Table of Contents
Consuming a healthy diet during pregnancy is an obvious and accepted recommedation. However, what exactly is a “healthy diet” in this context? In addition, there are specific nutrients which are crucial for the healthy development of the child, including nutrients which may be difficult to consume enough of. In addition there are nutrients and foods that need to limited or avoided during this period.
In this episode, researcher and dietitian Dr. Julie Abayomi discusses important nutrients in pregnancy (e.g. iodine, DHA, and folic acid), as well as potentially problematic nutrients/foods (e.g. high-mercury fish and caffeine). In addition, she discusses the current debates about weight gain/loss during pregnancy, as well as what supports are needed for health professionals supporting pregnant women.
Julie Abayomi, PhD, RD
Dr Julie Abayomi is a Reader in Dietetics & Associate Head of Applied Health & Social care at Edge Hill University. She is also currently the chair of The British Dietetic Association (BDA) England Board and an active member of the BDA Maternal & Fertility Nutrition Specialists group.
Dr. Abayomi is a registered dietitian, having worked in the NHS for over 20 years, with most of that spent specialising in women’s health and nutrition. In 2010 she was awarded a PhD based on research conducted at Liverpool Women’s hospital.
Dr. Abayomi’s research interests include: maternal nutrition, overweight and underweight in pregnancy; diabetes and pregnancy; diabetes and breastfeeding and chronic radiation enteritis.
Premium Feed Timestamps:
- [04.00] Dr. Abayomi’s background
- [06.30] Body mass & pregnancy
- [13.13] Is weight loss in pregnancy harmful?
- [18.50] Overview the most important micronutrients in pregnancy
- [21.30] Folic acid
- [25.50] Omega-3 and/or DHA
- [31.05] Iodine
- [38.00] Mercury
- [39.20] Caffeine
- [41.00] How can healthcare professionals be best supported?
- [46.49] Giving dietary advice based on what to include, rather than just exclude
Public Feed Timestamps:
- [05.00] Dr. Abayomi’s background
- [07.30] Body mass & pregnancy
- [14.13] Is weight loss in pregnancy harmful?
- [19.50] Overview the most important micronutrients in pregnancy
- [22.30] Folic acid
- [26.50] Omega-3 and/or DHA
- [32.05] Iodine
- [39.00] Mercury
- [40.20] Caffeine
- [42.00] How can healthcare professionals be best supported?
- [47.49] Giving dietary advice based on what to include, rather than just exclude
- Twitter: @julie_abayomi
- Pregnancy and Diet: BDA Fact Sheet
- Episode 418: Should We Consume a Direct Source of DHA?
This episode and topic is a pefect example of something that is at the crux of translating nutrition science into practice.
Whilst a solid understanding of the published evidence and the details of nutrient metabolism is important to the practitioner, in order to allow clients or patients to understand recommendations, and to implement them, the guidance needs to come in the form of food-based recommendations. And crucially, as Dr. Abayomi discussed, the need for positive recommendations for inclusions of certain foods, rather than merely a focus on exclusion or restriction.
In this episode, you heard us discuss one of Dr. Abayomi’s qualitative studies that found exactly this; i.e. pregnant women wanted more of the dietary advice to be aimed at what they should include, rather than simply the more common issue of being told what foods to limit or avoid.
So if we stick with today’s topic of diet in pregnancy, recall that there are nutrients that should be targeted at this time, as well as nutrients that should be limited or avoided.
Nutrients to consider:
- Folic acid
- Vitamin D
- Omega 3 (DHA)
The most common nutrient insufficiencies in women of reproductive age include:
In addition, for those on a plant-exclusive diet:
Nutrients to Limit:
- Usual suspects: saturated fat, salt, added sugars
- Vitamin A
- Non-approved supplements
But rather than tell the person you work with, to consume or avoid these nutrients, the more this can be translated into food-based terms, with practical steps (e.g. shopping for foods, meal recipes, etc.), the more likely these nutrient guidelines can be met.
So in relation to mercury, there is consistent and good communication in this area. [See the detailed study notes for a really nice image that presents recommended servings of different types of fish].
Similarly for things like iodine and omega-3, we can consider: a) what food sources can this person include? and b) what barriers are there for this person getting enough of said foods.
Detailed Study Notes
- NICE: National Institute for Health & Care Excellence. An institute in the UK that produces evidence-based guidance and advice for health, public health and social care practitioners. Such documents are often referred to as the NICE guidelines.
