Protein is one of the few nutritional components known to be increased during pregnancy. Fortunately, this additional requirement can be easily met through food, which is advised over supplements such as drinks, powders, bars, or shakes.
Vegans and vegetarians can also meet this increased need as long as their plant sources are varied, as most single plant sources do not contain all essential amino acids needed during pregnancy.
Unless otherwise directed by a health care provider (HCP), high protein (and/or carbohydrate restriction) diets are not advised and may be harmful during pregnancy.
Women who are concerned about their protein intake during pregnancy, or have questions regarding the overall nutrition of their diet, should speak to their HCP.
Background
Protein is the second most abundant compound in the body (after water), most of which is muscle, followed by skin and blood. Protein is also found in bone, body fluids, hair, internal organs, and nearly every other part of the body.
Proteins, along with amino acids, are “the building blocks of life". Protein influences many chemical reactions necessary for functioning, healing, repair, immune response, blood clotting, fluid balance, vision, production of hormones, energy, and carrying oxygen in the blood.
Plant and animal proteins are composed of more than 20 individual amino acids, which result when proteins are broken down and digested.
The body uses amino acids for growth, development, digestion, synthesis of hormones and neurotransmitters, and body tissue repair, as well as many other bodily functions.
Protein from animal sources contain the full range of essential amino acids needed by the body that must be obtained through food.
Vegans and vegetarians can get all amino acids necessary by combining different plant sources of protein and cereals (single sources of plant foods do not contain all essential amino acids).
In addition to amino acids, foods rich in protein are also important sources of riboflavin, vitamin B6, vitamin B12, choline, copper, iron, phosphorus, selenium, vitamin D, vitamin E, and zinc.
Pregnancy
Pregnancy is a stage of rapid growth and development, and enough dietary protein is critical for optimal health of both mother and baby. Amino acids are continuously and actively transported across the placenta to the fetus. For most amino acids, the plasma concentrations in the fetus are higher than in the mother.
Certain amino acids are thought to be absolutely essential during pregnancy because the amount needed for adequate growth (and storage of protein) is high, and the pathways to do this in the fetus are not fully developed. Therefore the fetus requires amino acids from the mother.
Adjustments in protein metabolism occur within several weeks of conception. Although the fetus may need minimal protein in early pregnancy, the mother needs it right away due to significant blood volume expansion and tissue growth.
From then on, protein requirements for both mother and fetus increase, with the highest requirement during the third trimester.
Requirements
There are many differing opinions regarding protein requirements for non-pregnant adults, let alone pregnancy.
In the United States, the recommended daily allowance of protein for all adults is 0.75 g of protein per kilogram (1 kilogram = 2.2 lbs) of body weight per day.
The U.S. National Academy of Medicine recommends anywhere from 10% to 35% of calories from protein each day.
It has been estimated that pregnant women need approximately 1.2 and 1.52 g of protein per kilogram of body weight each day, during early and late pregnancy, respectively. (Note: A 150-pound woman would require approximately 82 to 103 g/day, adjusted occasionally due to an increase in body weight as pregnancy progresses).
Other estimates are lower than this amount. Without taking the mother’s weight into consideration, it has been recommended that women aim for approximately 60 g/day of protein throughout pregnancy, and that this can be met through simple dietary changes.
Dietary surveys indicate women may already achieve this amount. Common protein intake by pregnant women in the United States ranges from 75 to 110 g/day, and 64 g/day for women in the United Kingdom.
Deficiency/Lack of Protein
In general, protein deficiency can cause growth failure, loss of muscle mass, decreased immunity, and weakening of the heart and respiratory system.
Protein restriction may even affect fertility. An animal study published in June 2021 indicated that protein restriction prior to and during pregnancy negatively affects follicle quality by reducing size and activation capacity (ability to generate mature eggs).
A lack of protein during pregnancy results in consistently decreased fetal growth, and the developing fetus may not adequately compensate for these negative effects.
An animal study published in February 2021 indicated that a maternal low-protein diet could potentially harm fetal kidney development.
Therefore, unless strictly recommended by an HCP, protein restriction during pregnancy is not recommended.
Excess Protein
Higher protein intakes during pregnancy have been debated for decades.
High amounts of excess protein – such as restriction of carbohydrates resulting in a significant intake of protein (the keto diet, Atkins) – have been shown to be harmful during pregnancy.
Numerous studies have shown that high protein consumption (more than 35% of calories, or 40 g daily + normal intake) during pregnancy was associated with higher preterm birth rates, lower birth weights, increased risk of infants born small-for-gestational age (different from birth weight), and a higher number of neonatal deaths.
Higher protein intake might cause competition among amino acids, which could negatively affect fetal growth.
Additional studies illustrate that a strict, high protein-low-carbohydrate diet (when not specifically advised by an HCP) could cause intrauterine growth restriction and organ growth changes in the fetus. The mother could experience high cortisol (stress hormone) levels, a higher risk of hypertension and diabetes, and potential kidney problems.
Further, it has been recommended that the use of special protein powders or specially formulated high-protein beverages should be discouraged.
Ketosis results when carbohydrate intake is restricted and the body turns to other energy sources, such as fat; ketone bodies are then released into the blood.
Ketone bodies freely pass through the placenta; a by-product of ketone bodies have been detected in rat fetal plasma after five-minutes of injecting the by-product into the mother’s blood.
Ketone bodies can affect fetal growth and organ development, especially the central nervous system, although this is not completely understood.
The Keto Diet specifically, can also cause difficult short-term side effects (when first started) that could be exacerbated during pregnancy, such as nausea, vomiting, leg cramps, loss of electrolytes, headache, fatigue, dizziness, insomnia, difficulty tolerating exercise, and constipation.
Any form of protein supplementation or significant purposeful dietary intake appears to only be beneficial in women who are lacking protein in their daily diet. In this situation, additional protein can help prevent intrauterine growth restriction and low-birth weight.
Food Sources
Foods that contain protein are generally also good sources of vitamins and minerals. These foods include grains, fruits, milk, cheese, and dried peas, beans, and other vegetables.
Plant-based protein sources may lack one or more essential amino acids. Therefore, a diet based on a single plant item is not enough, and it is necessary for women to eat a variety of plant sources throughout the day, especially those who do not consume meat or dairy.
Action
Women who are concerned about their protein intake during pregnancy, or have questions regarding the overall nutrition of their diet, should speak to their HCP.
Carbohydrates are healthy and necessary during pregnancy, and there is no need to restrict their intake, unless specifically advised by an HCP (i.e. gestational diabetes). Women should read more about carbohydrate intake during pregnancy and how the fetus requires them for growth and development.
Resources
Protein (Harvard University, T. H. Chan School of Public Health)
All About Proteins (ChooseMyPlate.gov)