Dr. Greene's Answer
I applaud the critical thinking and intellectual curiosity of these scientists. When immunoglobulins were first discovered in breast milk, the appealing and simple conclusion was drawn that these immunoglobulins would directly improve the immune status of the baby. Indeed, specific antibodies against respiratory and intestinal bacteria and viruses are found in human breast milk. These have been thought to increase a child’s resistance to infection. Apparently the aforementioned scientists have pointed out that this reasoning is overly simplistic. In fact, the strong digestive enzymes in the infant and the acid bath awaiting the antibodies in the stomach would tend to denature and digest these antibodies, rendering them useless.
While I admire their reasoning and believe that this line of thinking deserves further exploration, there are currently no good studies that prove that a baby’s digestive process renders all antibodies inactive. In fact, there are some studies that suggest a baby’s immature digestive system may allow antibodies to make it through the stomach intact.
Regardless of the controversy surrounding the fate of antibodies in the stomach, there is plenty of evidence that shows that breastmilk benefits babies. Therefore, I vehemently disagree with the conclusion that breast milk is essentially no different from formula.
Many studies comparing the frequency of illness between breast- and formula-fed infants have demonstrated fewer illnesses and less severe illnesses in breast-fed infants (Garza et. al Special Properties of Human Milk, Clinics of Perinatology 14:11-32, 1987). While it is very difficult to separate all of the variables of parenting style and environment, mounting evidence shows a striking reduction in the incidence and seriousness of gastrointestinal infections, respiratory infections, and ear infections in breast-fed babies (Duncan et. Al Exclusive Breast Feeding for at Least Four Months Protects Against Otitis Media, Pediatrics 91:867-872 1993.) In evaluating the benefits of breast milk, the American Academy of Pediatrics conducted a review of the literature for evidence of disease reduction with the use of human milk. In their policy statement on breastfeeding, they found “strong evidence” that breast milk reduces the incidence and/or severity of diseases such as diarrhea, lower respiratory infections, ear infections, bacterial meningitis, and urinary tract infections. (American Academy of Pediatrics Policy Statement on Breastfeeding and the Use of Human Milk, Pediatrics 115(2):496-506, 2005)]. A review of data from the 1988 National Maternal and Infant Health Survey (NMIHS) showed that mortality rates are decreased 21% in breastfed infants beyond the newborn period (Pediatrics, 113(5):e435-e439, 2004). Other studies have shown a decrease in non-infectious diseases such as eczema and asthma. (Journal of Pediatrics, 139(2):261-266, 2001). If the immunoglobulins are rendered useless by digestion, how could this be?
There are many other ways that breastmilk benefits babies:
- Psychological factors: You mentioned that these scientists suggest that the only difference between formula and breast milk is psychological. I strongly disagree that this is the only difference, but I agree that the psychological difference can have profound implications. Over the last decade-and-a-half, the developing field of psychoneuroimmunology has demonstrated repeatedly that an individual’s psychological state has a direct effect on his or her immune function. Perhaps the nursing experience by itself does directly improve the immune status of infants.
- Immunoglobulins: All types of immunoglobulins are found in human milk. The highest concentration is found in colostrum, the pre-milk that is only available from the breast the first three to five days of the baby’s life. Secretory IGA, a type of immunoglobulin that protects the ears, nose, throat, and the GI tract, is found in high amounts in breast milk throughout the first year. Secretory IGA does its work before it is digested in the stomach. Secretory IGA attaches to the lining of the nose, mouth, and throat and fights the attachment of specific infecting agents. Breast milk levels of IGA against specific viruses and bacteria increase in response to a maternal exposure to these organisms. Human milk has been called environmentally specific milk — the mother provides it for her infant to protect specifically against the organisms that her infant is most likely to be exposed to.
- Lactoferrin: Lactoferrin is an iron-binding protein that is found in human milk, but is not available in formulas. It limits the availability of iron to bacteria in the intestines, and alters which healthy bacteria will thrive in the gut. Again, it is found in the highest concentrations in colostrum, but persists throughout the entire first year. It has a direct antibiotic effect on bacteria such as staphylococci and E. coli.
- Lysozyme: Human breast milk contains lysozyme (a potent digestive ingredient) at a level thirty times higher than in any formula. Interestingly, while other contents of breast milk vary widely between well nourished and poorly nourished mothers, the amount of lysozyme is conserved, suggesting that it is very important. It has a strong influence on the type of bacteria that inhabit the intestinal tract.
- Growth Factors: Human breast milk specifically encourages the growth of Lactobacillaceae, which are helpful bacteria that can inhibit many of the disease-causing gram-negative bacteria and parasites. In fact, there is a striking difference between the bacteria found in the guts of breast- and formula-fed infants. Breast-fed infants have a level of lactobacillus that is typically 10 times greater than that of formula-fed infants. Both the presence of the lactobacilli and the action of the lactoferrins and lysosomes help protect the infant by limiting the growth of unhealthy bacteria in the gut.
- Allergic factors: The cows’ milk protein used in most formulas is a foreign protein. When babies are exposed to non-human milk, they actually develop antibodies to the foreign protein. Research has shown that without exception the important food allergens found in milk and soybean formulas are stable to digestion in the stomach for as long as 60 minutes (as compared to human milk protein which is digested in the stomach within 15 minutes). The foreign proteins pass through the stomach and reach the intestines intact, where they gain access and can produce sensitization. While research in this area is still relatively new, this early exposure to foreign proteins may be the predisposing factor in such illnesses as eczema and asthma. The effects of early exposure to foreign protein are explored in three abstracts in the Journal of Allergy and Clinical Immunology, from January of 1996.
- Carnitine: While carnitine is present in both breast milk and formula, the carnitine in breast milk has higher bioavailability. Breast-fed babies have significantly higher carnitine levels than their counterparts. Carnitine is necessary to make use of fatty acids as an energy source. Other functions of carnitine have been hypothesized, but have not yet been proven.
- DHA & ARA: The main long-chain fatty acids found in human milk are now present in some, but not all formulas in the United States. These lipids are important structural components, particularly in the substance of the brain and the retina. Significantly different amounts of these ingredients have been found in the brains and retinas of breast-fed versus formula-fed infants. This difference may have other subtle effects on the cell membrane integrity in other parts of the body as well.
Apart from the specific properties that I have mentioned above, it is important to emphasize that breast milk is a dynamic fluid that changes in composition throughout the day and throughout the course of lactation. It provides for the baby the specific nutrients that are needed at each age and in each situation. The early data about breast milk was obtained from the pooled breast milk of many mothers. At that time it was not understood how unique human breast milk is for each individual infant (Lawrence, P.B. Breast Milk, Pediatric Clinics of North America, Oct. 1994). (Breast milk tastes different from feeding to feeding, which is another advantage over formula, as it prepares babies for the wide variety of foods to which they will be exposed in the future.)
The suggestions you heard from these prominent scientists serve as a good reminder that the mysteries of this dynamic fluid have not, by any means, been fully deciphered. Nevertheless, it becomes clearer year by year, that human milk is precisely designed for human babies. There may well be other important micro-nutrients or factors that we don’t even have instruments to measure yet. Not many decades ago, immunoglobulins were unknown. While formulas are an excellent alternative when breast feeding is not possible, human breast milk is the superior food for human babies for many, many reasons.