Nutritional Counseling for Vegetarians During Pregnancy and Lactation

Debra S. Penney, CNM, MS, MPH; Kathleen G. Miller, CNM, MS

Disclosures

J Midwifery Womens Health. 2008;53(1):37-44. 

In This Article

Vegetarian Nutrition During Pregnancy and Lactation

Few studies have specifically addressed vegetarian nutrition and pregnancy outcomes. Some studies have suggested benefits such as a low rate of preeclampsia among vegans[13] and reduction in preterm birth among pregnant women on a low cholesterol diet.[14] Yet recommended dietary guidelines for vegetarians during pregnancy and lactation are lacking.

General food group recommendations have been made for vegetarians in pregnancy. The Physicians Committee for Responsible Medicine[7] suggests that vegetarian pregnant women consume daily portions of dark green vegetables (1-2 servings), other vegetables and fruits (4-5 servings), bean and soy products (3-4 servings), whole grains (6 or more servings) and nuts, seeds, and wheat germ (1-2 servings). With the exception of folic acid, recommendations in the US Dietary Guidelines[9] are not specific to pregnancy. These guidelines also emphasize that women of childbearing age who could become pregnant should consume adequate synthetic folic acid daily in addition to food forms of folate from a varied diet. A healthy daily diet is outlined for adults and includes 2 1/2 cups of fruits and vegetables from a variety of sources, 3 or more ounce-equivalents of whole grains, and 3 cups of low fat milk products. Vegetarian choices are outlined and should include sources of protein, iron, and vitamin B-12 intake, as well as calcium and vitamin D if avoiding milk products. Charts listed in these guidelines are helpful for substituting beans, tofu, nuts, and seeds for meats, and include alternative food sources for calcium if avoiding milk and dairy products ( Table 1 ).

In 1997, nutrient requirements were defined by the Food and Nutrition Board of the National Academy of Sciences as dietary reference intakes (DRIs). There are four types of DRI reference values: the estimated average requirement (EAR), the recommended dietary allowance (RDA), the adequate intake (AI) and the tolerable upper intake levels (UL) ( Table 2 ).[15] The EAR is the average daily nutrient intake level estimated to meet the requirement of half the healthy individuals in a particular age or gender group.[9] The RDA is the estimated level of dietary intake sufficient to meet the needs of nearly all of the healthy individuals in a particular group.[9] AI is a recommended intake value based on observed or experimentally determined estimates, assumed to be adequate, of a nutrient intake by a group of healthy people. It is used when the RDA cannot be determined.[15] The UL is the highest level of daily nutrient intake that should pose no risk of adverse effects for almost all individuals in the general population.[15] Not all nutrients have an established DRI. RDAs and AIs may both be used as goals for individual intake.[9] Values for selected nutrient intake during pregnancy and lactation are discussed below.

Vegetarian diets vary between individuals; therefore, it is important that health care providers assess dietary intake with each individual. Without good information and planning, vegetarians may be at risk for some deficiencies. Several studies have shown that vegetarian diets may be low in vitamin B-12, vitamin D, calcium, protein, and iodine.[6] Thus, dietary assessment of a pregnant or lactating vegetarian should take into consideration both the potential nutrient inadequacies unique to vegetarians and those nutrients important for pregnancy and lactation. A 3- to 7-day diet history is a good place to start, and can be repeated as needed throughout pregnancy and lactation. Assessment of the following nutrients is suggested: vitamin B-12, vitamin D, calcium, iron, essential fatty acids, and protein. Total caloric intake to meet the energy needs of pregnancy and lactation are also important to assess. Weight gain and energy requirements are the same as for other pregnant women.