- DHA: Docosahexaenoic acid (DHA) is an omega-3 fatty acid
- Gestational Diabetes: High blood glucose that develops during pregnancy and usually disappears after giving birth. Can cause very real risks, and requires appropriate management.
- NHS: Refers to the National Health Service in England.
- Midwife: A midwife is a health professional who cares for mothers and newborns around childbirth, a specialization known as midwifery. The role can vary depending on the country, but in the UK and Ireland midwives are the lead health care professional attending the majority of births.
- Low birth weight: defined by the World Health Organization as less than 2.5 kg (~ 5.5 lbs)
- Antenatal: The period during the pregnancy.
- Postpartum/Postnatal: The period of time after the birth. Generally refers to the first 6 weeks after the birth of a baby. However, often when advice for ‘postpartum’ women is being discussed, it may refer to a longer period (e.g. up to the first year after the baby’s birth.)
Body Mass & Pregnancy
Typically, increased calorie intake is advised in pregnancy.
However, these is current discussion about how both energy targets and weight targets apply to those living with obesity.
Dr. Abayomi’s work has highlighted both the increasing prevalence in pregnant women who start their pregnancy living with obesity, and the increased risk that may put them at for complication, especially at very high BMIs.
One thing that was discussed in a previous episode with Prof. Leanne Redman (episode 402) was that maternal obesity increases the risk for adverse pregnancy and offspring outcomes; however, with large heterogeneity.
- “This variance in impact on the offspring adiposity in the future is not necessarily down to obesity per se, but rather is due to prolonged exposure to excess maternal substrates, namely glucose and triglycerides, which promote fetal fat accretion” – Flanagan et al., 2021
However, there seems to be a challenge here for both patients and practitioners: because what counts as “appropriate” weight gain across the pregnancy seems to differ by who you ask, or in many cases there just is no definition of this.
For example, there are no guidelines on the rate of weight gain by BMI in the UK or Ireland, so many professionals look to guidance given in the US by the Institute of Medicine guidelines.
However, there is disagreement about such recommendations. Concerns shared by Dr. Abayomi.
“The updated IOM recommendations have met with controversial reactions from some physicians who believe that the weight gain targets are too high, especially for women living with overweight or obesity. Also, these perceived high weight gain targets do not address concerns regarding postpartum weight retention. In addition, concerns have been raised that the guidelines do not differentiate degrees of obesity, especially for women living with class III obesity” – American College of Obstetricians and Gynecologists, 2013
Additionally, Most et al. (2019) published a prospective, observational study of pregnant women with obesity titled ‘Evidence-based recommendations for energy intake in pregnant women with obesity’ in which their findings suggest, contrary to current recommendations, energy intake should not exceed energy expenditure during pregnancy in these women.
It’s further complicated by the fact that a number of groups advise against weight loss during pregnancy (e.g. NICE guidelines), yet we have a situation where a patient could have reduced risk of complications at a lower level of adiposity. So this is clearly a complicated balance to strike.
For those who advise against weight loss in pregnancy, the evidence or rationale is typically based on harms of very restrictive diets. For example:
- Very restrictive diets are associated with metabolic ketoacidosis and renal dysfunction (Birdsall et al., 2009)
- Dutch Famine Study: 600 – 1500 kcal/d diets were associated with problems (Stein et al., 2004)
Nutrients of Focus in Pregnancy
A cross-sectional study by Charnley et al. (2021) found that intake of fibre and several key micronutrients (Iron, Iodine, Folate and Vitamin D) were significantly low.
Prospective cohort studies have indicated that dietary patterns high in fruit, vegetables, legumes, nuts, and fish, for up to 3 years prior to pregnancy are associated with reduced risk of gestational diabetes, hypertensive disorders, and preterm births.
In the UK there are two nutrients that are recommended to be supplemented with: folic acid and vitamin D.
Nutrients to consider:
- Folic acid
- Vitamin D
- Omega 3 (specifically DHA)
The most common nutrient insufficiencies (i.e., below the lower reference nutrient intake) in women of reproductive age between 18-42 include:
In addition, for those on a plant-exclusive diet:
70% reduction in risk for neural tube defects from folic acid supplementation in the 2-3 months prior to, and after, conception.
Neural tube defects (NTDs): The neural tube in the fetus develops into the brain and spinal cord. Neural tube defects occur when the brain, skull and/or the spinal cord and its protective spinal column do not develop properly within the first 4 weeks after conception. The most common NTDs are anencephaly (which results in stillbirth or death soon after delivery) and spina bifida (which may lead to a range of physical disabilities including partial or total paralysis). – via NICE Guidelines
In 96% of women across reproductive ages (defined as 18-42 in this study) had intakes of folate and iron below levels recommended specifically for pregnancy.
