Stephens TV, Payne M, Ball RO, Pencharz PB, Elango R. Protein requirements of healthy pregnant women during early and late gestation are higher than current recommendations. J Nutr. 2015;145(1):73-78.
Twenty-nine healthy women with no complications of pregnancy, aged 24 to 37 years: 10 participated only during early gestation, 12 only during late gestation, and 7 during both. Subjects chose to complete between 1 and 4 study days during each study period. If subjects chose more than 1 day per period, test days were separated by at least 5 days.
Study Parameters Assessed
This study used the Indicator Amino Acid Oxidation (IAAO) technique to assess protein requirements for these women. IAAO technique is predicated on the assumption that if any amino acids are deficient for protein synthesis, any extra remaining amino acids will be oxidized. As additional amounts of the deficient amino acids are given, oxidation will decrease. As protein needs are met by the body, the rate of oxidation will stabilize.
In this test, participants were given isocaloric diets (1.7X the calculated resting energy expenditure [REE] of each individual) with variable amounts of protein (3%-21% of total calories or 0.22 g/kg-2.56 g/kg body weight), with the exception of carbon 13‒labeled phenylalanine and tyrosine, which were given in constant doses to measure oxidation levels. Urine and breath samples were taken at baseline and at 2.5 hours after the introduction of the tracer amino acid (6 samples taken every 30 minutes).
Primary Outcome Measures
The rate of phenylalanine tracer oxidation was calculated for each subject to show at which protein dosage oxidation levels had stabilized, indicating that the woman’s protein needs had been met.
IAAO testing indicated that protein needs were met for pregnant women at 1.22 g/kg during early pregnancy and 1.52 g/kg in late pregnancy.
Especially during a first pregnancy, many women have a pronounced concern about diet: how to eat, what to eat, and when to eat. As providers, we have the opportunity to guide them toward optimal nutrition and provide reassurance that they are making sound choices. Within the context of so many “don’ts” regarding maternal nutrition—foods to avoid because of possible bacterial contamination, mercury, lead, pesticides, or nitrates; blood sugar dysregulation; insufficient or too much weight gain—it is good to also have some advice that helps women relax and trust their intuition. This study finds that the protein needs of women throughout pregnancy are higher than previously recommended and possibly closer to what women may be craving.
While it can be confusing to create an optimal diet for each individual during pregnancy, the findings from this study indicate that advising higher protein intake may be in keeping with what is intuitive for the patient.
IAAO is a relatively new method that has become popular for determining protein requirements in human subjects.1-4 In the past, protein requirements were assessed by the nitrogen balance method, which can be difficult to assess because it requires that all nitrogen intake and output be carefully recorded and that the subject stay in the testing facility for the duration of the testing to measure nitrogen loss from urine, feces, saliva, and wounds. This testing takes much longer to perform and requires subjects to be put in a deficiency state for longer, which makes it unsuitable for pregnant women. For this reason, the current recommendations for protein intake during pregnancy (estimated average requirement of .88 g/kg and recommended daily allowance of 1.1 g/kg) have been based on nitrogen balance studies of nonpregnant adults that have been extrapolated with total body potassium studies of protein deposition during pregnancy.5 With the development of IAAO, researchers have been able to more accurately determine protein needs during pregnancy because they can run this test on pregnant women. Additionally, this is one of the first studies to distinguish maternal needs during early and late gestation periods.
Understanding protein requirements during pregnancy is important because protein is the macronutrient that most influences birth weight. This study assumes caloric sufficiency; for well-nourished nondiabetic women, protein is the macronutrient most likely to increase birth weight.6,7 In addition to neonatal complications and increased mortality, low birth weight is also correlated with long-term health problems such as type 2 diabetes, kidney disease, cardiovascular disease, and respiratory problems.8-11 Ensuring that pregnant women have a protein-sufficient diet is therefore crucial for the short-term and long-term health of their children.
It is important to keep in mind, however, that while this study showed protein consumption needs to be higher than current recommendations, it does not need to be extraordinarily high. The average weight of the subjects during early pregnancy was 64.4 kg, indicating a need for 78.6 g protein per day or 314 calories from protein. Calculated REE averaged 1,370 calories per day, so subjects were given an average of 2,329 calories (1.7 REE), putting sufficient protein consumption at 13.5% of calories. In late pregnancy, average weight was 71.1 kg, with a need for 108.1 g protein or 432 calories per day. REE was 1,480, so subjects were given an average of 2,516 calories, with sufficient protein consumption at 15% of calories. That 13% to 15% of calories from protein is far lower than the recommended amounts in virtually any contemporary dietary plan with the exception of some raw, vegan, and Pritikin diets—none of which are recommended during pregnancy.