Vitamin B-12 (cobalamin) functions as a methyl donor and works with folic acid in the synthesis of DNA and red blood cells.[16] It is important in maintaining the myelin sheath of nerve cells.[16] A deficiency may not be manifested for several years, because this vitamin is stored in the liver and kidney.[16] In its natural state, vitamin B-12 is found only in animal sources of food. Tuna, beef, and milk products are good sources of vitamin B-12.[17]

There has been little research on vitamin B-12 in pregnancy, and much is yet unknown. There is evidence of increased intestinal absorption of vitamin B-12 during pregnancy, and fetal needs are thought to be very low.[18] There is speculation that vitamin B-12 from maternal tissue stores do not cross the placenta, but newly absorbed vitamin B-12 is available for transport.[18,19] Vitamin B-12 is absorbed most effectively in small amounts at frequent intervals. Eating foods fortified with vitamin B-12 is a possible way of achieving this.[6]

A low maternal serum level of vitamin B-12 during the first trimester of pregnancy is an independent risk factor for neural tube defects.[18] In addition, low serum vitamin B-12 concentrations are associated with maternal effects that include macrocytic anemia, neurologic complications, and cognitive disabilities.[18] Breast-fed infants of women lacking vitamin B-12 are at risk for developmental abnormalities, growth failure, and anemia.[18]

A high intake of plant-based foods, as is typical of a vegetarian diet, results in a high folate level, which can mask a vitamin B-12 deficiency by correcting the hematologic alterations that are seen with vitamin B-12 deficiencies.[20] In both folate and vitamin B-12 deficiencies, the patient presents with a severe macrocytic anemia (MCV > 100 fL), a low to low-normal absolute reticulocyte count, and a characteristic blood smear showing macroovalocytes, occasional megaloblasts, and hypersegmented neutrophils.[21] To distinguish between the two possible deficiencies, further testing is needed. Serum cobalamin, red blood cell (or serum) folate concentrations, and specific vitamin B-12 metabolites (e.g., methylmalonate and homocysteine) are evaluated to distinguish between the deficiencies.[21] Many persons with B-12 deficiency present without anemia or only mild anemia. The macrocytosis may be masked by a concurrent disorder, such as iron deficiency or one of the thalassemias.[21] In Tina's case above, only mild anemia was present, and no further testing was conducted.

Clinicians should monitor adequate vitamin B-12 intake in those who restrict or abstain from eating animal products, because of the adverse physiologic consequences associated with vitamin B-12 deficiencies. The EAR for daily intake is 2.2 mcg/day during pregnancy and 2.4 mcg/day during lactation.[22] Koebnick et al[18] compared serum vitamin B-12 and homocysteine concentrations in pregnant women consuming either a lacto-ovo vegetarian diet, a low meat diet (<300 g/wk), or a diet with larger amounts of meat (>300 g/wk). Dietary vitamin B-12 intake, serum vitamin B-12, and plasma total homocysteine concentrations were measured once in each trimester. Serum vitamin B-12 concentrations in both low meat eaters and lacto-ovo vegetarians were lower than those eating a meaty Western diet. Vitamin B-12 deficiency was found in pregnant women consuming lacto-ovo vegetarian diets. Based on this finding, the authors recommended a higher intake of vitamin B-12 of more than 3.0 mcg/daily for pregnant women consuming a lacto-ovo vegetarian diet. Neonatal outcomes were not measured in this study.

Low maternal vitamin B-12 intake in pregnancy leads to a low infant status at birth,[23,24] and poor maternal intake during lactation can lead to low vitamin B-12 content in breast milk.[24] The long-term neurological outcome is poor in infants with low vitamin B-12 levels.[24]

A vitamin B-12 supplement is recommended for both lacto-ovo vegetarian and vegan mothers. Foods fortified with vitamin B-12 include meat substitute products, soymilks, tofu, cereals, and nutritional yeast.[25] Seaweed and tempeh are generally not reliable sources of vitamin B-12.[6] Four servings daily of vitamin B-12 fortified foods are recommended in pregnancy and lactation.[25]

There are many forms of vitamin D. Vitamin D-3 enables the utilization of calcium, and both of these nutrients are critical for the development of bones and teeth.[26] All forms of vitamin D cross the placenta to the fetus.[26] Plasma levels of vitamin D depend on sunlight exposure and intake of foods high in vitamin D, fortified foods, or supplements.

