Much of the published evidence in this area actually shows the opposite, that what a baby eats has nothing to do with their sleep. In 2015 we found that neither breast nor formula milk, timing of solids introduction, nor the amount of solids eaten affected how often babies woke up at six to 12 months.
The recent study is an excellent example of how statistically significant differences and real world differences can be miles apart. The authors themselves note that no difference in waking was seen until five months old, despite one group having solids from three months.
From then, babies in the early introduction group may have technically slept more, but this amounted to an average of just seven minutes more a night. At its maximum (six months old) the difference was 16 minutes. Most babies in the study still woke up once or twice a night whatever they were fed. And given these figures are based on the self-reporting of sleep deprived parents—which often does not match up to sleep recordings—this is not a basis for making major changes in infant feeding practices.
There is no physiological reason why introducing solid foods early would help a baby sleep. First, babies (after the first few weeks) do not simply wake at night because they are hungry. Just like adults, they wake because they are cold, uncomfortable or simply want comfort. The difference being that they cannot always soothe themselves back to sleep.
Second, even if it were for hunger, the most sensible solution would be to offer additional milk, as it will give more energy, fat and protein than any other food you can give a baby. The aim of the trial from which this data came was not to increase overall energy intake, but to test how introduction of allergenic foods at three versus six months affects the development of allergies (which it did not).
The parents were advised to give very small amounts of allergenic foods (such as one egg, 25g fish and 100g yogurt spread over a week—just a few spoonfuls a day) alongside rice, cereals, fruit and vegetables. All of these foods are lower in calories than breast or formula milk but take up more room, meaning babies might even eat a little less as they get used to weaning—a potential explanation for the larger sleep gap at six months as the standard group got used to food.
Less than half of the parents in the early introduction group stuck to the protocol. A variety of reasons were given but a major issue with introducing solids early is that babies are simply not physiologically ready. At three months, many may only just have good head control. They won’t be able to sit up properly. They still have a gag reflex that pushes food out of their mouth. Earlier introduction of solids can be messy, time consuming and demoralising, as babies simply aren’t equipped to be eating solids so soon.
Research shows that the earlier a baby is weaned, the longer it takes them to eat anything other than a few tastes. One study found if babies were given solids before four months it took them six weeks on average to eat just 100ml of food per day, but it was just 12 days for those weaned at the recommended six months.
The guidelines to introduce solid foods at six months are there for good reason. There is no deficit to growth or nutrient status in waiting until six months to introduce solid foods, but there is an increased risk of gastrointestinal and respiratory illnesses in infants given solid foods before then.
It should also be noted that the babies in the study were a very specific group. Nearly all were breastfed until six months old—97%, compared to just 34% in the UK population. Research shows that breastfeeding through introduction to solid foods is important in reducing allergy development, but often early introduction of solids increases risk of stopping breastfeeding.
Great care must be taken in generalising these findings. The research begs the question, does introducing solids early—with all its associated risks—really carry more weight if it comes with a few minutes of sleep every night? It seems to me that we should be asking why parents are struggling with sleep so much and seek better ways to support them instead.