Firstly… Let’s just take a moment to appreciate the female body. Creating another life is no mean feat and it’s not unlike a miracle. The adaptations that take place in the female body to cater for the development of a new life is a fascinating process. To complement our recent post on “Getting fit for two: Working out while pregnant”, here’s a little more insight into the nutritional side of things.
In recent years, research has started to confirm what traditional cultures knew – that the nutritional environment experienced within the womb affects not only our health at birth and early childhood, but it also has an impact on our lifelong risk of chronic lifestyle diseases such as obesity, diabetes, heart disease and more. Researchers have termed this the Developmental Origins of Health and Disease (DOHAD). The DOHAD theory suggests that the nine months of pregnancy is the most important period of our lives and can permanently influence the wiring of our child to be’s brain, along with the functioning of our organs and susceptibility to disease, our metabolism and more.
During pregnancy, significant maternal physiological adjustments occur to ensure the foetus receives the necessary nutrients. We see a change in nutrient metabolism, storage, and tissue fluid concentrations and consequently, indicators of nutritional status need to be interpreted differently in a pregnant woman. In general, the alterations in maternal metabolism result in improved absorption and utilisation of nutrients which means that additional nutrient requirements are in effect less than would be expected.
ENERGY REQUIREMENTS – It’s a lot less than you think!
Changes in basal metabolic rate (BMR) and physical activity influence the energy requirements of pregnant women. By the fourth month of gestation, BMR typically raises and exceeds non-pregnant levels by 15-20% by the end of gestation. The increase in BMR is directly related to the increase in cardiac output as a result of the increase in oxygen demands by the foetus and its’ general support for growth.
One of the most important findings from studies of late is the intra-variability in the energy costs of pregnancy- every woman is different! What can be confirmed however is that increases in energy expenditure and BMR are most pronounced in the second half of pregnancy. To account for this, the 2006 Nutrient Reference Values (NRV) recommend an additional 1,400kJ/day during the second trimester and 1,900kJ/day in the third. You can find this in a piece of fruit and a few nuts.
Pregnancy does not require a marked increase in overall food intake.
WHAT ABOUT PROTEIN?
The need for essential amino acids has not been quantified in pregnancy, albeit the need for nitrogen has and since we get this from our protein intake, we can assume that it wise to ensure we’re getting enough. In the last half pregnancy, maternal and lean tissue synthesis takes place, which requires roughly 148g of nitrogen. This equates to about 0.9 g/day and is taken care of by a reduction in urinary nitrogen excretion during pregnancy… thank you, wonderfully intuitive and capable body!
To cover all bases, the recommended increase in protein intake during pregnancy is 0.2 g/kg/day. The increased requirement for protein is based on estimates of the increase in nitrogen content of the maternal and foetal tissues but may not, in fact, be necessary for women who normally consume liberal amounts of protein in the diet. Studies have shown that in Australia, protein deficiency during pregnancy is unlikely to occur except in association with energy deficiency.
The recommended dietary intakes for most nutrients are increased during pregnancy, albeit this is largely due to the increased energy metabolism. Larger increases of note are applied to iron, vitamin C (for iron absorption) and folate due to their unusually high needs thought to be imposed by the foetus, and/or the increased margin of safety.
Required by the foetus and increased metabolic rate of the mother. The RDI during pregnancy is 2.6 μg (micrograms) per day, which is 0.2 μg/day higher than the recommendation for adult females. This is easily achieved within a diet containing some animal products. It is recommended that pregnant women who consume a vegan diet supplement their diet with B12.
Folate deficiency is common during pregnancy. This is due partly because of the increased turnover of cells and partly due to the increased oestrogen and progesterone levels interfering with normal folate metabolism. Folate plays a major role in cell division in DNA and RNA synthesis.
The RDI is 600 μg dietary folate equivalents per day to cover the increased dietary requirement for folate, however, it is stated that ‘this recommendation does not include consideration of additional needs to prevent neural tube defects (NTD) as the neural tube is formed before most women know they are pregnant’. The Australian Dietary Guidelines recommend a woman planning pregnancy and during the first three months of pregnancy require a daily 400 μg (0.4mg) folic acid supplement in addition to foods naturally rich in folate.
In 2009 mandatory fortification of bread-making flour with folic acid was introduced in Australia with the aim to lower the incidences of neural tube defects in pregnancy. A survey conducted in 2011-12 found that woman were consuming ~530 μg/day, however it is currently too early to assess the impact of the fortification strategies.
