Nutrients and calories in breast milk: A guide for the science-minded
© 2008 Gwen Dewar, Ph.D., all rights reserved
The nutrients and calories in breast milk may vary according to
• How many days a mother has been lactating
• The time of day
• Time elapsed since the beginning of a feed
• The mother’s diet
• The frequency between feedings
There are more than 200 constituents of breast milk known to
science. This article describes just a few of them. As laboratory
methods become more refined, new constituents are discovered.
Here I provide basic nutritional information, and offer tips for assessing and improving the quality of your milk.
Elsewhere, I discuss how the food you eat affects the flavor of your milk. For details, see this article about
early flavor experiences influence your baby's food preferences.
Basic nutritional information
According to a British report, each 100 mL of mature breast milk
(i.e., breast milk produced after 21 days of lactation) yields
• 70 calories
• 89.97 g water
• 7.4 g carbohydrates (primarily lactose)
• 4.2 g fat
• 1.3 g protein
These are the averages of samples taken repeatedly over a 24-hour period (Department of Health and Social Security 1988).
Within each breast, milk composition fluctuates during the day.
For example, fat content may vary by as much as 2g/L over 24 hours
(Institute of Medicine, National Academy of Sciences 1991, p. 118). This
causes significant variation in the calories in breast milk.
To some degree, milk composition varies by diet as well. The
numbers above reflect the average milk composition of British women.
Analyses carried out on other populations—consuming different diets—may
yield slightly different results. For instance, an analysis conducted in
India produced an estimate of 3.4 g fat per 100mL (Gopalan et al 2000).
But the greatest source of variation is found between individual women.
Within a given population, individual women may range in milk fat content from 2g/mL to 5g/mL (Institute of Medicine, National Academy of Sciences 1991).
Because fat constitutes the majority of calories in breast milk,
this means that some women produce more calorie-dense milk than others.
Moms producing fewer calories in breast milk will need to nurse their
babies more frequently.
Milk composition also varies over the course of lactation. Mature
breast milk looks very different from colostrum, the milk produced in
the first few days after birth. According to Guthrie (1989), each 100 mL
of colostrum yields approximately:
• 58 calories
• 5.3 g carbohydrates
• 2.9 g fat
• 3.7 g protein
Colostrum is low in fat and carbohydrates. As a result, there are
fewer calories in breast milk for the first few days of a baby’s life.
Colostrum is yellow because it contains high levels of beta carotene (10 times more than is found in mature milk).
Colostrum also contains elevated levels of vitamin E and zinc.
References: Nutrients and calories in breast milk
For very extensive information on the
nutrients and calories in breast milk,
I recommend Nutrition During Lactation. This volume is available
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