Higher doses recommended for: those with BMI above 30, those with a history of neural tube defects, or those with pre-existing diabetes.
Folic acid fortification in the food supply is now mandated in 87 countries globally, and this policy has been associated with reduced prevalence of neural tube defects in certain countries, but is currently not mandatory in Europe.
- The recommended folate concentration for pregnancy (>906nmol/L) is difficult to achieve through diet alone, and thus folic acid supplementation is recommended in addition to a folate-rich diet.
- However, the short-term time-course of effect for folic acid supplementation in planned pregnancy means that daily supplementation 3 months prior to conception appears sufficient to reduce risk, not only of neural tube defects, but low birthweight, miscarriage, and neonatal mortality.
- In women aged between 18 and 25 years old, 77% had iodine intakes below the LRNI.
- The World Health Organisation has stated iodine deficiency to be “the single most important preventable cause of brain damage” globally.
- Similar to folate, iodine is required in the preconceptual period due to the significant upregulation of thyroid hormone production in early pregnancy.
- This increased requirement resulted in the WHO increasing the recommended daily intake of iodine from 150 mcg/d for general reproductive years to 250 mcg/d during pregnancy and lactation.
- Iodine deficiency during pregnancy is associated with lower intelligence quotient (IQ) in offspring children, as well as other neurological and cognitive disorders.
- Evidence from intervention studies on iodine supplementation during pregnancy and cognitive outcomes in children is mixed, potentially reflecting differential thyroid health of the women, and iodine status of both intervention and control groups.
- The iodine contents of plant foods vary but on average tends to be low.
- In the UK, salt is not iodized, as it is in other places. So other fortification strategies may be needed.
- Fortification: dairy-alternative milk products sold in the UK are fortified with iodine equivalent to the amounts available in cows’ milk (25-50µg per 100ml). The amount from these products can vary by brand.
Omega-3 Fatty Acids & DHA
- The infant “brain growth spurt” occurs during the last trimester through the first 2 years of infancy.
- At this time, the long-chain polyunsaturated fatty acids docosahexaenoic acid (DHA) and arachidonic acid (AA) are preferentially incorporated into nervous system cell membranes.
- Although AA is essential in this lifestage, AA levels are maintained at a relatively constant level.
- But… maternal DHA levels are dependent on dietary intake.
- Overall, maternal DHA status appears to be the strongest predictor of cognitive development.
- It is possible that gestation has a greater influence on cognitive development than breastfeeding:
- greater umbilical cord DHA stores, not breastmilk DHA, have been associated with increased cognition at 11 months in full-term infants.
- Increased maternal DHA through supplementation at 600 mg/d has been shown to result in longer gestation duration and birth weight.
- This is supported by the observation that higher maternal DHA levels at birth correspond to increased maturation of attention and distractibility faculties in infants at 12 and 18 months.
- Advice may include consumption of a maximum of 2 servings (12oz total) of low-mercury oily fish, with additional supplementation of 200-300 mg/d of DHA.
- Without dietary DHA, an advised dose would be 600mg DHA/d from 20 weeks gestation.
- For more, listen to episode 418: Should We Consume a Direct Source of DHA?
- Studies conducted in the 1980s showed that profound vitamin D deficiency was associated with impaired fetal growth.
- Epidemiologic and case–control studies show a correlation between vitamin D deficiency and adverse pregnancy outcomes, not limited to fetal growth.
There is increased conversion to the active form of vitamin D in pregnancy:
- “By 12 weeks of gestation, 1,25(OH)2D levels are more than twice that of a nonpregnant adult and continue to rise two- to threefold from the nonpregnant baseline rising to over 700 pmol/l, attaining levels that would be toxic due to hypercalcemia to the nonpregnant individual, but which are essential during pregnancy” – Wagner et al., 2012
- Iron is a key nutrient during pregnancy that supports fetal development.
- Iron needs increase during pregnancy compared to prepregnancy.
- Iron deficiency affects about 1 in 10 women who are pregnant and 1 in 4 women during their third trimester. – Dietary Guidelines for Americans 2020 – 2025
- For women who are lactating, before menstruation returns, iron needs fall and then return to prepregnancy levels once menstruation resumes.
