A healthy diet during pregnancy is essential to provide all the nutrients needed by a mother and her growing baby. It is a common misconception that pregnant women need to “eat for two”. In fact, most of the additional nutrients needed during pregnancy can be obtained by selecting appropriate foods and eating a high quality nutrient-dense diet. However there are some specific recommendations, which include taking folic acid supplements in early pregnancy to reduce the risk of neural tube defects, such as spina bifida. It is also important for pregnant women to be adopt good food hygiene practices to minimize the risk of food poisoning from harmful bacteria and to avoid substances in foods and drinks that might be potentially harmful to them or their growing baby.

Origins

The need for a healthy, balanced diet during pregnancy is well recognized and most dietary recommendations date back several years. For example, in the UK the Committee on Medical Aspects of Food Policy (COMA) set specific recommendations for nutrient intakes amongst the population as a whole and for pregnant women in 1991.However, in recent years

Recommended weight gain for pregnant women

If you are:	You should gain:
Underweight	About 27 to 40 pounds
Normal weight	About 25 to 35 pounds
Overweight	About 15 to 25 pounds
Obese	About 15 pounds or less

SOURCE:National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, U.S. Department of Health and Human Services

General weight-gain recommendations for women who are expecting only one baby. (Illustration by GGS Information Services/Thomson Gale.)

there has been heightened concern about the potential risks from exposure to certain substances, for example caffeine and alcohol, and greater support for the role that some nutrients can play in ensuring a successful pregnancy outcome. For example, it is now well recognized that folic acid supplements before and in the first trimester (first 12 weeks) of pregnancy can help to reduce the risks of neural tube defects (such as spina bifida).

Description

Although pregnant women do not have to “eat for two”, a healthy, balanced and varied diet that is rich in vitamins and minerals is important for both a mother and her baby. The mother’s diet must provide sufficient energy (calories) and nutrients to meet her usual requirements, as well as the needs of the growing fetus, and enable the mother to lay down stores of nutrients required for the baby’s development and for breastfeeding.

Pregnant women, as well as those planning for pregnancy, should follow a healthy, balanced diet. This can be achieved by following the usual guidelines, which are based around the five main food groups:

Bread, other cereals and potatoes. Foods in this group include breakfast cereals, pasta and rice. These foods should make up the main part of the diet. They are good sources of carbohydrate, protein and B vitamins, low in fat and filling. Whole-grain varieties contain more vitamins and minerals and breakfast cereals that contain added iron and folic acid are a good choice during pregnancy.
Fruit and vegetables. This includes fresh, frozen, tinned and dried varieties and fruit juice. It is recommended to consume at least five portions of different types each day (although fruit juice counts as only one portion however much is drunk in a day). Fruit and vegetables provide a number of important nutrients including vitamin C, beta-carotene, folate and potassium, as well as fibre.
Meat, fish and alternatives. Alternatives include eggs, nuts, pulses (such as beans, lentils, chickpeas) and textured vegetable protein. These should be consumed in moderate amounts and lower fat versions selected whenever possible. They are a major source of protein, vitamins and minerals. Atleast one portion of oily fish (e.g. sardines or salmon) a week will ensure an adequate supply of omega-3 fatty acids.
Milk and dairy foods. These should be consumed in moderate amounts and lower fat versions are preferable. These foods are particularly high in calcium and good sources of protein. Skimmed and semi-skimmed milk contain just as much calcium and protein as whole milk.
Foods containing fat and sugar. These foods add palat-ability to the diet but should be eaten infrequently.

Energy intake and weight gain

Energy (calorie) requirements increase during pregnancy by a small amount. The body’s increased need for some other nutrients, such as iron and calcium, can be met without increasing intakes. This is because the body adapts and becomes more efficient at absorbing and using these nutrients during pregnancy. However, for some nutrients, an increase in intake is necessary, including protein, the B vitamins - thiamin (vitamin B₁), riboflavin (vitamin B₂) and folate, and vitamins A, C and D. For some of these nutrients, such as for protein, the majority of women will already be consuming enough. However, for others, such as folate, dietary adjustments may be necessary in order to make sure that adequate amounts are consumed, and these are discussed in more detail below.

The total energy cost of pregnancy has been estimated at around 321 MJ (77,000 kcal). However, in reality, there are wide variations in individual energy requirements during pregnancy as women vary greatly in basal metabolic rate, body fat and physical activity levels. In the UK, the recommendation is for women to consume an extra 200 kcals per day during the third trimester only. But this assumes that women reduce their physical activity levels during pregnancy and women who are underweight or who do not reduce their activity level may require more. The American Dietetic Association recommends the additional energy needs during the second and third trimesters of pregnancy to be approximately 300 kcal per day in adults and older adolescents and 500 kcal per day in young adolescents (<14 years) but individual differences are also emphasised.

