This study found that the diets of older men and women who had been breastfed differed from those who had been bottle-fed, such that greater exposure to breast milk was associated with diets that were characterised by greater consumption of fruit, vegetables, wholemeal cereals and oily fish, and low consumption of refined cereals, sugar and full-fat dairy products. This association, whilst modest in terms of effect size, was robust to adjustment for confounding factors that included adult correlates of the dietary pattern, such as smoking and social class (18
). The lack of associations between type of milk feeding and other health behaviours suggests that the differences in adult diet are not simply a response to general recommendations for a healthy lifestyle, but that there may be specific effects of infant dietary exposures on food choices made in adult life. Additionally, independently of type of feeding, greater weight gain in the first year was related to differences in later diet; greater infant weight gain was associated with healthier dietary choices in adult life. To our knowledge, such differences in adult diet in relation to type of milk feeding and growth in infancy have not been described before.
There may be different mechanisms that link infant diet and growth to adult diet. In terms of infant diet, it is possible that differences in early exposures affect the acquisition of taste preferences, which influence later food choice. This would be consistent with experimental data from recent studies. For example, infants fed with bitter-tasting protein hydrolysate formula milks exhibit a greater preference for foods with the same sensory attributes in later childhood (26
). Breastfeeding exposes infants to volatile flavour compounds from the maternal diet. In comparison with infants who are formula-fed, these exposures are much more variable, which is likely to have a significant impact on flavour learning in infancy (11
). Although there is some recent experimental evidence that later acceptance of foods is greater among children who were breastfed (11
), this is difficult to assess, as the choice to breastfeed is also associated with differences in maternal education and diet (29
), and with differences in infant feeding practices (30
). In the present study, this was not the case, as the type of milk feeding in infancy was not associated with differences in social class or birth order – both factors that are known to be associated with differences in childhood diet (14
). Another possibility is that the observed differences in adult food choice according to milk feeding type resulted from differences in salt consumption in infancy as the relatively higher sodium content of cow’s milk, and early breast milk substitutes based on cow’s milk (32
), would have led to greater intakes in the infants who were bottle-fed. In animal studies, early exposure to salt enhances adult intake of sweet and salty compounds (33
). In this study, many of the foods that characterised the diets of the men and women with low prudent diet scores are high in salt (eg chips and processed meat) and sugar (eg added sugar, cakes & biscuits). However, when the consumption of individual foods in adult life was considered, there was little evidence of more marked associations between consumption of salty and sugary foods and milk feeding type.
The mechanisms that underlie the association between infant growth and adult dietary choices may include effects on early cognitive development. Brain growth is greatest in late gestation and in the first year of life (34
), and slow growth in infancy predicts poor cognitive performance in later life and lower educational attainment (35
). Batty and colleagues (37
) have shown that mental ability assessed in childhood is predictive of later food choices, such that children with higher test scores at age 10 have a greater consumption of fruit, vegetables and wholemeal bread and lower consumption of chips and white bread at the age of 30 years. The skills indicated by the cognitive tests, such as the ability to comprehend and reason, may affect the understanding of health messages and are therefore important for lifelong management of health behaviours. A recent review concluded that rapid infant growth does not lead to greater cognitive ability (38
). However, most of the studies included were of children born in recent decades. In this historical cohort, where the majority of children were breastfed, the significance of greater infant growth may be different. The observed association between greater weight gain and adult diet was robust, and was not changed by adjustment for a range of other factors. Whilst the data are therefore consistent with the possibility that greater weight gain in infancy was indicative of beneficial effects on brain growth and later cognitive function, there may be other explanations, as such effects would also be expected to lead to differences in the other health behaviours. In the present study there was no evidence of this.
A strength of this study is that a large population of older men and women were studied, for whom there was detailed contemporary information about infant feeding and growth. Although these data were not intended for future analyses, the categorisation of milk type is likely to indicate marked differences in exposure to breast milk, since feeding guidance in the 1930s recommended slow introduction of solid foods from around 8-9 months of age (24
). The high prevalence of breastfeeding in this cohort is consistent with other studies carried out in the 1930s (15
). Confidence in the feeding data is borne out by the observed dose effects in the association between milk type and weight gain in the first year, with greater weight gains in the infants who were bottle-fed (). This is consistent with known differences in the patterns of growth of breastfed and formula fed infants (35
). A weakness of the analyses is that there was no information on the type of milk substitutes fed to the men and women or on the duration of milk feeding in infancy, although the bottle-feeds are likely to have included commercial dried infant milks, unmodified cow’s milk and diluted condensed milk (24
). There is also no information on the nature of the participants’ weaning diets, which may have differed between breastfed and bottle-fed infants. However, these difficulties in assessing dietary exposures in infancy would be expected to cause misclassification and lead to attenuation of associations. It is therefore possible that the described association between adult diet and type of milk in infancy is underestimated.
In terms of the adult characteristics assessed, membership of this cohort was defined by area of birth, and there has been loss to follow-up. However, the participants’ characteristics are comparable with those of the wider community (17
) and the findings should therefore have relevance beyond the cohort. Diet was assessed using an FFQ that was administered by trained research nurses (18
). Although there is concern that FFQs can be prone to measurement error, they have been shown to define patterns in a comparable way to other dietary assessment methods (41
), and the patterns are predictive of biomarkers and a range of adult health outcomes (20
). A limitation of the analyses is that the examined associations were with current diet, and it will therefore be important to address the stability of the dietary patterns of the participants in an ongoing follow-up of the cohort. A further consideration is that although the analyses were adjusted for a number of factors, there may be other unmeasured influences on infant feeding practice and on adult dietary choice that were not assessed, and the possibility of residual confounding in these associations cannot be excluded.
Whilst the data suggest that differences in milk feeding and infant growth can have lifelong effects on food choice, it may be difficult to determine the relevance of these historical data for today’s children. For example the current composition of infant formula is very different from that of the breast milk substitutes available in the 1930s. Another key difference is the age at introduction of solid foods, which in the past was much later in infancy, and weaning may have been more gradual than it is today. Milk was therefore a relatively greater part of the infant diet. However, although comparable variations in dietary exposures may no longer exist, the findings are important. Firstly, they lend support to experimental findings, that early dietary exposures have long-term effects on taste preferences. Secondly, they suggest that such effects could impact on food choices throughout life. Although these data need to be replicated in other cohorts, they provide further support for current infant feeding guidance – to breastfeed, and to provide a varied weaning diet based on fruit, vegetables and home-prepared food. Appropriate infant feeding is important not only to support early growth and development, but may also be involved in establishing good food habits in later life.