Influence of nutritional status of lactating mothers on breast milk’s volume and composition

Introduction

The lactation period is a major source of concern in developing countries because of its positive impact on the health and nutrition of infants. Lactating women from developing countries are considered nutritionally vulnerable groups because this period places a high nutritional demand on the mother. Inadequate maternal diet during this period will lead to poor secretion of nutrients in breast milk and this can have long term impact on the child’s health (Jones, Berkerly & Warner, 2010).

It is reported that a lactating woman should produce about 700 to 800ml of milk per day and this requires an extra energy need of about 500 calories per day. Women who are severely malnourished have reduced lactation performance, thus, the quantity of milk produced depends a lot on the mother’s diet. The diet consumed by the mother will not only fulfil her own nutritional needs but will also enable her to produce enough milk for her infant (Sylvia & Mary, 2012).

Nutritional status is an indication of the overall well being of a population. It has been reported that lactation has different effects on maternal nutritional status depending on its duration, intensity, as well as cultural diversity. In a cross sectional study, it was reported that breastfeeding when practiced either exclusively or otherwise had no significant negative effect on the nutritional status of the mothers. Likewise, a longitudinal study observed that irrespective of breastfeeding pattern, lactation also had no profound effect on maternal body composition. However, the high energy cost of lactation as well as the nutritional and health risk it could pose for the woman emphasizes the need for continuous monitoring of their nutritional status and dietary intake in poor resource countries (Allen, 2012).

Definition of lactation

The National Academy of Sciences/Institute of Medicine and Food and Nutrition Board (2009) defined lactation is the process of synthesizing and secreting milk from the breasts to feed young ones. It is an integral part in the physiologic completion of the reproductive cycle of mammals including humans. Human milk ensures the infants’ systemic protection, growth and development therefore breastfeeding is one of the most effective ways to ensure excellent child health and survival. It is the opinion of many paediatricians and obstetricians that – children should grow up knowing breastfeeding is the norm. And also, since the physiologic processes of breastfeeding are a normal part of the maturation of the female body, breastfeeding seems to have the attributes of a preventive health measure for women. Therefore, adequate breastfeeding support for mothers could save many young lives and ensure good health for mothers.

Breastfeeding is one of the most natural functions of a woman’s body, however considering the nutritive value of human milk and that the lactating mother will produce 20-30 ounces each day (about 850 ml), it becomes apparent to ensure that the mother receives good nutritional intake which will support the stamina that nursing an infant demands and that there is a need to educate lactating women and their families on widely acceptable variations so that dietary guidelines make minimal demands woman’s lifestyle while ensuring successful breastfeeding since parents can make decisions about feeding the infant(s) based on accurate information (ABM News, 2008).

Thompson and Manore (2005) stated that lactation is the result of well-coordinated effort of the hormones. Throughout pregnancy the placenta produces oestrogen and progesterone. In addition to performing various functions, these hormones prepare breasts physically for lactation and suppress prolactin during pregnancy. Towards the end of pregnancy, prolactin increases, ready for milk synthesis. The removal of the placenta at birth triggers the breast to respond to suckling by making milk. The maternal body prepares for lactation not only by developing the breast to produce milk but also by storing additional nutrients and energy. Lactation has profound benefits for the child as well as the mother and should be maintained for the wellbeing of both.

Nutrient requirement for lactating mothers

Brown (2008) in his book “Nutrition through Lifecycle” wrote extensively on nutrients needed by lactating mothers by stating that, good nutritional intake supports the stamina, patience and self- confidence that nursing an infant demands Helping women achieve appropriate nutritional status to optimise breastfeeding is important and requires consideration of energy and nutrient needs. Social support from husbands, mothers, sisters, healthcare providers, communities, employers and policy makers is also critical to breastfeeding success.

