Recent health issues reported in the British media have included the link between consumption of red and processed meat with an increased risk of cancer and the need for a ‘sugar tax’ to curb the ever-increasing rates of obesity and its associated health problems. These are big, newsworthy issues relating to the effect of diet and lifestyle on health: the World Cancer Research Fund estimate that around 6,000 cases of bowel cancer in the UK could be prevented by reducing consumption of red and processed meat, while a 20p/litre tax on sugar-sweetened beverages could reduce the number of obese adults in the UK by 180,000 according to the Faculty of Public Health.
So one has to feel a little pity for a journalist tasked with writing a piece about a study investigating whether the composition of a mother’s breast milk was associated with infant weight and body composition. The journalist from The Times seemed to approach this task by jumping on the obesity bandwagon; two key quotes from the story are: “A mother’s milk can increase the chance of a child growing up obese” and “A study … identified sugars in breastmilk that heightened a baby’s risk of being overweight by the age of 6 months”. This seemed to fly in the face of almost everything I had ever read about breastfeeding, so I decided to look at the evidence in a bit more detail.
The paper was based on a sample of 25 breastfeeding mothers and their babies. No babies were formula-fed. Outcomes were infant growth (weight and length) and body composition (percentage fat, total fat and lean mass). Whether or not the baby was ‘overweight’ or ‘obese’ was not an outcome. An association between the level of different human milk oligosaccharides (HMOs) in breast milk and infant weight and body composition was identified by the study authors, adding to the evidence base regarding the factors influencing a baby’s growth and development. The authors themselves made no direct claim that breastfeeding causes childhood obesity (three separate meta-analyses have, in fact, shown the opposite [4-6]), with the smallest of these studies including data for almost 30,000 babies.
The journalist’s train of thought may have gone thus:
The first step in this chain was identified by the study authors. But was the journalist justified in making the second?
The increase in risk of adulthood obesity given a high weight-for-age percentile in infancy has been known for some time, so the second link is plausible. But can it automatically be inferred from this study? To do so relies on the increases in body fat/fat mass being of such magnitude to class some of the infants in this study as overweight or obese at six months and we simply don’t know if this was the case. Instead, it could be possible that babies receiving alternative combinations of HMOs to those shown in the diagram were actually underweight and that those at the upper end of the weight range were still of ‘normal’ weight. We also don’t know how the weights and body compositions of the babies in the study would compare to those who have been formula-fed: even if breast milk containing high levels of certain HMOs did increase the risk of obesity, the risk with such HMOs could still be lower than that from infant formula.
That some HMOs were shown to have a negative relationship with body weight and/or composition seemed to make the journalist even more confused, since the story ended by stating “However, scientists also found that breast milk could protect against obesity.” The meta-analyses quoted above have demonstrated this, but once again, such a conclusion cannot be drawn from this particular study.
Reporting of current research in the media is invaluable to help increase uptake of its findings, yet the dangerous misinterpretation of the findings of the study by Alderete et al. mean that I hope the story in The Times (not the research study) was ignored by all who read it.
— Celia Taylor
- World Cancer Research Fund. Bowel cancer. 2015. [Online]
- Faculty of Public Health. A duty on sugar sweetened beverages. A position statement. 2013. [Online]
- Alderete TL, Autran C, Brekke BE, et al. Associations between human milk oligosaccharides and infant body composition in the first 6 mo of life. Am J Clin Nutr. 2015. [ePub].
- Arenz S, Rückerl R, Boletzko B, von Kries R. Breast-feeding and childhood obesity – a systematic review. Int J Obesity. 2004; 28: 1247-56.
- Owen C, Martin R, Whincup P et al. The effect of breastfeeding on mean body mass index throughout life: a quantitative review of published and unpublished observational evidence. Am J Clin Nutr. 2005; 82: 1298-1307.
- Harder T, Bergman R, Kallischnigg G et al. Duration of breastfeeding and risk of overweight: a meta-analysis. Am J Epidemiol. 2005; 162:397-403.
- Charney E, Goodman HC, McBride M, et al. Childhood Antecedents of Adult Obesity – Do Chubby Infants Become Obese Adults? N Engl J Med. 1976; 295: 6-9.