Human milk provides a complex and dynamic composition suited for human growth and development. While many animal milks are consumed, none can perfectly replicate human milk’s balance. This article compares animal milks to human milk to identify the “closest,” noting no perfect substitute exists for human infants.
The Distinct Composition of Human Milk
Human milk is a complex biological fluid, adapting its composition to meet the changing needs of a growing infant. It contains macronutrients like carbohydrates, proteins, and fats, for growth and energy. Lactose is the primary carbohydrate, around 6.7 to 7.8 grams per deciliter, providing energy and aiding mineral absorption. Fats, ranging from 3.2 to 3.6 grams per deciliter, are the most variable macronutrient and serve as a primary energy source, with a high content of palmitic and oleic acids for development.
Proteins in human milk, around 0.9 to 1.2 grams per deciliter, are divided into whey and casein fractions, with a higher proportion of whey protein (around 60%) compared to casein (around 40%). These proteins include types such as alpha-lactalbumin, lactoferrin, and secretory immunoglobulin A, along with non-protein nitrogen compounds. Human milk is also rich in many bioactive molecules, including antibodies, enzymes, hormones, and growth factors, important for immunity, organ development, and gut health. Colostrum, the milk produced in the first few days postpartum, is particularly rich in these components.
Nutritional Profiles of Common Animal Milks
Comparing animal milks to human milk reveals differences in their nutritional makeup, reflecting the growth needs of each species’ offspring. Cow milk, a common animal milk, contains higher protein content, around 3.3 grams per 100 ml, more than double human milk’s 1.3 grams per 100 ml. This higher protein content is suited for calves, which grow much faster than human infants. The fat content in cow milk is comparable to human milk, but fatty acid types differ, with cow milk having more saturated fat and human milk having more unsaturated fat, important for brain development. Cow milk also has a lower lactose content (around 4.5-5%) compared to human milk (around 7%).
Goat milk, another alternative, also has higher protein and fat content than human milk, with protein levels around 3.15 grams per 100 ml and fat around 3.97 grams per 100 ml. Its lactose content is lower than human milk, similar to cow milk. Camel milk contains higher fat and protein (especially casein) but lower whey protein and lactose than human milk. Donkey milk, in contrast, shows closer similarities to human milk in protein content, which is lower (1.5-1.8 g/100g) than cow milk, and a similar high lactose content (5.8-7.4%). Mare’s milk also shares similarities with human milk in protein and lactose, though its fat content is lower than human milk.
Regarding micronutrients, human milk has lower concentrations of minerals like calcium, phosphorus, sodium, and potassium compared to cow, goat, and camel milk. For example, cow milk contains nearly four times the calcium of human milk. Human milk has higher levels of copper and more vitamin C than cow milk. Donkey milk has a vitamin C content similar to human milk (57 mg/L compared to human milk’s 60 mg/L) and higher levels of B-complex vitamins.
Beyond Basic Nutrients: Immune Factors and Digestibility
Human milk contains bioactive components that animal milks largely lack or contain in different quantities. Human milk is rich in immune factors such as secretory IgA, lactoferrin, and lysozyme, which provide protection against infections and inflammation. While lactoferrin and lysozyme are present in some animal milks like donkey milk, their levels are lower or differ from those found in human milk. Human milk also contains live cells that promote infant development, elements not found in processed animal milks.
The structural differences in proteins and fat globules in animal milks impact their digestibility for human infants. Cow milk, for instance, has a higher proportion of casein to whey protein (80:20) compared to human milk (40:60), and its casein forms a tougher, less digestible curd in the infant stomach. The fat globules in cow and goat milk are larger than those in human milk, affecting digestion and absorption. In contrast, donkey milk has small fat globules, similar to human milk, which contribute to easier digestibility. Proteins in goat milk are more easily digested than those in cow milk, and goat milk also contains smaller fat globules.
Evaluating the Closest Animal Milk
Based on nutritional components and bioactive factors, donkey milk and mare’s milk are considered the most similar to human milk. These milks share similarities with human milk in their lower protein content, with lower casein and higher whey proteins, making them more digestible than cow milk for human infants. Both have similar lactose levels to human milk. The fat in donkey milk is lower than human milk, but its triglyceride structure and small fat globule size are similar, facilitating easier digestion.
Each species’ milk is uniquely adapted to meet the developmental needs of its own offspring. Human milk’s dynamic composition, precise nutrient balance, and array of bioactive compounds cannot be fully replicated by any animal milk. While certain animal milks, like donkey or mare’s milk, offer closer nutritional profiles, they still lack the biological complexity and species-specific benefits of human milk. Commercial infant formulas are designed to mimic human milk composition more closely than raw animal milks, providing a more appropriate alternative when human milk is unavailable.