Nutrient requirements are considerably elevated during lactation than in any other stage of a woman’s reproductive life. Women who are breastfeeding should increase their energy and nutrient intakes to levels above those of non-pregnant, non-lactating women. The requirements are greater than during the pregnancy period, since breast milk has to supply an adequate amount of all the nutrients for an infant’s needs for growth and development. By four months after birth, an infant doubles the birth weight accumulated during the nine-month pregnancy period. The milk secreted in one month represents more energy than the total cost of a pregnancy.

Energy and nutrients can be obtained from a varied diet that includes foods from each basic food group. Some nutrient needs however are greater than others and they vary from pregnancy needs as they independently affect breast milk concentration. These needs are discussed in the section below.

1. Energy

Lactation is the most energy demanding phase of human reproduction. The energy cost of milk production in the first six months of exclusive breastfeeding increases women’s daily energy needs by 30% or 1260 kJ/day above the pregnancy energy requirement. This is worldwide accepted since the energy cost of lactation is presumed to be similar in well and poorly nourished women. However women in developing countries generally enter lactation with low bodily energy reserves, which makes them to be at risk of adverse nutritional consequences. How these women meet this need for additional energy has created considerable interest in terms of basic biology and policy implications (Brown, 2008).

The issue of energy saving adaptations to accommodate the cost of lactation where fat gains across pregnancy are low, has been addressed by various authors whose studies in developing countries revealed that intakes are often lower than those recommended, and that women in different populations use different strategies to cover the energy cost of milk synthesis (ABM News, 2008).

2. Macronutrients

A question often raised is whether a mother’s milk may lack a nutrient if she fails to get enough in her diet. The answer differs from one nutrient to the next, but in general, nutritional inadequacies reduce the quantity and not the quality of milk. Carbohydrates, protein and fat are building blocks for physical form. They break and reassemble into fuel, which our body uses to support physical activity and basic functioning. Women can produce milk with adequate protein, carbohydrate, fat and most minerals even when their own supplies are limited. For these nutrients and for the vitamin, folate as well, milk quality is maintained at the expense of the maternal nutrient stores (Thompson & Manroe, 2005).

a) Carbohydrates:

The three major types of dietary carbohydrate are starch, sugar and fibre. Many people regard starch and sugar as fattening and therefore to be avoided. Refined sugar is commonly blamed to cause Attention Deficit Disorder (ADD) and fibre is known as something to consume to avoid constipation. There is some scientific basis for each of the beliefs, although it is often exaggerated Intake of excess carbohydrate can cause weight gain, and only a small percentage of children with ADD are actually sensitive to sugar And only a certain amount of fibre is good. Too much can cause problems (Brown, 2008).

In lactation, carbohydrate intake is slightly increased by 80g/day from 130g/day recommended for pregnancy. Human milk has a very high lactose content (the principal carbohydrate in milk), about 7g/day and provides about 40% of energy to the infant. Human milk has a higher amount of lactose than cow’s milk, which makes human breast milk taste sweeter. In most studies, breast milk concentration appears to be insensitive to changes in the diet and nutritional status. However, carbohydrates are essential to provide the lactating mother with energy for the nursing period. Carbohydrates are also necessary in the diet to spare the utilization of body protein and prevent ketosis (Brown, 2008).

b) Proteins

Protein is a dietary essential that performs many functions in the body, i.e. structural components of body tissues (muscles, cartilage and bones), enzymes, hormones, components of the immune system transporters of other substances, membrane bound carriers and regulators of many biochemical processes. The primary role of dietary protein is to supply amino acids for biosynthesis, but it can be used for energy. Adequate protein intake is particularly important during periods of growth or recovery from disease (Dewey, 2014).