Based on these new recommendations, the menu example below provides sufficient protein sources on average for late pregnancy with far fewer calories than necessary for a day; a pregnant woman could be encouraged to include these foods within the context of whatever other foods she prefers to meet her additional caloric needs.
- Breakfast: 2 eggs, 2 slices toast=21 g protein
- Snack: 1 oz cheese=7 g
- Lunch: 1 c cooked lentils with steamed veggies=18 g
- Snack: 2 T peanut butter on 2 rye crackers=12 g
- Dinner: 1 c cooked chicken breast with 1 c quinoa and steamed veggies=51 g
- Total: 109 g protein, approximately 1300 calories
With this in mind, practitioners may find that their patients are intuitively be eating an appropriate amount of protein. A current Canadian study found pregnant women generally eating amounts of protein more consistent with the findings of this study, rather than the current daily recommended intake.12 This assumes, of course, that women have adequate caloric intake and the financial and practical means to choose the foods they eat.
One question relevant to how complete the information is from the study is the possible impact of the types of food consumed rather than just macronutrient content. On the day of the study, all of the calories for the day were consumed as a shake consisting of the protein supplement based on an egg-white composition, Kool-Aid or Tang, and a shake base powder consisting of palm, soy, coconut, and sunflower oils; corn syrup; corn starch; sucrose; calcium phosphate; sodium citrate; vitamins; and minerals, plus unspecified “protein-free cookies.” This mixture does meet the requirements of the macronutrient breakdown desired for the purpose of the research study, but it certainly doesn’t resemble a dietary plan that would be advocated by most providers counseling pregnant women. Although this study gives us a good baseline from which to advise patients, it is within the realm of possibility that a pregnant woman’s metabolic and protein needs will shift if fiber, complex carbohydrates, and phytonutrients are present in the diet.
While it can be confusing to create an optimal diet for each individual during pregnancy, the findings from this study indicate that advising higher protein intake may be in keeping with what is intuitive for the patient. Women who are adequately nourished and have the financial means to choose which foods they eat will probably be able to approximately meet their protein needs each day, as long as they feel well enough and remember to eat some protein-containing food every few hours. Women who struggle to meet this recommendation for increased protein intake will need advice from care providers to learn which foods contain protein and to remind themselves to eat these foods every few hours. Doing so will help to optimize the health of the baby as a newborn and throughout life.
- Elango R, Ball RO, Pencharz PB. Indicator amino acid oxidation: concept and application. J Nutr. 2008;138(2):243-246.
- Elango R, Ball RO, Pencharz PB. Recent advances in determining protein and amino acid requirements in humans. Br J Nutr. 2012;108 Suppl 2:S22-S30.
- Elango R, Humayun MA, Ball RO, Pencharz PB. Protein requirement of healthy school-age children determined by the indicator amino acid oxidation method. Am J Clin Nutr. 2011;94(6):1545-1552.
- Elango R, Humayun MA, Ball RO, Pencharz PB. Evidence that protein requirements have been significantly underestimated. Curr Opin Clin Nutr Metab Care. 2010;13(1):52-57.
- Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: National Academies Press; 2002.
- Cucó G, Arija V, Iranzo R, Vilà J, Prieto MT, Fernández-Ballart J. Association of maternal protein intake before conception and throughout pregnancy with birth weight. Acta Obstet Gynecol Scand. 2006;85(4):413-421.
- Imdad A, Bhutta ZA. Effect of balanced protein energy supplementation during pregnancy on birth outcomes. BMC Public Health. 2011;11 Suppl 3:S17.
- Harder T, Rodekamp E, Schellong K , Dudenhausen JW, Plagemann A. Birth weight and subsequent risk of type 2 diabetes: a meta-analysis. Am J Epidemiol. 2007;165(8):849-857.
- Aarnoudse-Moens CS, Weisglas-Kuperus N, van Goudoever JB, Oosterlaan J. Meta-analysis of neurobehavioral outcomes in very preterm and/or very low birth weight children. Pediatrics. 2009;124(2):717-728.
- Yang Z, Huffman SL. Nutrition in pregnancy and early childhood and associations with obesity in developing countries. Matern Child Nutr. 2013;9 Suppl 1:105-119.
- Zohdi V, Sutherland MR, Lim K, Gubhaju L, Zimanyi MA, Black MJ. Low birth weight due to intrauterine growth restriction and/or preterm birth: effects on nephron number and long-term renal health. Int J Nephrol. 2012;2012:136942.
- Stephens TV, Woo H, Innis SM, Elango R. Healthy pregnant women in Canada are consuming more dietary protein at 16- and 36-week gestation than currently recommended by the Dietary Reference Intakes, primarily from dairy food sources. Nutr Res. 2014;34(7):569-576.