Vitamin D deficiency during pregnancy is associated with several disorders of calcium in both the mother and infant, including neonatal hypocalcemia and tetany, infant hypoplasia of tooth enamel, and maternal osteomalacia.[26] Vitamin D deficiencies exist among the general population as well as among some vegetarians. Data from the third National Health and Nutrition Examination Survey indicate that about 42% of African American women and 4% of white women have evidence of vitamin D insufficiency.[27]

Low vitamin D levels have been observed in some vegan populations at northern latitudes.[6,26,28] Vegans have been found to have lower average intakes of vitamin D than lacto-vegetarians and omnivores.[28]

The sources of vitamin D-3 are primarily animal products and skin exposure to natural light.[26] Light-skinned people can obtain sufficient exposure to sunlight on the face, hands, and forearms for 5 to 15 minutes a day during the summer months at the 42nd latitude, but dark-skinned people require longer exposure to obtain sufficient amounts.[6] Sun exposure may be inadequate for those living in northern latitudes or in smoggy regions.[6]

Women who have regular sunlight exposure do not need any extra vitamin D. However, in the absence of adequate exposure to sunlight, 5 mcg/day or 200 IU in the form of cholecalciferol is recommended.[22] There is no increased requirement for vitamin D during pregnancy and lactation.

Vegans must rely heavily on ultraviolet B rays -- the band of ultraviolet which causes synthesis of vitamin D-3 -- from direct sunlight to obtain sufficient D-3.[29] Good sources of vitamin D are found in fish liver oils, fatty fish, and egg yolks, but vitamin content in these foods varies by the time of year.[17] Vitamin D-fortified foods include cow's milk, some soy milk products, and some breakfast cereals.[25] Vegetarians may also choose vitamin D supplements.

Adequate dietary calcium is necessary for maximizing peak bone mass during the first 3 decades of life and for minimizing bone loss.[30] Although many nutrients are important to bone health, calcium is the nutrient that is most likely to be deficient in average diets of women in the United States.[30] Calcium bioavailability from plant foods can be affected by oxalates and phytates, which are inhibitors of calcium absorption.[30] Calcium absorption is inversely proportional to the oxalic acid content in the food.[30] As a result, foods such as spinach and rhubarb have a low calcium bioavailability, whereas kale, broccoli, and bok choi have high bioavailability.[30] Soybeans have a relatively high calcium bioavailability. High plasma levels of protein, caffeine, and sodium can increase urinary calcium excretion.[28] Vegans tend to have lower calcium intake compared to lacto-ovo vegetarians and omnivores, and may need to enhance their dietary intake of calcium through fortified foods and supplementation.[6,28] Pregnant women who ingest sufficient calcium during the second and third trimesters of pregnancy have a higher bone mineral density, as do their children.[31]

During pregnancy and lactation, adequate calcium intake (AI) is considered to be 1000 mg/day, and for younger mothers (between the ages of 14 and 18 years) approximately 1300 mg/day.[32] Because of possible decreased intake and absorption in a plant-based diet, vegetarians and vegans should consume 1200 to 1500 mg/day of calcium, which is about 20% more calcium than that recommended for omnivores.[17] Ideally, their food choices should include low-oxalate (high bioavailability) foods such as bok choi, broccoli, Chinese cabbage, collards, kale, okra, turnip greens, and soy products. Other choices with slightly less calcium bioavailability are fortified soymilk, sesame seeds, almonds, and red and white beans.[6] Pregnant and lactating women should consume a minimum of 8 servings of calcium-rich foods, which can also fit into other food categories, such as vegetables.[25]

The main function of iron is in the formation of hemoglobin. Mild anemia can be considered a physiologic state of pregnancy secondary to the normal hemodilution that occurs during pregnancy.

Studies have indicated that women with very low hemoglobin in the first trimester of pregnancy (<8 g/dL) have an increased risk for preterm birth and fetal growth restriction.[32] During the second and third trimesters of pregnancy, an increase in maternal blood volume and transfer of iron to the placenta and fetus constitute an increased need for iron. Iron absorption from plant (non-heme) and animal (heme) sources is enhanced during pregnancy and increases with each trimester.[32] The prevalence of iron deficiency is not necessarily higher among vegetarians compared with omnivores.[28]

The amount of dietary iron needed in pregnancy is dependent on maternal preconception stores, and is estimated to be 3.5 mg/day during the second and third trimesters.[33] Iron stores in healthy nonpregnant women total approximately 2600 mg, and approximately 1700 mg is used to make hemoglobin. The remainder is stored as ferritin, found in the plasma and bone marrow and hemosiderin in the reticuloendothelial cells of the liver, spleen, and bone marrow.[33]

Population norms for laboratory indices in pregnancy have not been established.[33] Although blood indices and pregnancy outcomes are not well defined for mild anemia, severe anemia (hemoglobin concentrations <6 g/dL) put both mother and baby at risk for adverse health outcomes.[22] Iron depletion that is sufficient to impair red cell production is diagnosed when laboratory values reveal a low serum iron and ferritin, elevated total iron-binding capacity; these are often accompanied by a slightly decreased mean corpuscular volume.[33] Hematocrit and hemoglobin are imperfect measures of anemia, but these indices remain the most common tests for anemia worldwide because they are inexpensive and easy to measure.

