Diet Composition

The amount of energy contributed by the macronutrients—carbohydrate, protein, and fat—does not vary substantially during normal pregnancy. The role of each of these nutrients in normal physiology and metabolism remains intact with a heightened importance for some functions in the context of fetal growth and development. For that reason, it is critical that pregnant women do not self-impose diet restrictions or extremes during pregnancy.

13.3.2.1 Carbohydrate

Carbohydrate is the brain's main fuel and the nutrient that fuels muscles for daily tasks and exercise. The growing fetus relies on the mother's carbohydrate supply. A diet too low in carbohydrate can affect the energy level of the mother. During normal pregnancy, care should be taken to ensure that 50-60% of daily calories are provided as carbohydrate. Diets low in carbohydrate should not be attempted during pregnancy, as the effects of such a diet on fetal development are not known. Carbohydrate source should be well planned to ensure that the majority of carbohydrates are complex, with a limited consumption of refined sugar or simple carbohydrate. Examples of complex carbohydrates include bread, rice, beans, pasta, and potatoes. When grains are refined, they are stripped of many important nutrients, including fiber, which are important in pregnancy. Pregnant women should be advised to consume whole-grain bread, cereal, and pasta products. Fruits, vegetables, and whole-grain products are good sources of dietary fiber that are beneficial in preventing constipation during pregnancy. Foods with simple sugar like candy, soft drinks, and desserts should be limited during pregnancy as they are high in calories and low in nutritional value. These fat and sugar-laden foods can displace other more nutritious foods and contribute to accelerated weight gain. A woman requiring 2,500 kcal daily would need 275-330 g of carbohydrate daily. One slice of bread, 1/2 cup of cooked pasta, 1/2 cup dry cereal or a serving of fruit all provide ~15 g of carbohydrate per serving.

13.3.2.2 Protein

Adequate protein intake during pregnancy is important to maintain maternal health during pregnancy as well as provide important building blocks for fetal growth and development. Protein provides the structural framework for the body, is integral to the immune system, transports substances throughout the body, is the basis for many hormones and enzymes, and maintains fluid balance. Pregnant women need a minimum of 60 g of protein daily [2]. Good sources of dietary protein include meat, poultry, fish, dairy products, legumes, beans, and nuts. One ounce of meat, poultry, fish, or cheese provides 7 g of protein. One 8-oz. glass of skim milk provides 9 g of protein. Two 3-oz. servings of meat, poultry, or fish and three 8-oz glasses of milk will provide the protein necessary to meet the protein needs of pregnancy.

Fat is more energy dense than carbohydrate or protein (9 kcal/g vs. 4 kcal/g for fat and carbohydrate and protein, respectively) when consumed within recommended guidelines, fat is beneficial to maternal health and fetal development. Fats are important in maintaining skin health, as a structural component of cells, for absorption of vitamins A, D, E, and K as regulatory messengers (hormones), hormone, and for immune function. Recent evidence suggests that omega-3 fatty acids consumed during pregnancy are beneficial to cognitive development in infancy and childhood [11-14]. Pregnant women should consume 25-30% of their daily energy as fatty acids. A woman requiring 2,500 kcal/day would need to consume 69-83 total grams of fats daily. These fat requirements should be met using vegetable-based oils made up of unsaturated fat rather than animal and plant-based saturated fats that can be more problematic to health [15].

Sources of unsaturated fats include olive oil, canola oil, peanut oil, sunflower oil, flax seed oil, and fish oil. Canola oil and flax seed oil are sources of the essential fatty acid a-linolenic acid. Dietary oils either derived or obtained directly from fish are particularly beneficial during pregnancy as fish contains a preformed source of docosahexaenoic acid (DHA) which is the metabolic end product of a-linolenic acid in the body [16] and preferentially transferred to fetal tissue during pregnancy [17-19]. Women should consume 300 mg of DHA daily during pregnancy [20]. Many pregnant women are concerned about eating fish during pregnancy due to potential contamination; however, women need to be educated about safe fish intake during pregnancy to ensure consumption of these important omega-3 fatty acids (http://www.cfsan.fda.gov/~comm/haccp4.html). Omega-6 fatty (linoleic) acid should make up 2% of total energy during pregnancy. This recommendation does not differ from the recommendation for the general adult population [20].

Table 13.3

Micronutrient Deficiency Risks Associated with Various Popular Diets

Popular diet type:

Micronutrient

Fat restrictive Protein restrictive Non-dairy

Carbohydrate restrictive

Fat soluble vitamins (A, D, E, K), essential fatty acids Iron, vitamin B12, zinc, magnesium, essential amino acids Calcium, vitamin D

B vitamins, vitamins C, A, K and D, potassium, fiber

Sources of saturated fat include whole milk, beef, cheese, lard, shortening, and palm and coconut oil. No more than 10% of daily calories should come from a saturated fat source. A woman who requires 2,200 kcal daily should consume no more than 24 g of saturated fat daily.

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