MINERALS & TRACE ELEMENTS
The 2006 RDI recommend 27 mg/day during pregnancy, compared with 18 mg/day for non-pregnant adult females. Iron requirements in Australia have been set to a level that will absolutely require supplementation. This is largely because anaemia during pregnancy may compromise delivery of oxygen to the foetus and because the amount of iron required during pregnancy is greater than the iron stores of many women. The extra iron needed for a normal pregnancy, therefore, has to be provided mainly from external sources.
However, data exists that indicates that an intake of 27 mg per day may not be required to maintain iron stores during pregnancy. As gestation progresses, so does absorption rates. Moreover, the increase is large enough to meet the increased requirements of pregnancy provided that dietary intake is of the order of 18 mg per day. Iron absorption increases from an average of 7% at 12 weeks to 36% at 24 weeks and 66% at 36 weeks of gestation in subjects with normal iron status at the outset of pregnancy. In addition, the mother saves a total of 120 mg of iron due to an absence of menstruation.
Consequently, a normal dietary intake of 18 mg of iron is likely to be sufficient to meet the iron requirements of pregnancy in women with normal iron status, even without significant stores of iron at the outset of pregnancy.
The wonder of the female body is yet again reflected in its ability to cater for baby making in the calcium requirement department. The recommendation of calcium for adult females is 1,000 mg/day, which is the same for non-pregnant women. The foetus retains about 25-30 g of calcium, mostly in the third trimester, which is when foetal bone mineralisation occurs. There is evidence that pregnancy is associated with increased calcium absorption and accretion providing the minerals necessary for foetal growth without requiring an increase in maternal dietary intake or compromising long-term maternal bone health.
Additionally, oestrogen (also largely from the placenta) inhibits bone resorption and provides a compensatory release of parathyroid hormone which maintains the serum calcium concentration while enhancing intestinal calcium absorption and apparently decreasing its urinary excretion.
Once again, can I get a “hell yeah” for the female body?!
The RDI for zinc increases from 8 to 11 mg/day from adult females to pregnant women, respectively. The increase is based on the additional need for maternal and foetal tissues. The absorption rate is thought to be the same as non-pregnant women at 31%. Absorption is higher from animal foods than plant sources, so vegetarians will need intakes about 50% higher.
NB: For women taking high levels of iron supplements during pregnancy and lactation, the proposed EAR and thus RDI may not be adequate. There is some evidence that high levels of iron supplements prescribed to pregnant and lactating women may decrease zinc absorption.
Iodine is important in the production of thyroid hormones, which is increased in pregnancy by about 50%. The developing foetus is at greatest risk of iodine deficiency. Mild to moderate iodine deficiency can cause learning difficulties and affect physical development and hearing. The RDI for iodine during pregnancy is 220 μg/day. The National Health and Medical Research Council (NHMRC) recommends that all women who are pregnant, breastfeeding or considering pregnancy, take an iodine supplement of 150 μg/day to meet these requirements. The 2011-2012 Australian Health Survey reported that mean iodine intake was 152.6 μg/day for women aged 19-30 years and 153.2 μg/day for women aged 31-50 years.
So there you have it- a brief (albeit, long in blog-length terms), yet informative summary of the nutritional needs during pregnancy… or was it just a post about how wonderful the female body is? The feminist in me would say it’s more the latter, but I’ll let you decide.
Are you planning a pregnancy? Or if you’ve already had a child or two, what was your experience like, in terms of nutritional requirements? Did you have to make some changes to your food or supplement regime?
Australian Bureau of Statistics 1998, National nutrition survey nutrient intakes and physical measurements Australia 1995, ABS, Canberra, cat. no. 4805.0.
Australian Iron Status Advisory Panel 1997, Eating for a healthy pregnancy, AISAP, St Kilda West, Vic.
Butte, NF & King, JC 2005, ‘Energy requirements during pregnancy and lactation’, Public Health Nutrition, vol. 8, no. 7a, pp 1010–27.
Kramer, MS & Kakuma, R 2003, ‘Energy and protein intake in pregnancy’, Cochrane Database of Systematic Reviews, issue 4, art. no.: CD000032. DOI: 10.1002/14651858.CD000032. (New search for studies and content updated (no change to conclusions), published in Issue 3, 2010).
National Health and Medical Research Council 2006, Nutrient Reference Intakes for Australia and New Zealand including Recommended Dietary Intakes, AGPS, Canberra.
Prentice, A 2003, ‘Micronutrients and the bone mineral content of the mother, fetus and newborn’, Metabolism, vol. 133, no. 5, pp. S1693–S99.