The estimated average requirement of iron in pregnancy is 22/mg a day, and 6.5 mg/day during lactation. For pregnant teens, the estimated average requirement of iron is 23 mg/day and 7 mg/day during lactation.[32] Studies have shown that this requirement may actually be lower because of the body's ability to absorb higher amounts of iron each trimester of pregnancy, leading these authors to suggest that a diet containing 10 mg/day of iron would be sufficient.[33] The recommended intake of iron for lactating women is based on iron losses during pregnancy and childbirth, the return of menses at 6 months postpartum, and iron secretion in breast milk.[26]

Plant sources of iron have decreased bioavailability compared to animal sources, and are more sensitive to interactions with other nutrients that can facilitate or inhibit absorption. Inhibitors of iron absorption include calcium, coffee, and fiber.[6] Vitamin C can help enhance absorption by reducing the inhibitory effects of phytate.[6] Both pregnant and lactating women are encouraged to eat plant-based foods high in iron, such as soy products, tofu, beans, lentils, spinach, molasses, whole wheat breads, peas, dried apricots, prunes, and raisins.[34] Iron deficiency anemia is improved by iron supplements.[6] However, there is ambiguity about the diagnostic criteria for anemia during pregnancy and no clear benefit in neonatal or maternal outcome from iron supplementation in healthy pregnant women.[6] In Tina's case, assessing her serum ferritin level might have helped assess her iron status during pregnancy and lactation.

Unsaturated fatty acids are essential for cell membrane function, development and functioning of the brain and nervous system, and the production of eicosanoids (thromboxanes, leukotrienes, prostaglandins, and prostacyclins).[35] Two polyunsaturated fatty acids which are derived from food sources are linoleic acid (n-6) and alpha-linolenic acid (n-3). Once ingested, these essential fatty acids are converted to long-chain polyunsaturated fatty acids within the body by enzyme-mediated elongation and desaturation. Linoleic acid (n-6) is converted to arachidonic acid (AA), and alpha-linolenic acid (n-3) is less efficiently converted to eicosapentaenoic acid (EPA) and DHA.[35,36] DHA is an important component of neural and retinal membranes, and it accumulates rapidly in the brain and retina during the later part of gestation and early postnatal life.[36] A developing fetus obtains long-chain polyunsaturated fatty acids via selective uptake from the mother's plasma. These undergo further chain elongation and desaturation in fetal tissues, including the brain.[35] Adequate provision of DHA is thought to be essential for optimal visual and neurologic development during early life. Maternal DHA supplementation may also affect infant visual function and neurodevelopment during pregnancy and lactation.[36] Studies suggest that fatty acids may influence pregnancy and fetal outcomes, including length of gestation, size of infant, preeclampsia, depression, and infant visual function and neurodevelopment; however, no clear consensus exists.[36]

Both alpha-linolenic acid (n-3) and linoleic acid (n-6) compete for the enzymes responsible for the conversion process.[35] High intake of linoleic acid (n-6) inhibits the synthesis of DHA from alpha-linolenic acid (n-3).[35] Therefore, a balanced intake of n-3 and n-6 fatty acids is important in order to produce sufficient amounts of DHA and EPA. Vegans and vegetarians can be at a disadvantage in balancing this ratio, because they may limit sources of alpha-linolenic acid (n-3) or DHA in their diet, and they typically consume an abundance of linoleic acid (n-6).[37]

More research is needed to understand the quantity of intake and the effect of fatty acids, and in DHA and EPA in particular. These two long-chain fatty acids have important effects on eicosanoid metabolism, membrane properties, and gene expression.[38] The biological activities of n-3 fatty acids have led some to believe that maternal levels of n-3 fatty acids may significantly affect pregnancy outcomes and fetal development. A recent workshop reported that a DHA to AA ratio of 1.4:1 to 2:1 was beneficial for the visual and cognitive development of low-birth weight infants and normal-birth-weight infants.[38]