KEY TERMS

Basal metabolic rate— basal metabolic Rate is the number of calories the body burns at rest to maintain normal body functions.

DHA— A long-chain omega-3 fatty acid found primarily in oily fish. It is important for the development of the brain and the retina of the eye.

Folic acid— The synthetic form of the B vitamin folate, found in supplements.Folate is needed to produce red blood cells.

Iron deficiency anemia— The inability to make sufficient red blood cells that results in fatigue, shortness of breath, headaches and in ability to fight infections. It is common in pregnancy.

Low birth weight— A low birth weight infant is one who is born after the the normal gestational period (38-42 weeks) but weights less than 2.5 kgs (5.5 pounds) at birth.

Neural tube defects— Neural tube defects are serious birth defects that involve incomplete development of the brain, spinal cord and/or protective coverings for these organs.

Retinol— Also known as vitamin A. This is a fat soluble vitamin found in animal food sources.

A good approach is for pregnant women to eat when they feel hungry. If weight gain is appropriate, then energy intake is likely to be adequate.

For women with a healthy pre-pregnancy weight, an average weight gain of 12kg (range 10–14kg) is associated with the lowest risk of complications during pregnancy and labour and with a reduced likelihood of having a low birth weight infant. However women who are normally a healthy weight vary widely in the amount of weight they gain during pregnancy. Women who gain an excessive amount of weight are more likely to remain overweight or obese following the birth. But pregnancy isn’t a time for faddy diets or restricting food intake as this may lead to inadequate nutrient supplies for both the mother and fetus. Medical advice should be sought if there is concern about excessive weight gain during pregnancy.

Important nutrients

Folate is essential for the normal development of the neural tube in the fetus. The neural tube develops into the brain and spinal cord and closes between the third and fourth week after conception. Insufficiet folate at this crucial time can lead to serious malformations of the spine (spina bifida) and the brain (anen-cephaly). Folic acid supplements (400mg/day) are advised before conception and during the first 12 weeks of pregnancy because research has shown that they can reduce the risk of neural tube defects such as spina bifida by around 70%. Women who have already given birth to a baby with a neural tube defect should take a supplement that provides 5mg/day. Extra folate in the diet is also needed throughout pregnancy in order to prevent anaemia so pregnant women should also eat a diet that includes plenty of folate-rich foods (such as green leafy vegetables, oranges and pulses such as beans and lentils) and foods fortified with folic acid (such as fortified breakfast cereals). In the United States and Canada, fortification of flour with folic acid in recent years has greatly increased folate intakes. Although the number of babies born with neural tube defects has declined, this can not be attributed with certainty to increased folic acid intake.

Extra iron is needed during pregnancy, mostly in the last two trimesters. Inadequate blood iron levels causes iron deficiency anaemia which can make people feel tired, irritable and less able to concentrate. The risk of becoming anaemic is greater during pregnancy and anaemic women are more likely to deliver a baby of low birth weight and with poor iron stores. In the US, most recommendations advise pregnant women to take a supplement of 30 mg of ferrous iron as well as eating a well-balanced diet. In other countries, such as the UK, supplements are advised on an individual basis where considered necessary. However, pregnant women should eat plenty of iron-rich foods, such as lean red meat, pulses, dark green leafy vegetables and fortified breakfast cereals. Consuming foods containing vitamin C at the same time as non-meat iron-rich foods helps to enhance iron absorption. Examples include having a glass of orange juice (a source of vitamin C) with a bowl of cereal (containing iron) or baked beans (containing iron) with a baked potato (a source of vitamin C).

Vitamin D is needed to absorb calcium from the diet and an adequate supply is therefore essential for healthy bones and teeth. A vitamin D supplement of 10mcg/day is currently recommended for all pregnant women as a precautionary measure. Vitamin D is obtained mainly by the action of sunlight on the skin but is also found naturally in eggs, meat and oily fish. Most fat spreads are also now fortified with vitamin D.

