Breastfeeding and Maternal Metabolism

Breastfeeding Basics

Breastfeeding provides numerous, truly profound, life-long benefits to you and your baby. When you understand the interconnected relationships between lactation, nutrition, and your metabolism, you will have the skills to succeed in nursing your infant and healthy weight management. Ideally, except in rare instances of supply insufficiencies, or other complications, infants should be exclusively breastfed for the first six months of life.

While myths still swirl about milk supply, such as how much water a new moms drinks, or what she eats, the actual factors that influence milk production include infant intake and nursing frequency, and maternal hormones, nutrition, and environmental impacts.

Suckling causes the production and release of the hormones prolactin and oxytocin. Prolactin, as its name implies, stimulates the production of breast milk. Oxytocin, our “feel good” hormone, is responsible for the “let down” effect, or the milk ejection reflex. Oxytocin also stimulates the uterus to contract and shrink back down in size, a process called involution.

It’s Alive, It’s Alive, It’s Alive!

Directly after childbirth, the initial breast milk is called colostrum, or pre-milk; a thick, yellow fluid that contains a higher amounts of white blood cells, antibodies, and Immunoglobulin A than mature breast milk. These living cells deliver essential health substances for the development of your infant’s immune and digestive systems.

On day one, about 100-ml/3.4 oz of colostrum is available in your breasts, and this quantity rises rapidly to about 500-ml/17 oz by day four. This is what we perceive as our milk “coming in.” Some factors, such as premature birth, diabetes, maternal obesity, retained placental fragments, or birth trauma may delay the rise in colostrum quantity.

 Breast Milk Supply

The amount of milk that a new mother makes is directly proportional to the amount of prolactin in her body. Since the nipple stimulation of suckling production produces prolactin, the amount, frequency, and intensity of early suckling determines breast milk supply. Therefore, separation of the mother and baby after birth, scheduled or restricted feedings, supplemental feeding with formula or water, or use of pacifiers are not advisable before breastfeeding has become well established.

The amount of breast milk that women make varies widely between 500 ml and 1200 lm per day. On average, milk production raises postpartum basal metabolism by about an average of 300 calories per day in the initial postpartum weeks. By four months, as infant intake increases, milk production raises maternal metabolism by about 400 calories per day and peaks at 500 calories per day by six months post childbirth.

Mothers of multiples can produce 2000 to 3000 ml of breast milk per day, which raises basal metabolism 1,000 calories or more per day.

Protecting Milk Supply

Careful management of breastfeeding in the first weeks after childbirth is critical for establishing adequate supply and ensuring optimal nutrition for your baby. Because supply is greatly determined by the infant factors of frequency, duration, and intensity, new mothers should feed “on demand” whenever her baby demonstrates signs of hunger. Full term infants nurse on average ten times per day or more in the first weeks of life. A minimum of eight feedings per day is necessary to provide enough hormone stimulation for successful breastfeeding.

As the infant’s need for milk increases, she may choose to feed more often, or increase the amount of milk consumed at each feeding.  Breast emptying is also a determining factor in milk production. Frequency is particularly important for mothers who wish to express milk.

Different babies have different feeding styles and these patterns can affect milk supply. Some vigorous older babies can consume adequate nutrition in just five feedings a day, whereas other prefer smaller feedings and need to nurse more often.

Other factors that influence milk volume include birth weight, gestational age at birth, and self-regulation. Larger babies are more likely to have greater suckling strength, and nurse more often for longer periods. Smaller full term infants may need to be fed more often to build adequate milk supply.

Since birthweight and gestational age are interrelated, preterm babies (born before 34 weeks) may not have sufficient suckling strength to nurse effectively. However, mothers of preemies can express milk for weeks, or even months if necessary, until their babies are able to suckle from breast.

Studies show that infants regularly take less milk from the second breast during feedings, which demonstrates the infant’s ability to regulate how much milk they consume per feeding.  Nursing mothers should get into the habit of alternating between which breast is offered first, and switch sides half way through feedings.

Maternal Influences on Milk Production

Tobacco and alcohol use, hormonal contraception methods, and severe energy restriction can all negatively affect milk volume.

Tobacco use has been shown to decrease infant weight, decrease milk production, and increase rates of infant illness and colic. Second hand tobacco smoke also exposes the infant to nicotine and it’s negative health effects.

Clearly, nursing mothers should not smoke or use tobacco products, but if they are not able to stop, they should still choose to breastfeed, as breastfed infants have reduced rates of respiratory illnesses as compared to their bottle fed counterparts.