Protein needs during pregnancy increase to about 60g/day over the entire nine month period. This is an increase of 10 to 15g/day over the needs of a non-pregnant woman. In lactation a further increase of 15-20g/day above pre-pregnancy requirements is needed since protein is responsible for various functions, i.e. cell growth, tissue repair, energy source, maintenance of fluid and electrolyte balance, acid-base balance and a strong immune system (Adair & Popkin, 2012).

c.) Fats

The percentage daily energy that comes from fat does not change during pregnancy. However, they should not be totally avoided, since fat is essential for the new tissues and cells being formed arid in addition for foetus fat stores during the third trimester. Without adequate fat stores newborns cannot effectively regulate their body temperature. From late pregnancy to lactation more care should be taken on the type of fats consumed. Mono-saturated fats are important, but polyunsaturated fats that particularly contain omega-3 fatty acid known as docosahexaenoic acid (DHA), are of greater importance (Zareai, O’Brien & Fallon, 2007).

Though fat appears to be the most variable of the macronutrients within and between individuals, it is the main source of energy in human milk A breastfeeding woman has a higher requirement especially for DHA because her infant used a good deal of it for central nervous system development during pregnancy and also brain growth and eye development. The DHA content of maternal milk directly reflects maternal intakes. On average milk lipids comprise of about 4% of human milk. (Thompson & Manore. 2005).

3. Micronutrients

Maternal micronutrient status should be viewed on a continuum, from the preconception period, throughout pregnancy and lactation, for it determines pregnancy outcome, infant growth and development and maternal health. Multiple nutrient deficiencies can occur since the needs of several vitamins and minerals increase over the requirements of pregnancy and these include vitamin A, vitamin C, vitamin B, riboflavin (B₂), (B₁₂), biotin, copper, iodine, selenium, zinc, manganese and chromium. Inadequate dietary intake is considered one of the major causes of micronutrient deficiencies and ideally nutrient deficiencies should be prevented or treated before a woman becomes pregnant (Zareai et al, 2007).

In lactation, maternal status or the intake of the B vitamins (except folate), vitamin A, selenium, and iodine strongly affect the breast milk concentration of these nutrients. These can result in the infant consuming less than recommended and further depleting maternal stores that were low at birth.

The following micronutrients were considered in depth in this seminar work. They are the so- called key nutrients.

a) Calcium

Pregnancy and lactation are states known to be accompanied by physiologically up-regulated bone absorption in response to the calcium demands of the developing foetus and nursing infant. Calcium is a significant component of breast milk. As in pregnancy, calcium absorption is enhanced during lactation and urinary loss is decreased. In addition, some calcium appears to come from demineralization of the mother’s bones and increased dietary calcium does not prevent this. Thus the recommended intake for calcium for a lactating woman is unchanged from pregnancy; that is 1000mg/day. Because of their continual growth, teenage mothers should consume 1300mg/day. Typically if calcium is adequate, a woman’s bone density returns to normal shortly after lactation ends Breastfeeding has no harmful long-term effects on bones and teeth (Kasmussen & McGuire, 2010).

b) Iron

Iron is needed for psychomotor development, maintenance of physical activity and resistance to infection. Its deficiency develops when the intake of bio-available iron does not meet requirements or when excessive physiological or pathological losses of iron occur. Prevalence of iron deficiency varies greatly according to age, gender and physiological, pathological and socio-economic conditions. In pregnancy, iron deficiency is a risk factor for preterm delivery, subsequent low birth weight and possibly inferior neonatal health, whereas in breastfeeding women need less iron as compared to pregnant women. The requirements decrease from 27mg/day to merely 9mg/day, compared to pre-pregnancy amounts of 18mg/day. This is because iron is not a significant component of breast milk and in addition, breast-feeding usually suppresses menstruation for a few months minimizing iron losses (Kasmussen & McGuire, 2010).

c.) Zinc

Zinc is an essential mineral found in almost every cell. It stimulates the activity of approximately 100 enzymes which are substances that promote biochemical reactions in the body. It is beneficial for growth, maintenance of the immune function which enhances prevention and recovery from infectious diseases, maintains sense of taste and smell, and is needed for DNA synthesis (Allen, 2012).