Levels of EPA and DHA are related to consumption of n-3 fatty acids through foods such as fish, organ meats, eggs, flaxseed, and canola and soybean oils; intake of n-3 fatty acids and resulting levels of EPA and DHA have been found to be negligible in vegans and some vegetarians.[35] In contrast, n-6 fatty acids levels are found to be similar in vegetarian diets compared to omnivores.[35] Most diets are unlikely to be deficient in linoleic acid, because it is derived from plant sources such as nuts, seeds, leafy vegetables, grains, and vegetable oils (corn, safflower, sesame, and sunflower).[37]

Having a balanced ratio between alpha-linolenic acid (n-3) and linoleic acid (n-6) may favor the synthesis of DHA. Several recommendations have been made for a balanced ratio for the general vegetarian population. The National Institutes of Health have suggested a ratio of 2:1 to 3:1 based on AI levels.[39] Lower proportions of DHA have been found in the fetal plasma of vegetarian mothers as compared to mothers who are omnivores.[37] The breast milk of vegetarians and especially vegans in the United Kingdom showed lower DHA levels than omnivores,[6] but in the United States, vegetarians do not have lower levels of DHA in breast milk lipids, probably because of higher intakes of alpha-linolenic acid from soybean oil or preformed DHA.[37] Compared to nonvegetarians, the breast milk of vegetarians was found to have more than twice the linoleic acid and alpha-linolenic acid, but less than half of the DHA.[37] The concentration of DHA in human milk increases with DHA supplementation. Supplementation with DHA during lactation is more effective in raising DHA content in breast milk than supplementing only during pregnancy.[40]

There is no clear consensus on specific recommendations for alpha-linolenic acid (n-3) intake during pregnancy and lactation. Some expert panels have suggested a DHA intake of 300 mg/day during pregnancy and lactation, while others have recommended 200 to 300 mg/day.[36] The position of the American Dietetic Association is to supplement during pregnancy and lactation with DHA or its precursor linolenic acid; this recommendation stems from the importance of DHA and the fact that lower levels are found in the breast milk of vegetarians and vegans.[6] The Institute of Medicine has defined AIs (either by supplement or food sources) to be 1.4 g/day during pregnancy and 1.3 g/day during lactation.[40] Direct sources (i.e., ones that are not converted from n-3 fatty acids) of DHA are found in microalgae in the form of supplements, and in some prenatal vitamins.[6] Plant sources of alpha-linolenic acid (n-3) are ground flaxseed, walnuts, soybeans, and mungo beans. Natural oil sources include flaxseed, linseed, and canola. One teaspoonful of flaxseed oil or a tablespoon of ground flaxseed will supply the daily requirement of alpha-linolenic acid. Heat damages this oil, so it should not be used in cooking.[35]

Protein requirements during pregnancy and lactation are increased to 71 g/day compared to 46 g/day for the nonpregnant woman.[41] Additional protein is needed in pregnancy to allow for the estimated 21 g/day deposited in fetal, placental, and maternal tissues during the second and third trimesters. Proteins from plant sources are sufficient to meet these needs. Complementary proteins containing all of the essential amino acids do not need to be consumed at the same meal, but can instead be eaten over the course of the day.[6] Sources of protein include legumes, nuts, tofu, and eggs. Isolated soy protein can meet protein needs as effectively as animal protein.[25]

Although some vegan women have protein intakes that are marginal, typical protein intakes of lacto-ovo vegetarians and some vegans meet or exceed the requirements.[6] The quality of proteins from plants vary. Protein quality is determined by the protein digestibility corrected amino acid score.[6] Wheat protein eaten alone may be 50% less useable than animal protein, whereas isolated soy protein can meet protein needs as effectively as animal protein.[6] Therefore, protein needs might be higher than the RDA in vegetarians whose dietary protein sources are mainly those that are less well digested like cereals and legumes.[6] Cereals tend to be low in lysine; this essential amino acid can be obtained by using more beans and soy products. An increase in all sources of protein can compensate for a low lysine intake.[6] Providing the client with a chart that lists the essential amino acid contents in plant sources may be helpful.

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