Fat and Energy Contents of Expressed Human Breast Milk in Prolonged Lactation

I read the article on fat content in breastmilk (1) in September’s Pediatrics with interest. It will be a useful article to quote since I am frequently in a situation of having to answer many paediatricians' beliefs that there is no nutritional value in breastmilk after 6 months, a year etc. As incredible as this sounds, it is a statement I hear not frequently from pediatricians.

However, I don't think the authors have considered one other possibility to explain the higher fat in the milk of women who breastfeed longer than a year (this I would consider a normal period of breastfeeding, incidentally, not "prolonged"). In most affluent, industrialized societies, support for breastfeeding is, shall we say, spotty. Indeed, if the slightest problems arise, mothers are often encouraged to stop or supplement, often when good help would avoid supplementing or weaning. From my knowledge of what goes on in Israel, I doubt the support for breastfeeding is better than here in Canada or the US or much of western Europe. Thus, the mothers who are still breastfeeding at a year or longer may have some advantage that results in their babies having few problems breastfeeding. One possible advantage may be a higher concentration of fat in their milk, which results in their babies growing quickly and the babies being content and happy. Thus, the results of this study would only mean something if the authors had followed the same mothers from early in lactation to later in lactation. The authors may answer that the mothers in the short duration group did not have as high CMT's as those in the normal duration group, but there is some overlap, isn't there? It would be interesting to see if the mothers with 12% CMT in their milk were more likely to breastfeed longer than those with 3%, say.

In the conclusion, the authors suggest that it is possible that the high concentration of fat in the milk might increase the risk of cardiac disease later on. This is quite a leap, for several reasons. First of all, most babies over a year who are not breastfeeding, are not drinking formula with low cholesterol, but regular cow's milk with high cholesterol. Secondly, though few studies have followed babies breastfed for over a year, many studies now show a decreased risk for breastfed babies of high blood pressure, type 2 diabetes, obesity, and LDL/HDL ratios, all suggesting they are protected against atherosclerosis (2-7). Citing an article following men who were born in the 1920's as a concern about cardiac disease makes no sense. These men would have been more likely, in those days, to have been breastfed or breastfed longer if they were in the lower socio-economic group, and several studies show increased risk of atherosclerosis in those in the lower socio-economic stratum. Jack Newman, MD, FRCPC Breastfeeding Clinic, North York General Hospital Toronto, Ontario M6P 3H6

1. Mandel D, Lubetsky R, Dollberg S, Barak S, Mimouni FB. Fat and energy contents of expressed human breast milk in prolonged lactation. Pediatrics 2005;116:e432-e435 2. Bergmann KE, Bermann RL, von Kries R, Böhm O, Richter R, Dudenhausen JW, Wahn U. Early determinants of childhood overweight and adiposity in a birth cohort study: role of breastfeeding. Int J Obesity 2003;27:162-72 3. Grummer-Strawn LM, Mei Z. Does breastfeeding protect against pediatric overweight? Analysis of longitudinal data from the centers for disease control and prevention pediatric nutrition surveillance system. Pediatrics 2004;113:e81 4. Pettitt DJ, Forman MR, Hanson RL, Knowler WC, Bennett PH. Breastfeeding and incidence of non-insulin-dependent diabetes mellitus in Pima Indians. Lancet 1997;350:166-8 5. Young TK, Martens PJ, Taback SP, et al. Type 2 diabetes in Children: prenatal and early infancy risk factors among Native Canadians. Arch Pediatr Adolesc Med 2002;156:651-55 6. Ravelli ACJ, van der Meulen JHP, Osmond C, et al. Infant feeding and adult glucose tolerance, lipid profile, blood pressure and obesity. Arch Dis Child 2000;82:248-52 7. Martin RM, Ness AR, Gunnell D, Emmett PE, Smith GD for the ALSPAC Study Team. Does breastfeeding in infancy lower blood pressure in children. Circulation 2004;109:1259-66

Conflict of Interest:

None declared

The report by Mandel and colleagues about the fat and energy content of expressed human milk in “prolonged” lactation (Pediatrics, Vol. 116, No. 3, 3 September 2005) provides as interesting a scientific analysis of the composition of human milk as it does a glimpse at the cultural bias from which the analysis is made.

Indeed, the authors’ very definition of “prolonged lactation” is at odds with the article’s last sentence, which appears to acknowledge the contribution of anthropologist Katherine Dettwyler to our collective understanding of the normal and natural – not the prolonged – duration of breastfeeding for modern humans: 2.5 years at a minimum and about 7 years at a maximum (1).

The article’s last sentence also provides a striking contrast to its first: “The optimal duration of breastfeeding is unknown.” Even if we don’t know yet, from the perspective of child-led weaning it is safe to say that at least the children do.

Unfortunately, the American Academy of Pediatrics’ open-ended recommendation – “Breastfeeding should be continued for at least the first year of life and beyond for as long as mutually desired by mother and child” (2) – has not been cited fully; whereas the World Health Organization’s policy – “while breastfeeding continues for up to two years of age or beyond” – has been omitted entirely (3).

That researchers are only just getting around to investigating human milk’s fat and energy content after one year of lactation speaks volumes about breastfeeding’s perceived nutritional and psychosocial value for toddlers. It also brings to mind, at the opposite end of the child-feeding spectrum, the widespread belief just a generation ago that human milk was fine but only for babies born at term; that is, until researchers took a look at the milk of mothers who actually delivered preterm and concluded that it was in fact better suited for babies born early (4).

The statement “Whether continued high saturated fat and cholesterol intake through breastfeeding beyond the first year of life is beneficial is unknown” only serves to reinforce the article's cultural bias. (Why wouldn’t it be? After all, breast milk is still milk.) Not so long ago pediatricians believed that breast milk was “deficient” in iron because it was “low” in iron, at least compared to infant formula. If breast milk is now seen as “high” in saturated fat, to what is it being compared? Milk’s fat content varies considerably among species, and even within the same species, for example the kangaroo that routinely produces two milks for different-age offspring. It’s time we adopted the perspective that what Mother Nature has provided is the default even as we strive to understand why.

We could also take a cue from the results of Australia’s first study of mothers who were breastfeeding children at least two years of age or older (107 mothers aged 21 to 45 years (average 34 years) and 114 children aged 24 to 78 months (average 36 months)). When children were asked about breastfeeding, nearly all said they breastfed because they liked the milk and it made them feel happy or good. They also reported that breast milk tastes “as good as chocolate” and “better than ice cream” (5).

James Akre, Geneva, Switzerland

References 1. Dettwyler KA. When to wean: biological versus cultural perspectives. Clin Obstet Gynecol. 2004;47:712-723. 2. American Academy of Pediatrics. Breastfeeding and the Use of Human Milk. Pediatrics, 2005;115:496-506. 3. Global Strategy for Infant and Young Child Feeding. Geneva, World Health Organization, 2003. 4. Lemons JA et al. Differences in the composition of preterm and term milk during early lactation. Pediatr Res., 1982;16:113-117. 5. Gribble K. Breastfeeding into toddlerhood and beyond: the experience of mothers and children. Breastfeeding the Natural State. Australian Breastfeeding Association International Conference, Hobart, 28-30 September 2005 (cited with permission).

Conflict of Interest:

None declared