DHA (docosahexaenoic acid) and EPA (eicosa-pentaenoic acid) are types of omega 3 fatty acids found in oil-rich fish (e.g. mackerel, salmon, kippers, fresh tuna, herring, trout and sardines). These are a major constituent of the brain and retina and there has been a lot of recent interest in their role in infant development. Eating fish has been associated with a lower risk of pre-term delivery and low birth weight. DHA and EPA can be made in the body from a type of polyunsaturated fatty acid called alpha-linolenic acid but it is not known how efficiently the body does this. Alpha-linolenic acid is found in oils (e.g. rapeseed, linseed, soya, walnut oils), nuts (e.g. walnuts, peanuts), grass-fed animals (e.g. beef) and green leafy vegetables (e.g. spinach).

Recommended dietary supplements

Apart from folic acid (400mg/day) and vitamin D (10mg/day), other vitamin and mineral supplements should not normally be necessary during pregnancy. However, if dietary intakes are thought to be inadequate, then a low dose multivitamin and mineral supplement can be taken as a safeguard. High dose supplements should be avoided, particularly those that contain vitamin A (retinol). There are now a number of specially formulated supplements available for pregnant women, and those planning to conceive.

The effect of diet on gastrointestinal symptoms and morning sickness

Indigestion, heartburn and intestinal discomfort are common, especially in late pregnancy when the baby takes up more space and squashes internal organs. Women usually learn by experience which foods to avoid and this is unlikely to lead to any nutritional problems unless it involves foods that are a major source of important nutrients (e.g. all meat or dairy products). Eating small meals, avoiding fatty and spicy foods may help.

Women who are experiencing constipation or haemorrhoids should increase the amount of fibre in the diet, by increasing intake of starchy carbohydrate foods, particularly whole-grain cereals and breads. An adequate fluid intake is also important, along with gentle exercise.

The causes of nausea and vomiting in pregnancy are not fully understood, although it has been suggested that changes in hormone levels or a heightened sense of smell may be involved. The experiences of individual women is very variable and can also differ with successive pregnancies. Some women find that the eating small, frequent meals can help to reduce nausea. Carbohydrate foods (e.g. bananas, toast, cereal, dried fruit), together with plenty of fluid are often the best choice. Some research has suggested that vitamin B₆supplements may help some women but there are concerns about the safety of high doses and women are advised not to take more than 5-10mg per day.

It is not unusual to have cravings for certain foods and aversions to other foods during pregnancy. The cause of these is also uncertain but may be due to altered taste perceptions. Dairy and sweet foods are most commonly reported as being craved and the most common aversions are to alcohol, caffeinated drinks and meats. As long as a healthy, varied diet is being consumed, there should not be cause for concern. Once the baby has been born, tastes usually return back to normal.

Food avoidance and risk of childhood food allergy

Infants whose parents have a history of allergic disease are more likely to develop allergies themselves and it has been suggested that by avoiding certain foods during pregnancy and breastfeeding mothers may help to prevent allergy in their infants. But there is little evidence to support this and others have suggested that exposure to these foods can actually help a baby develop tolerance to them. If there is strong family history of allergic disease (i.e. if either parent or a previous child has suffered from hayfever, asthma, eczema or other allergy), then it may be advisable to avoid peanuts or foods containing peanuts during pregnancy and while breastfeeding in order to reduce the risk of the infant developing a peanut allergy.

Food safety advice during pregnancy

Vitamin A

A high vitamin A (retinol) intake during pregnancy can cause birth defects. Pregnant women should therefore avoid liver and liver products, such as pate, as these foods can contain high concentrations of vitamin A and foods that are fortified with this vitamin. It is also recommended that supplements containing vitamin A (in the form of retinol), or high dose multivitamins are avoided, as well as cod liver oil supplements.

Alcohol

Drinking alcohol excessively or binge drinking during pregnancy can increase the risk of birth defects and low birth weight, as well as behavioural problems during childhood. The effects of lighter drinking on a developing child are less clear but to be cautious pregnant women are advised to avoid alcoholic drinks. If

QUESTIONS TO ASK YOUR DOCTOR

Would I benefit from taking a multivitamin and mineral supplement?
Am I gaining a healthy amount of weight?
Do I need to take iron supplements?

they choose to drink alcohol, intake should be reduced to a minimum (1-2 units once or twice a week). This is equivalent of half a pint to a pint of beer or lager or 1-2 small glasses of wine.

caffeine

Pregnant women should not consume excessive amounts of caffeine, as levels above 300 mg/day have been linked with low birth weight and miscarriage. Caffeine occurs in a range of food and drinks such as coffee, tea, cola and chocolate. In the UK, the Food Standards Agency recommends that pregnant women should not drink more than the equivalent of around four average cups of coffee a day.