Zinc deficiency most often occurs when zinc is inadequate or poorly absorbed, when there are increases in losses of zinc from the body or when the body’s requirement for zinc increases. There is no single laboratory test that adequately measures zinc nutritional status, therefore when clinical signs appear that are associated with zinc deficiency, a medical doctor has to be consulted for appropriate care.

Zinc and iron joint supplementation has been researched and is a great public health controversy today. These micronutrients have the potential to interact when given together; thus it is important to assess the biochemical and functional evidence from clinical trials before supplementation policies are established. Zinc is also known to interact with copper. In case of zinc toxicity, copper status is low; there is altered iron function, reduced immune function and reduced levels of high-density lipoprotein

The recommended amount of zinc during lactation is 12mg/day for women over 19 years and slightly higher than for pregnancy, which is 11mg/day It is important for mothers who breastfeed to include good sources of zinc in their daily diet and for the pregnant and lactating women to follow the doctor’s advice on taking mineral and vitamin supplements (Kasmussen & McGuire, 2010).

d.) Vitamin A

Infant liver stores of vitamin A at birth are very small even in well-nourished populations. They greatly depend on the dietary intake of the mother. On the other hand, although vitamin A in human milk decreases over the course of lactation, breast milk is a good source of vitamin A and clinical vitamin A deficiency is rare in breastfed infants during their first year of life, even in poor populations. Therefore, if mother does not consume vitamin A in her diet, she will be depleted together with her child (Jones, et al, 2010).

Vitamin A is essential for vision acuity, maintaining mucosal surfaces of the respiratory, gastrointestinal, and genitourinary tracts and for differentiation of immune system cells, however excess preformed vitamin A exerts teratogenic effects. The recommended dietary allowance in lactation is 850µg/day which gives a normal retinol concentration in breast milk of 485µg /litre Deficiency is caused by a habitual diet that provides too little bio-available vitamin A to meet physiological needs Estimates suggest that more than 80% of dietary intakes of vitamin A in Africa are from plant foods.

Vitamin A from animal foods such as dairy products, liver, eggs is preformed and the most bio-available dietary source, but that from plants, such as orange and green leafy vegetables, is in the form of pro-vitamin and has to be converted before absorption. Deficiency is common since a number of factors influence its conversion, and animal sources are expensive for resource poor households (Dewey, 2014).

e.) Thiamine (Vitamin B₁)

The RDA increment for thiamine during lactation is considerably higher than thiamine losses in milk; in part because the need for thiamine depends on energy intake, which is expected to be higher during lactation The predicted average thiamine intakes are less than the RDA only at lower than recommended energy intakes, suggesting that low thiamine intake is seldom a problem. Low maternal thiamine intake can result in low thiamine levels in milk, however intakes of at least 1.3mg/day (the RDA for non-pregnant, non-lactating women of 1.1mg/day plus an increment for milk secretion of 0.2mg/day) are desirable among women consuming 9207 kJ/day or less(Kasmussen & McGuire, 2010).

Thiamine deficiency results in the disease beriberi. Beriberi occurs in human milk fed infants whose nursing mothers are deficient. It also occurs in adults with high carbohydrate intakes mainly from milled rice and with intakes of anti-thiamine factors. Some cases of thiamine deficiency have been observed with patients who are hypermetabolic, are on parenteral nutrition, are undergoing chronic dialysis or have undergone gastrectomy. Because thiamine facilitates energy utilization, its requirements are expressed on the basis of energy intake, which vary depending on activity levels. Lactating women are estimated to transfer 0.2mg thiamine in their milk each day and an additional 0.2mg is estimated as a need for the increased energy cost of lactation of about 2092kJ/day (Kasmussen & McGuire, 2010).

f.) Riboflavin (Vitamin B₂)

Riboflavin converts to flavin mononucleotide (FMN) and further to flavin adenine dinucleotide (FAD) before these flavins form complexes with numerous flavoprotein dehydrogenases and oxidases. The flavoco-enzymes (FMN and FASD) participate in oxidation—reduction reactions in metabolic pathways and in energy production via the respiratory chain. Studies of riboflavin status in adults concluded that maternal riboflavin intake was positively associated with foetal growth in a sample of 372 pregnant women. The additional riboflavin requirement of 0.3mg/day for pregnancy is an estimate based on increased growth in maternal and foetal compartments (Zareai, et al, 2007).

