Maybe you should compare this to the percentage level of sugar (lactose) in human breast milk. Look it up and get back to us.
Human Milk Composition
Breast milk is the best food for the newborn. Human milk consists of 87% water, 1% protein, 4% lipid, and 7% carbohydrate (including 1 to 2.4% oligosaccharides) (Figure
1). It also contains many minerals (Calcium, Phosphorus, Magnesium, Potassium, Sodium, etc…) and many vitamins. Compared to cow's milk, human milk contains less protein (3.5% in cow's milk), and especially a proportion of casein (on total protein) lower, max 50% (80% in milk of cow). There is no β-lactoglobulin; some minor proteins are more abundant in human milk (lysozyme, lactoferrin,…) and the same goes for the non-protein nitrogen fraction (urea, free amino acids, including taurine). The protein content of human milk is therefore low (10 g/L), probably the lowest among all mammalian milks, and we can relate this observation with a very low growth rate of the newborn (for comparison, rat milk has a protein content 10 times higher for a growth rate of the pups also higher).
Another peculiarity of human milk is the highest proportion of long-chain polyunsaturated fatty acids (APGI-LC), ω6 (such as arachidonic acid) and ω3 (such as eicosapentaenoic and docosahexaenoic acids [DHA]), which are derived from essential fatty acids: linoleic and α-linolenic acid. These fatty acids are important for the brain development of the infant. Compared to cow's milk, breast milk also contains more cholesterol, which is a precursor of hormones and is also involved in brain development.
Finally, oligosaccharides are present in large quantities, from 10 to 20 g/L (only 1 g/L in cow's milk) and with very varied biochemical compositions (more than 100 different compounds) (role mentioned below).
Milk contains compounds that help protect children against infectious diseases (
13):
• Either by a direct immune protection, with the many immunoglobulins (including secretory IgA,…);
• Either by modulating this immune protection (by lactoferrin, pro or anti-inflammatory cytokines, or oligosaccharides);
• Either by a non-immune action, by proteins: κ-casein, α-lactalbumin, lactoferrin, haptocorrin, lysozyme (
14), and oligosaccharides (see below).
Colostrum, which is produced up to 5 days after birth, also contains many immunity cells (macrophages and lymphocytes).
Milk also contains enzymes including Bile Salt Stimulated Lipase (BSSL), which allows for better lipid digestibility, and better utilization of triglycerides (95% of total lipids), and presumably LC-PUFA, cholesterol, and fat-soluble vitamins.
A certain poverty of vitamins (D and K in particular) is known, whose consequences can be avoided by a supplementation of the children, even of the mothers during the pregnancy (vitamin D). In the same way, the presence in the breast milk of chemical contaminants, highlighted for some years, raises the question of their origin, namely via the nutrition and the environment of the mother (
15,
16) and their impact on the breastfed child. These contaminants accumulate in the body of the mother throughout her life because many are fat soluble and are found in adipose tissue. This is all the more pronounced since the first pregnancy of the mother is at an age more and more delayed. Preterm breast milk may also concerned by such contamination. The means to limit their presence in breast milk will be complicated to implement and will require societal, environmental and organizational policies over very long periods.
The richness of breast milk in miRNA is also one of its characteristics (
17,
18). MiRNAs are non-coding RNAs that regulate gene expression and control protein synthesis at the post-transcriptional level. They play roles in the regulation of many biological and developmental processes and would be important in the development of the child's immune system. Once the milk is ingested by the child, these maternal miRNAs resist digestion, when they are protected by cellular structures (exosomes). The question of whether they are subsequently absorbed and whether they regulate genes in children is a scientific issue that is still very controversial (
19).
Finally, the discovery of a microbiota of breast milk, from the 2000s, has led many teams to question its origin (endogenous entero-mammary or exogenous) and its relative role, compared to other microbiota (particularly maternal), in the colonization of the digestive tract of the newborn (
20,
21). There is no complete answer to all these questions, which are complex to solve and require sampling in the most sterile conditions and not to neglect all the necessary methodological controls. Added to this is the additional difficulty of elucidating the potential interactions between all these compounds: the effect of the content of oligosaccharides of breast milk on the microbiota of the newborn is thus well studied (
22), and makes it a good example of very current research.