Nutrients To Limit
A number of nutrients may be problematic during pregnancy, if intake is too high. These include:
- Nutrients typically advised to limit for a healthy diet pattern: saturated fat, salt, added sugars
- Vitamin A
- Non-approved supplements (Hurst & Abayomi, 2018)
Why is Mercury an Issue?
- Mercury is well known as a potential harm to human health, when exposure is very high.
- It can be produced natural sources such as volcanoes, but more commonly is a by-product on industry processes; power plants, mining, waste incineration, etc.
- Mercury can exist in several forms, a number of which aren’t seen as much of a problem. If inorganic mercury is ingested by an animal for example, absorption is pretty poor. While elemental mercury doesn’t easilt cross tissue barriers.
- But mercury can also appear in lakes and oceans (via rainwater) and there it can be converted into methylmercury by microbes. And this form of mercury can be absorbed and transported into tissues.
- Therefore methlymercury can accumulate in fish who inhabit these lakes and oceans. And as humans may eat these fish, there have been concerns of potential harm raised.
- Despite very high exposure being a known hazard, the health impacts of a chronic, low-exposure to mercury (e.g. via eating fish) has not been as clearly determined.
What Levels are a Problem for Pregnancy?
- Due to particular risks in the peri-pregnancy period, the Environmental Protection Agency set methylmercury intake of 0.1 ug/kg per day as the allowable upper limit
- This is equivalent to a 50 μg/wk for a 70-kg woman
- This is calculated by taking the lower 95% confidence limit at which gestational exposure to mercury may produce abnormal neurologic test scores, and then multiplying that by a 10-fold uncertainty factor.
Guidelines for Fish Consumption in Pregnancy
- Mercury levels in fish are primarily dependent on species, with the highest concentrations in large predators (e.g. shark and swordfish), and very low levels in smaller or shorter-lived species (e.g. salmon and shellfish).
- EPA advises women of childbearing age, nursing mothers, and young children:
- To avoid shark, swordfish, golden bass, and king mackerel (each of these fish contain more than 50 μg of methylmercury per serving)
- To eat up to 12 oz/wk (~2 typical servings) of a variety of fish and shellfish lower in mercury, with a limit of 6 oz/wk of albacore tuna (30 μg methylmercury per serving.
Vitamin A is essential to the normal development of the embryo. And while insuffient vitamin A is still a major issue in the developing world, the opposite problem of excessive vitamin A is the bigger risk in developed countries.
“The main adverse effects associated with excessive vitamin A intake, particularly at the beginning of the first quarter of pregnancy, are congenital malformations involving the central nervous and cardiovascular systems and spontaneous abortion” – Maia et al., 2019
Due to the risks of excessive vitamin A intake, pregnant women should be aware of food sources rich in vitamin A:
- Multivitamin supplements containing excess retinol form of vitamin A
- Fish liver oils containing more than 700mcg/day
- Liver and liver products e.g. pate
- Consistent findings in prospective studies demonstrate that, comparing high to low caffeine intakes, higher caffeine intake during pregnancy is associated with low birth weight, with effects on gestational weight evident across all three trimesters.
- One meta-analysis also demonstrated a 21% relative risk increase (HR 1.21, 95% CI 1.08-1.37) for pregnancy loss from higher caffeine intake.
- Note: that the effect size was 10% (HR 1.10, 95% CI 1.01-1.19) for coffee itself indicates that the adverse effects are stronger for caffeine itself.
- These effects are generally observed with high – i.e., >4 cups coffee per day. So there may not be a risk at low caffeine intakes. However, exactly what the level is, is unknown.
- The discussion over any potential safe dose threshold for alcohol intake during pregnancy is controversial.
- Heavy maternal alcohol intake may result in fetal alcohol spectrum disorders with consequent adverse physical, behavioural, and learning effects.
- Given that the current evidence is not sufficient to exclude risk from low-moderate levels of intake, advice to limit alcohol intake during pregnancy is prudent.
From the BDA Fact Sheet – Foods to avoid or be careful with:
Improving the situation in healthcare; supporting practitioners and patients
A qualitative study exploring midwives’ perceptions and knowledge of maternal obesity: Reflecting on their experiences of providing healthy eating and weight management advice to pregnant women.
Three core themes were identified:
- “If they eat healthily it will bring their weight down”: Midwives Misunderstood
- “I don’t think we are experienced enough”: Midwives Lack Resources and Expertise
- “BMI of 32 wouldn’t bother me”: Midwives Normalised Obesity.