Riboflavin deficiency results in the condition of hypo- or ariboflavinosis with sore throat, hyperaemia, oedema of the pharyngeal and oral mucous membranes, cheilosis, angular stomatitis, glosittis, seborrheic dermatitis and normochromic, normocytic bone marrow. For lactating women an estimated amount of 0 3mg riboflavin is transferred in milk daily and because of utilization for milk production is assumed to be 70% efficient, the value is adjusted upward to 0.4mg/day.

g.) Niacin (Vitamin B₅)

Niacin deficiency classically results in pellagra, which is a chronic wasting disease associated with a characteristic erythematous dermatitis that is bilateral and symmetrical, a dementia after mental changes including insomnia and apathy preceding an overt encephalopathy, and diarrhoea resulting from inflammation of the intestinal mucous surfaces.

Niacin content in human milk is approximately 1.5mg (12.3umol)/L and the tryptophan content is 210mg (1.0mmol)/L hence the total content is approximately 5mg NEs/L or 4NEs/0.75 L secreted daily in human milk. For lactating women, estimated 1.4mg preformed niacin is secreted daily, and an additional requirement of less than 1mg is needed to support the energy expenditure of lactation. Hence, 2.4mg N Es/day is the added need attributable to lactation (Zareai, et al, 2007).

h.) Vitamin C

Vitamin C (chemical names ascorbic acid or ascorbate) is a six-carbon lactone, which is synthesized from glucose by many animals Vitamin C is synthesized in the liver in some mammals and in the kidneys in birds and reptiles. Humans are unable to synthesize vitamin C.

Vitamin C has enzymatic functions where it acts as electron donor for eleven enzymes, but three of those enzymes are found in fungi and not in humans or other mammals. Vitamin C also protects low-density lipoproteins against oxidation and may function similarly in blood. A common feature of vitamin C deficiency is anaemia. Vitamin C promotes absorption of soluble non-heme iron possibly by chelation or simply by maintaining the iron in the reduced form. The antioxidant properties of vitamin C may stabilise folate in food and in plasma.

The populations at risk of vitamin C deficiency are those for whom the fruit and vegetable supply is minimal. Persons in whom the total body vitamin C is content is saturated can subsist without vitamin C for approximately two months before the appearance of clinical signs. As little as 6.5-10mg/day, vitamin C will prevent appearance of scurvy.

In general ‘vitamin C status will reflect the regularity of the fruit and vegetable consumption but also socio-economic conditions, because intake is determined not just by availability, but also by cultural preferences and cost. Low plasma concentrations are reported in patients with diabetes, and infections and in smokers but the relative contribution of diet and stress to these situations are uncertain Epidemiologic studies indicate that diets with high vitamin C content have been associated with lower cancer risk, especially cancers of the oral cavity, oesophagus, stomach, colon and lung. However, there appears to be no effect of consumption of vitamin C supplements on the development of colorectal adenoma and stomach cancer. Data on the effect of vitamin C supplementation on coronary heart disease and cataract development are conflicting (Lawrence & Lawrence, 2011).

During lactation 20mg/day vitamin C is secreted in milk. For an assumed absorption efficiency of 85%, the mother will need an extra 25mg. It is therefore recommended that the recommended nutrient intake (Nl) should be set 70mg to fulfil the needs of both the mother and the infant during lactation. The potential toxicity of excessive doses of supplemental vitamin C relates to intra-intestinal events and to the effects of metabolites in the urinary system. Intakes of 2-3g/day of vitamin C produce unpleasant diarrhoea from the osmotic effects of the unabsorbed vitamin in the intestinal lumen in most people (ABM News, 2008).