Food-bourne illness

It is very important for pregnant women to follow general food hygiene guidelines when handling foods, especially raw meat. It is sensible to avoid foods which increase the risk of food-borne infections such as Listeriosis (e.g. unpasteurised milk, cheese made from unpasteurised milk, mould ripened cheeses which are usually soft or blue cheese) or salmonella poisoning (e.g. undercooked chicken, undercooked or raw eggs). It is also important to wash raw vegetables thoroughly as eating soil may cause toxoplasmosis.

Important foods to avoid to minimize the risk of foodbourne illness during pregnancy include:

Raw seafood (e.g. oysters, uncooked sushi)
Unpasteurised dairy products (these are unlikely to be sold by supermarkets but caution should be paid to exotic,smelly cheeses from the cheese counter)
Cheeses with a white mouldy rind (e.g. Brie, Camembert, Cambozola) and blue-veined cheeses (e.g. Stilton, Blue Brie, Danish Blue, Roquefort)
Pate (unless tinned)
Raw and undercooked meat and poultry (these should be cooked until there are no pink bits left, re-heat ready-cooked meals until piping hot)
Raw and undercooked eggs (eggs must be cooked until hard and foods containing raw eggs such as mousses and home-made mayonnaise avoided. Commercially prepared foods, made with pasteurised eggs, such as bottled mayonnaise are safe to eat)
Unwashed vegetables and salads
Liver and liver products (e.g. pate, liver sausage)

Contaminants in fish

Fish is a good source of protein, vitamins and minerals. In particular, oil-rich fish (e.g. mackerel, salmon, kippers, herrings, trout, sardines, fresh tuna) contain the long chain omega 3 fatty acids which are essential in brain and eye development in the fetus. However, fish can contain certain contaminants, namely mercury, dioxins and polychlorinated biphenyls (PCBs) and concern has been expressed about the consequences of prenatal exposure to these toxic chemicals on risk of brain and nervous system abnormalities.

High concentrations of methylmercury have been found in large, predatory fish such as shark, marlin and swordfish.These fish should be avoided during pregnancy and breastfeeding (in the US this also includes king mackerel and tilefish). Some samples of tuna have also been found to have higher levels than other species. In the UK, pregnant women (and those who may become pregnant) are advised to restrict their weekly intake to two 140g portions of fresh tuna or four 140g portions of canned tuna. The American Dietetic Association recommend a maximum of six ounces of albacore (white) tuna a week during pregnancy and that women restrict total fish consumption to 12 ounces of cooked fish per week (avoiding those listed above).

Oily fish can contain PCBs and dioxins. Because of the benefits of oily fish consumption, pregnant women are advised to follow the general advice for fish consumption in the UK and to consume at least two portions of fish per week, one of which should be oily. But to limit their intake to no more than two portions of oily fish per week. This advice also applies to women who might become pregnant and those who are breastfeeding.

Resources

BOOKS

Department of Health Dietary Reference Values for food energy and nutrients for the United Kingdom. Report on Health and Social Subjects 41. HMSO London, 2006.

Department of Health Report on Health and Social Subjects No. 50. Folic Acid and the Prevention of Disease 2000. Report of the Committee on Medical Aspects of Food PolicyThe Stationery Office, London, 2000

FAO/WHO/UNU Report of a Joint FAO/WHO/UNU Expert Consultation. Human Energy Requirements. FAO Food and Nutrition Technical Paper Series, No. 1, 2004.

Goldberg G Nutrition in Pregnancy and Lactation. In Shetty P (ed) Nutrition Through the Life Cycle. Leatherhead, Leatherhead Publishing, 2002.

PERIODICALS

American Dietetic Association. Nutrition and lifestyle for a healthy pregnancy outcome. Journal of the American Dietetic Association 102 (2002): 1470-1490.

Williamson, C.S. “Nutrition in pregnancy.” Nutrition Bulletin 31(2006): 28-59. Reprints of this briefing paper also available from www.nutrition.org.uk.

ORGANIZATIONS

American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, IL 60606-6995. Telephone: (800) 877-1600. Website: www.eatright.org. British Nutrition Foundaton, 52-54 High Holborn, London WC1V 6RQ. Website: www.nutrition.org uk Food Standards Agency, UK. Website: www.eatwell.gov uk Scientific Advisory Committee on Nutrition, UK. Website: www.sacn.gov.uk

Sara A. Stanner, MSc PHNutr

Preservatives seeArtificial preservatives

The Gale Encyclopedia of Diets: A Guide to Health and Nutrition