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 approximately

• 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 online. Auestad et al. 2001. Growth and Development in Term Infants Fed Long-Chain Polyunsaturated Fatty Acids: A Double-Masked, Randomized, Parallel, Prospective, Multivariate Study. Pediatrics 108 (2): 372-381

Auestad et al 2003. Visual, Cognitive, and Language Assessments at 39 Months: A Follow-up Study of Children Fed Formulas Containing Long-Chain Polyunsaturated Fatty Acids to 1 Year of Age. Pediatrics 112 (3): e177-e183

Ben Shaul DM. 1962. The composition of the milk of wild animals. International Zoo Yearbook 4: 333-342.

Bernhart FW. 1961. Correlations between growth-rate of the suckling of various species and the percentage of total calories from protein in the milk. Nature 191: 358-360.

Brenna TJ et al. 2007. Docosahexaenoic and arachidonic acid concentrations in human breast milk worldwide. Am J Clinical Nutrition 85: 1457-1464.

Department of Health and Social Security. 1988. Present day practice in infant feeding: third report: report of a Working Party of the Panel on Child Nutrition, Committee on Medical Aspects of Food Policy: Report on Health and Social Subjects 32. Her Majesty's Stationery Office, London.

Gopalan C, Ramasastri BV, and Balasubramanian SC. 2000. Nutritive value of Indian foods. Hyderabad, India: NIN, ICMR.

Guthrie AH. 1989. Introductory Nutrition. St. Louis, MO: Times Mirror/Mosby College Publishing.

Hadders-Algra M. Bouwstra H, van Goor SA, Dijck-Brouwer DA and Muskiet FA. Prenatal and early postnatal fatty acid status and neurodevelopmental outcome. 2007. Journal of Perinatal Medicine 35 Suppl 1: S28-34.

Institute of Medicine, National Academy of Sciences. 1991. Nutrition during lactation. Washington, DC: National Academy Press.

Jenness 1974. Biosynthesis and composition of milk. Journal of investigative dermatology. 63: 109-118.

Leeson CPM, Katterhorn M, Deanfield JE and Lucas A. 2001. Duration of breastfeeding and arterial distensibility in early adult life: population based study. BMJ 322: 643-7.

Makrides et al 1994. Fatty acid composition of brain, retina, and erythrocytes in breast- and formula-fed infants. Am Journal Clinical Nutrition 60: 189-194.

Mandel D, Lubetsky R, Dollberg S, Barak S, Mimouni FB. 2005. Fat and energy contents of expressed human breast milk in prolonged lactation. Pediatrics 116:e432-e435.

Mott GE, Jackson EM, McMahan CA, McGill HZ. 1990. Cholesterol metabolism in adult baboons is influenced by infant diet. J Nutrition. 120:243–251

Pond WG. 2003. Dietary Fatty Acids and Cholesterol in Normal Brain Development. Comments on Theoretical Biology, 8(1): 37-68.

Siimes MA, Vuori E, Kuitunen P. 2008. Breast milk iron--a declining concentration during the course of lactation. Acta Pædiatrica 68(1): 29 - 31.

Wang CD, Chu PS, Mellen BG, and Shenat JP. 1999. Creamotocrit and the nutrient composition of human milk. Journal of Perinatology 19(5): 343-346.

Woolridge MW. 1995. Baby-controlled breastfeeding: Biocultural implications. In: Breastfeeding: Biocultural perspectives. P. Stuart-Macadam and KA Dettwyler (eds). New York: Aldine deGruyter.

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