Vitamin C may precipitate haemolysis in some people, including those with glucose-6- phosphate dehydrogenase deficiency. People with the haptogolobin Hp2-2 phenotype condition may also have increased risk of red cell haemolysis (Kasmussen & McGuire, 2010).

i.) Water

It is widely assumed that milk production requires a high fluid intake on the part of the mother, yet the evidence suggests that lactating women can tolerate a considerable amount of water restriction and that supplemental fluids have little effect on milk volume. Lactating women who consumed no food or fluids from 0500hrs to 1930hrs during Ramadan lost 7.6% of their total body water and experienced increases in serum indices of dehydration, although values remained within the normal range. The milk volume was unaffected but changes in milk composition (lower lactose concentrations: increased osmolality due to higher electrolyte concentrations) indicated alterations in mammary cell permeability. Water turnover was very high, in part because the women apparently super hydrated themselves overnight prior to the fasting period

However, to protect herself from dehydration, a lactating mother should drink plenty of fluids. A sensible guideline is to drink a glass of water, milk or juice at each meal and each time an infant nurses. Despite misconceptions, a mother who drinks more fluid does not produce more breast milk (Steyn, 2006).

The influence of maternal nutrition on lactation

The effect of the nutrition of mothers on the quality and quantity of their milk is a frequent topic of discussion. However, studies conducted on this subject have shown that a mother’s nutrition has a greater impact on her long-term health than on the quality and quantity of her milk (Dusdieker, 2014).

Maternal nutritional status influence on milk volume

The mean volume of milk secreted by healthy women whose infants are exclusively breastfed during the first four to six months is approximately 750 to 800ml/day, but there is considerable variability from woman to woman and in the same woman at different times. The standard deviation of daily milk intake by infants is about 165ml; thus 5% of women secrete less than 550ml or more than 1200ml on a given day. The major determinant of milk production is the infant’s demand for milk, which in turn may be influenced by the size, age, health, and other characteristics of the infant as well as by his or her intake of supplemental foods. The potential for milk production may be considerably higher than that actually produced, as evidenced by findings that the milk volumes produced by women nursing twins or triplets are much higher than those produced by women nursing a single infant.

Studies of healthy women in industrialized countries demonstrate that milk volume is not related to maternal weight or height or indices of fatness. In developing countries there is conflicting evidence about whether thin women produce less milk than do women with higher weight for height. However, increased maternal energy intake has not been linked with increased milk production, at least among well-nourished women in industrialized countries.

Nutritional supplementation of lactating women in developing countries where under-nutrition may be a problem has generally been reported to have little or no impact on milk volume. However, most studies have been too small to test the hypothesis adequately and lacked the design needed for causal inference. Studies of animals indicate that there may be a threshold below which energy intake is insufficient to support normal milk production, but it is likely that most studies in humans have been conducted on women with intakes well above this postulated threshold.

The weight loss ordinarily experienced by lactating women has no apparent deleterious effects on milk production. Although lactating women typically lose 0.5 to 1kg per month, some women lose as much as 2kg per month and successfully maintain milk volume. Regular exercise appears to be compatible with production of an adequate volume of milk.

There is growing evidence that the volume of milk produced by women is primarily a function of infant demand and is unaffected by maternal factors such as nutrition, age, parity (except at very high parities) However, the influence of maternal intake of specific nutrients on milk volume has not been investigated satisfactorily. Early studies in developing countries suggest a positive association of protein intake with milk volume, but those studies remain inconclusive. Fluids consumed in excess of thirst do not increase milk volume (Lawrence & Lawrence, 2011).

Maternal nutritional status influence on milk composition

The composition of human milk is distinct from the milk of other mammals and from infant formulas ordinarily derived from them. Human milk is unique in its physical structure, types and concentrations of macronutrients (protein, fat, and carbohydrate), micronutrients (vitamins and minerals), enzymes, hormones, growth factors, host resistance factors, inducers/modulators of the immune system, and anti-inflammatory agents.

