilk, 1 c

C. Vegetables 4

Cooked vegetables, ¹⁄2 c Raw vegetables, 1 c Vegetable juice, ¹⁄2 c

D. Fruits 2

Medium-sized fruit, 1 Cut-up raw or cooked, ¹⁄2 c Fruit juice, ¹⁄2 c

Dried fruit, ¹⁄4 c

E. Fats, Oils, and Sweets 21 depending Mayonaise, oil, margarine, 1 Tbsp

Honey, syrup, jams, jellies, sugar, 1 Tbsp

on caloric need

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Dalam dokumen Through the Life Cycle (Halaman 137-140)