Human milk is a dynamic, bioactive fluid perfectly adapted to the nutritional, immunological, and developmental needs of the human infant. Its composition changes over time (colostrum → transitional → mature milk) and even within a single feed (foremilk → hindmilk).
1. Average Composition of Mature Human Milk (per 100 mL)
| Component | g/100 mL | kcal/100 mL |
|---|---|---|
| Water | 87–88 g | — |
| Total Energy | — | 65–70 kcal |
| Fat | 3.5–4.5 g | 31–40 kcal |
| Protein | 0.9–1.2 g | 4–5 kcal |
| Lactose | 6.7–7.8 g | 27–31 kcal |
| Oligosaccharides (HMOs) | 0.8–1.5 g | non-caloric (prebiotic) |
| Ash (minerals) | 0.2–0.3 g | — |
2. Major Chemical Components in Detail
A. Milk Fat (3.5–4.5 g/100 mL)
- 98–99 % triglycerides; high in long-chain polyunsaturated fatty acids (LCPUFAs)
- Key fatty acids: Oleic (C18:1), Palmitic (C16:0), Linoleic (C18:2), α-Linolenic (C18:3), ARA (arachidonic), DHA (docosahexaenoic) — essential for brain & retina development
- Fat globules smaller than in cow milk; surrounded by a complex milk fat globule membrane (MFGM) rich in glycoproteins and phospholipids
- Fat content increases dramatically from foremilk (~1–2 %) to hindmilk (~6–8 %)
B. Proteins (0.9–1.2 g/100 mL — much lower than cow milk)
| Type | Proportion | Key Proteins |
|---|---|---|
| Whey proteins (60–80 %) | Dominant | α-lactalbumin, lactoferrin, lysozyme, secretory IgA (sIgA), serum albumin |
| Caseins (20–40 %) | Minor | β-casein dominant; forms smaller, more digestible micelles |
Key bioactive proteins:
- Lactoferrin – iron-binding, antimicrobial
- Secretory IgA – first-line immune defense
- Lysozyme – antibacterial enzyme
- Haptocorrin – binds vitamin B12
C. Carbohydrates
Human Milk Oligosaccharides (HMOs) – 3rd most abundant solid component (0.8–1.5 g/100 mL)
- More than 200 different structures identified
- Indigestible by infant → feed beneficial gut bacteria (Bifidobacterium infantis)
- Act as prebiotics, anti-adhesives against pathogens, immunomodulators
D. Minerals & Trace Elements (total ash 0.2–0.3 g/100 mL)
| Mineral | mg/100 mL |
|---|---|
| Calcium | 20–35 |
| Phosphorus | 12–18 |
| Sodium | 15–30 |
| Potassium | 50–70 |
| Magnesium | 3–4 |
| Zinc | 0.1–0.3 |
| Iron | 0.03–0.1 (very low, but highly bioavailable) |
E. Vitamins
- High in vitamin A, E, C (especially in colostrum)
- Vitamin D low unless mother is supplemented
- All water-soluble vitamins present in adequate amounts
3. Types of Human Milk Over Time
| Type | Time | Fat | Protein | Lactose | Immune factors |
|---|---|---|---|---|---|
| Colostrum | 0–5 days | 2–3 g | 2–3 g | 5–6 g | Very high (IgA, lactoferrin) |
| Transitional | 5–14 days | Increasing | Decreasing | Increasing | High |
| Mature milk | >2 weeks | 3.5–4.5 g | 0.9–1.2 g | 6.7–7.8 g | Lower but still significant |
4. Quick Comparison: Human Milk vs Cow Milk
This comparison highlights the biological specialization of human milk versus cow milk:
| Component | Human Milk | Cow Milk |
|---|---|---|
| Energy (kcal/100 mL) | 65–70 | 60–70 |
| Protein (g/100 mL) | 0.9–1.2 | 3.2–3.8 |
| Lactose (g/100 mL) | 6.7–7.8 | 4.6–5.0 |
| HMOs | 0.8–1.5 g | Trace/none |
| Whey : Casein ratio | 60:40 to 80:20 | 20:80 |
| Calcium (mg/100 mL) | 20–35 | 110–130 |
| Iron bioavailability | High | Low |
| Bioactive factors | Thousands (HMOs, IgA, etc.) | Few |
Summary
Human milk is not just nutrition — it is a complete biological system. It has lower protein and mineral content than cow milk (protecting immature infant kidneys), higher lactose and unique oligosaccharides for brain growth and gut health, and hundreds of bioactive molecules that provide passive immunity, shape the microbiome, and program long-term health. No infant formula can yet replicate its complexity.
Related Topics
Chemistry of Cow Milk
Chemistry of Buffalo Milk
Chemistry of Goat Milk
Chemistry of Camel Milk
Chemistry of Sheep Milk
Chemistry of Donkey Milk