Researching possible causes of rapid weight gain

When a child experiences rapid weight gain in her first 2 years of life, she runs a greater risk of growing up with excess weight - or even becoming obese. If ways can be found to avoid or lessen the incidents of rapid weight gain, it could help lower a child's risk of developing obesity later on in life.

Formula feeding is often seen as the culprit - but is this true? Parents and midwives need proper scientific evidence, so feeding decisions can be made based on more than hearsay.

In the article, Infant formula feeding practices associated with rapid weight gain: A systematic review, researchers looked at 18 papers that covered different aspects of formula feeding. This included studies looking into the protein content, the type of bottle used, and how parents feed their infant.

High or low protein

A study of formula-fed babies divided a group of 1,090 infants randomly - so roughly half of got a low protein formula, and the other high protein (with breastfed babies as a control group). The results showed more cases of rapid weight gain with higher protein levels than with lower protein formula (or breast milk).

High protein was measured as 2.05g/100ml from birth, and 3.2g/100ml for "follow-on" formula, given from 6 months. Low protein was 1.25g/100ml from birth, and 1.6g/100ml from 6 months. Breastmilk contains, on average, 1.03g/100ml protein - and is, therefore, considered low protein.

Though the authors are careful to note the need for further research, they do cite a study that suggests that lower protein formulas may lower the risk of rapid weight gain. Another study suggested no longer recommending "follow-on" formula, from 6 months, as a way of reducing the risk of rapid weight gain.

Extra calories

The calories in formula could also be an issue. Mixing formula incorrectly and making it more concentrated - or adding cereal to the formula - were both concerns that were researched.

A study investigating how parents mixed powdered formula found that more concentrated mixtures were associated with higher weights at 6 months. And although adding cereal to milk is not recommended due to choking risks, it also appears to lead to excess weight gain - with milk-cereal drink given at 6 months being associated with a higher BMI at 12 and 18 months.

Studying the bottle

Another aspect that could influence rapid weight gain is the baby bottle itself. The mere act of bottle feeding appears key to rapid weight gain - with more feeds per day linked to more weight gain, regardless of whether the bottle contained formula or mother's milk.

The size of the bottle also seems to make a difference. In this case, smaller could be better.  Babies fed with a large (±177ml) bottle showed more weight gain between 2 and 6 months than babies fed using a smaller bottle.

Putting baby to bed with her bottle also appeared to lead to early obesity by age 24 months.  And babies who tended to drink every last drop in their bottle - on their own, without parents' urging - were also more likely to gain extra weight. 

The researchers call for further study to firm up these findings, and to confirm other hypotheses about links between formula feeding and rapid weight gain. In the meantime, it is worthwhile taking the findings into consideration as opportunities to promote healthy weight gain among bottle fed infants.