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Chapter 6

NUTR2050 Chapter 6: Chapter 6 Nutrition

Course Code
NUTR 2050
Simone Holligan

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Chapter 6—Nutrition During Lactation
- Helping women achieve appropriate nutritional status to optimize breastfeeding requires
consideration of energy and nutrient needs, weight goals, effects of exercise during
breastfeeding, and vitamin and mineral supplement needs .Multilevel (health care
system, community workplace, and family) support is critical for women who suffer from
common breastfeeding challenges and medical conditions. Human milk is the preferred
food for premature and sick newborns
Lactation Physiology
- The functional units of the mammary gland (the source of milk for offspring, also
commonly called the breast. The presence of mammary glands is a characteristic of
mammals) are the alveoli (A rounded or oblong-shape cavity present in the breast).
Each alveolus is composed of a cluster of cells (secretory cells—cells in the acinus,
milk gland, that are responsible for secreting milk components into the ducts) with a duct
in the center, whose job is to secrete milk. These branchlike collecting ducts lead to the
nipple. Myoepithelial cells (specialized cells that line the alveoli and can contract to
cause milk to be secreted into the duct) surround the secretory cells. They are contract
under the influence of oxytocin (A hormone produced during letdown that causes milk to
be ejected into the ducts) and cause milk to be ejected into the ducts.
Mammary Gland Development
- During puberty, the ovaries mature and the release of estrogen and progesterone
increases (table 6.1 page 165). The cyclic release of these two hormones governs
pubertal breast development (illustration 6.2). The mammary gland develops its lobular
structure (lobes—rounded structures of the mammary gland) under the cyclic production
of progesterone and is usually complete within 12-18 months after menarche. As the
ductal system matures, cells that can secrete milk develop, the nipple grows, and its
pigmentation changes. Fibrous and fatty tissues increase around the ducts. The lacteal
and placental hormones (placental lactogen and chrionic gonadotropin) allow further
preparation for breastfeeding. Estrogen stimulates development of the glands that will
make milk and progesterone allowes the tubules to elongate and the cells that line the
tubules (epithelial cells) to duplicate .
- Breast milk production or lactogenesis (another term for human milk production).
Lactogenesis 1 occurs during the first stage of milk production where milk begins to
form and the lactose and protein content increases and this stage extends through first
few days postpartum. Lactogenesis II begins 2-5 days postpartum and is marked by
increased blood flow to the mammary gland, and it is considered the onset of copious
milk secretion (when milk comes in). There are significant changes in both the milk
composition and quantity of milk produced and occurs over first 10 days of baby’s life.

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Lactogenesis III is when breast milk production begins about 10 days after birth and
this stage in which milk composition becomes stable.
Hormonal Control of Lactation
- Prolactin and oxytocin are necessary for stabling and maintaining a milk supply.
Prolactin is a hormone that stimulates milk production. Prolactin levels double with
suckling. Stress, sleep, and sexual intercourse also stimulate prolactin levels. To prevent
milk production in the last three months of pregnancy, prolactin activity is suppressed by
a prolactin-inhibiting factor that is released b the hypothalamus. This inhibition of
prolactin allows the mother’s body to prepare for milk production during pregnancy.
Oxytocin release is also stimulated by suckling or nipple stimulation. Its main role is in
letdown, or the ejection of milk from the milk gland (acinus) into the milk ducts. Oxytocin
also acts on the uterus, causing it to contract, seal blood vessels, and shrink its size.
Secretion of Milk
- The secretory cell in the breast uses 5 pathways for milk secretion. Water, sodium,
potassium and chloride are able to pass through alveolar cells membranes in either
direction (passive diffusion). Milk fat comes from triglycerides from the mother’s blood
and from new fatty acids produced in the breast. Fats are made soluble in milk by
addition of a protein. Immunoglobin A and other plasma proteins are captured from the
mother’s blood and taken into the alveolar cells. The proteins are then secreted into the
milk ducts.
The Letdown Reflex
- The letdown reflex stimulates milk release from the breast. The stimuli from the infant
suckling are passed through the nerves to the hypothalamus, which responds by
promoting oxytocin release from the posterior pituitary gland (illustration 6.4 p 167). The
oxytocin causes contraction of the myoepithelial cells surrounding the secretary cells. As
a result , milk is released through the ducts.
Human Milk Composition
- Human milk is an elegantly designed natural resource. It is only food needed b the
majority of healthy infants for approximately 6 months. The composition of milk is
designed not only to nurture, but also to protect infants from infectious and certain
chronic diseases. Hman milk composition is changeable. The basic nutrient composition
of colostrum and mature milk is provided in table 6.2 p 168.
- The first milk, colostrums (the milk produced in the first 2-3 days after the bab is born.
Colustrum is higher in protein and lower in lactose than milk produced after a milk supply
is established). It is a thick often yellow fluid produced during lactogenesis II (days 1-3
after infant birth). Infants may drink only 2-10mL (1.5-2 tsp) of colostrums per feeding in

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the first 2-3 days. Colostrum provides about 580-700kcal/K and is higher in protein and
lower in carbohydrate and fat than mature milk. Secretory immunoglobulin A and
lactoferrin are the primary proteins present in colostrums. The concentration of
mononuclear cells is highest in colostrums, and colostrums has higher concentrations of
sodium, potassium, and chloride than more mature milk.
- Breast milk is isotonic with plasma. This biological design of milk means that babies do
not need water or fluids to maintain hydration, even in hot weather. Water allows
suspension of the milk sugars, proteins, immunoglobin A, sodium, potassium, citrate,
magnesium, calcium, chloride, and water-soluble vitamins.
- Human milk provides approx .65 kcal/mL, although the energy content varies with its fat
(and to a lesser degree, protein and carbohydrate) composition. Breastfed infants
consume fewer calories than infants fed human milk substitute (HMS). Infants who are
breastfed are thinner for their weight at 8-11 months than infants fed HMS, but these
differences disappear by 12-23 months of age and few differences are notable by 5
years of age.
- Lipids are the second largest component of breast milk by concentration (3-5% in mature
milk). Lipids provide half of the energy of human milk. Human milk fat is low at the
beginning of a feeding in for milk, and higher at the end of the hind milk that follows.
Effect of Maternal Diet on Fat Composition
- When diets rich in polyunsaturated fats are consumed, more polyunsaturated fatty acids
are present in the milk. When a mother is losing weight, the fatty acid profile of her fat
stores is reflected in the milk. When every low-fat diets with adequate calories from
carbohydrate and protein are fed, more medium-chain fatty acids are synthesized in the
breast. Clinicians use the value of 20 kcal/oz of human milk to calculate energy provided
to an infant. Overall, the energy ranged from 20.9 to 26.2 calories per ounce.
- Milk DHA levels are increased by maternal supplementation. DHA is essential for retinal
development and accumulated during the last months of pregnancy. The advantages of
human milk seem particularly important to premature infants born before 37 weeks.
Advantages for term infants have been demonstrated as well.
Trans Fatty Acids
- Trans fat concentrations are similar in American and Canadian women, but lower in the
milk of women from European and African countries.
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