A number of generalizations can be made about the effects of maternal nutrition on the composition of milk as follows:

• Even if the usual dietary intake of a macronutrient is less than that recommended in Recommended Dietary Allowances, there will be little or no effect on the total amount of that nutrient in the milk. However, the proportions of the different fatty acids in human milk vary with maternal dietary intake.
• The concentrations of major minerals (calcium, phosphorus, magnesium, sodium, and potassium) in human milk are not affected by the diet. Maternal intakes of selenium and iodine are positively related to their concentrations in human milk, but there is no convincing information on this.
• The content of at least some nutrients in human milk may be maintained at a satisfactory level at the expense of maternal stores. This applies particularly to folate and calcium.
• Increasing the mother’s intake of a nutrient to levels above the RDA ordinarily does not result in unusually high levels of the nutrient in her milk vitamins B₆ and D, iodine, and selenium are exceptions Studies have not been conducted to evaluate the possibility that high levels of nutrients in milk are toxic to the infant.
• Some studies suggest that poor maternal nutrition is associated with decreased concentrations of certain host resistance factors in human milk, whereas other studies do not suggest this association.

(World Health Organization, 2008).

The advantages (benefits) of breast feeding.

For the infant

The benefits of breastfeeding to the infant include;

• It provides the appropriate composition and balance of nutrients with high bio-availability.
• Provides hormones that promote physiological development.
• Improves cognitive development.
• Protects against a variety of infections
• Protects against some chronic diseases such as diabetes (type 1) and hypertension late in life.
• Protect against food allergies.

For the mother

• Contract the uterus
• Delays the return of regular ovulation, thus lengthens birth intervals (It is not however a dependable method of contraception)
• May protect against breast and ovarian cancer

(World Health Organization, 2008).

References

ABM News (2008). World Breastfeeding Week 2008. London: ABM Press.

Adair, L.S. & Popkin, B.M. (2012). Prolonged lactation contributes to depletion of maternal energy reserves in Filipino women. J Nutr, 122(8): 1643-55.

Allen, L. H. (2012). B vitamins in Breast Milk: Relative importance of maternal status and intake and effects on infant status and function. Adv Nutr 3:362

Brown, J. (2008). Nutrition through Lifecycle (3^rd ed.). United Kingdom: Thompson Wadsworth.

Dewey, K.G. (2014). Impact of breastfeeding on maternal nutritional status. Adv Exp Med Biol. 554: 91-100.

Dusdieker, L. (2012). Is milk production impaired by dieting during lactation? American Journal of Clinical Nutrition 59: 833.

Jones, K., Berkerly, J. & Warner, J. (2010). Perinatal nutrition and immunity to infection. Paedatric Allergy and Immunology 21:564-576.

Kasmussen, K.M. & McGuire, K.M. (2010). Effects of breastfeeding on maternal health and well-being. Food and Nutrition Bulletin, Volume 17, Number 4, pp 318-321.

Lawrence, R.M. & Lawrence, R.A. (2011). Given the benefits of breastfeeding, what contraindications exist? Paediatric Clinics of North America, 48(1): 235-251.

National Academy of Sciences/Institute of Medicine and Food and Nutrition Board (2009). A report of the subcommittee on nutrition during lactation on nutritional status during pregnancy and lactation. California: National Academy of Science.

Steyn, N. (2006). Food and Beverages that make significant contributions to macro- and micro nutrient intakes of Children in South Africa-do they meet the food-based dietary guidelines? South African Journal of Clinical Nutrition 19: 66 -76

Sylvia, B. & Mary, D. (2012). The Nursing Mother’s Diet. The art of successful breastfeeding: A Mother’s Guide, New York: Sage Publications.

Thompson, J. & Manore, M. (2005).Nutrition: An applied Approach. New York, Pearson Corporation.

World Health Organization (2008). Evidence for the ten steps to successful breastfeeding, Geneva: WHO.