Previously, doctors advised nursing mothers to consume alcohol, as it was though to have a relaxing effect that would assist in milk “let down.” However, studies now confirm the opposite effect; alcohol partially blocks the maternal milk ejection response and should not be used to facilitate nursing. Alcohol concentrations in breast milk can be found 30 – 90 minutes after consumption. The best advice for breastfeeding mothers is to refrain from alcohol. Nursing mothers who choose to drink alcohol should wait two hours after consumption before nursing.

Oral contraceptives, which combine estrogen and progestin, have been shown to lower milk volume and shorten the duration that mothers continue breastfeeding. Women who wish to use oral contraception and continue breastfeeding should consider progestin-only pills as an alternative.

Other contraceptives such as Norplant, Depo-Provera, and Cycrin are progestin compounds and have not been shown to reduce milk volume. Generally, these products are not prescribed until after six weeks postpartum.

While stress and anxiety are thought to negatively impact maternal breastfeeding management, little actual documentation exists to support this common belief.

Calorie Consumption and Breastfeeding

Maternal fat deposits support milk production in the early months of lactation. Since complaints of inadequate milk supply are found equally in both well-nourished and poorly nourished populations, energy balance is not thought to be an influencer in milk volume. Studies show that women in developing countries with chronic low energy intake have comparable milk volume to women from industrial countries with higher energy intake.

Among well-nourished women, a small, short study showed no impact on milk volume for those that consume a minimum of 1500 calories per day. However, reduced milk intake was observed in infants whose mothers consumed less than 1500 calories per day.

Although severe calorie restriction is widely regarded as detrimental for breastfeeding, there is limited data to support or deny this position. But to safeguard your supply, make sure to never go below 1500 calories a day while breastfeeding.

Healthy Weight Reduction and Breastfeeding

Studies show that maternal weight loss of about one pound per week yielded comparable quantity and quality of milk production to new mothers who did not restrict calories to induce weight loss. One pound per week equates to a daily deficit of about 500 below maternal metabolic balance point.

In the first six weeks after childbirth, eat a high quality diet to hunger. Give your body time to recover from pregnancy and childbirth, without the added stress of trying to lose weight. Then after the six weeks, if you want to lose weight while breastfeeding, aim to create a caloric deficit of between 300-500 calories on most days of the week. This will yield a slow and steady weight loss rate of about three to four lbs per month.

Extreme calorie restriction/rapid weight loss is detrimental to your body, as results in almost half the weight lost coming from lean mass, not fat reserves. Loss of lean tissue lowers basal metabolism, and negatively effects your body’s lean mass ratio, making long term weight management that much harder. Healthy weight loss always equals slow weight loss.

Breastfeeding Aids in Maternal Weight Loss

Average Infant Intake of Breast Milk and Maternal Energy Usage

Infant AgeAverage Infant IntakeMaternal Energy
1 month650 ml /22 oz day406 calories
3 months770 ml /26 oz day481 calories
6 months800 ml /27oz day500 calories
9 months740 ml/25 oz day462 calories
12 months520 ml/17.5oz day325 calories

Over the course of one year, the average daily increase in maternal metabolism is about 435 calories per day.  This amounts to a total of 158,775 calories, or about 45 pounds worth of additional energy, compared to women who formula feed their babies.

As you can see, breastfeeding dramatically assists in postpartum weight loss.

Exercise and Breastfeeding

Studies confirm that moderate level aerobic exercise, performed four or more days per week beginning after six weeks postpartum has no adverse effects on breast milk volume or composition, infant intake or growth rate, while providing significant improvement in cardiovascular fitness of the mothers.

Lactic acid, a byproduct of maximal intensity exercise, has been shown to alter the taste of breast milk, and may be less acceptable to some infants. Lactic acid levels drop significantly within 20 minutes post exercise. Exercise at 50 to 70% of maximal intensity (a perceived exertion rate of “somewhat” difficult) showed no increase in lactic acid levels in breast milk.

Though widely assumed, fluid intake is not correlated to breast milk volume. Instead, a decrease in maternal fluid intake concentrates urine, while milk volume remains stabile.

Exercise and successful exclusive breastfeeding are clearly compatible. However, exercise alone will not decrease your fat stores if you increase your calorie intake to compensate for the extra calories used during your workouts. 

New mothers who wish to lose weight can do so safely through a combination of modest calorie restriction and regular moderate level aerobic exercise (which increases fat mobilization) while protecting breast milk supply.

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