A comparison of infant formula and human milk in relation to obesity

Summary adapted from ‘The Duration, Frequency, and Volume of Exclusive Human Milk and/or Infant Formula Consumption and Overweight and Obesity: A Systematic Review’ by Dewey et al. 2020 This article was a systematic review of the literature aiming to determine the relationship between the duration, frequency, and volume of exclusive human milk and/or infant formula consumption and obesity. Childhood obesity has been rising rapidly and is a major public health concern. Identifying factors which are contributing to this rise is therefore of paramount importance and is a research priority. Infant formula has long been thought to contribute to increased weight gain and obesity in children, compared with breast milk. The studies included were those where healthy infants who were fed human milk and/or infant formula and were measured for being overweight or obese at 2 years of age or older. They also included sibling studies, where healthy siblings were fed differently during infancy and had rapid weight gain before 24 months or obesity measurements taken at 2 years of age or older. These sibling studies are included as they reduce the potential for genetic and environmental factors to bias the results, as the siblings presumably have similar genetic make-up and are raised in a similar environment. This resulted in 42 articles being analysed for the relationship between infant feeding and obesity in later life. Most of the studies examined weight status in infants who were fed any human milk compared to infants who consumed no human milk, or infants who consumed human milk for different durations. There was a moderate level of evidence to suggest that consuming any human breast milk is associated with a lower risk of being overweight or obese at two years of age and older. This effect is stronger still if human milk is consumed for 6 months or longer. This was consistent across the included observational studies. In studies conducted within families, analysing differences between siblings, some of the studies did not find a significant effect. This indicates that genetic or environmental factors may be influencing this relationship, rather than the effect being due to the infant feeding alone. Most of the studies being of observational nature (guardians decided milk regime themselves, rather than regime being randomised) and there were also concerns that studies conducted in the US would yield different results to other countries due to the higher prevalence of obesity. For these reasons, the evidence for this relationship was classified as moderate. There was not enough evidence to determine the effect of the duration of human milk consumption and obesity over 2 years of age. The same could be said for the relationship between the duration of exclusive milk consumption and obesity at over 2 years of age. The identified studies which investigated these relationships were inconclusive, meaning that some studies showed an association and others did not, therefore a conclusion could not be made. There was no evidence currently available to determine the relationship between the intensity, proportion, or amount of human milk consumed by infants fed with both human milk and infant formula and obesity at over 2 years of age. There was also no evidence regarding human milk consumed at the breast compared to by a bottle and obesity. No studies were identified for inclusion into these categories. This identifies an area to be prioritised for future research. In addition, it is noted that further sibling studies could reveal which genetic/environmental factors have an effect on obesity risk in relation to formula consumption and measures related to environmental factors such as parental obesity and socioeconomic status should be analysed in observational studies going forward. In conclusion, consuming any human breast milk likely reduces the risk of being overweight or obese at 2 years of age, compared to consuming only infant formula from birth. Other factors in this relationship, such as the duration, frequency and volume of consumption of either human breast milk and/or infant formula, could not be elucidated with the current research.