Nutrition- and feeding practice-related risk factors for rapid weight gain during the first year of life: a population-based birth cohort study

The global prevalence of childhood overweight and obesity has grown dramatically in recent decades [1], and even the youngest age groups are affected [2]. The “first 1,000 days” of a child’s life, beginning at conception and ending on their second birthday, has been identified as an important period for the establishment of obesity and associated diseases affecting life-long health [3].

One identified risk factor for later overweight that has gained much attention in recent research is rapid weight gain (RWG), seen as upward centile crossing in weight growth charts and defined as a change > 0.67 in weight standard deviation scores (SDS) [4, 5].

RWG during the first two years of life has in a number of studies been associated with overweight or obesity in both childhood and adulthood [3‐5]. One review revealed that 45 of 46 studies reported a positive association between higher infancy weight or RWG and later childhood overweight [3]. Several studies have attempted to determine during what time period in infancy or childhood RWG predicts later adiposity but have come to mixed results [6, 7] although, early infancy has been suggested as a critical period [5].

Observed risk factors for rapid weight gain operates both before and during pregnancy as well as early in life. These include maternal pre-pregnancy overweight [8‐12] and excessive maternal gestational weight gain [9‐11], maternal and paternal overweight [8], maternal smoking during pregnancy [8, 13], maternal smoking after birth or history of smoking [13], smoking in the same room as the child [8], male sex in the child [13, 14], younger gestational age, first born status [13] and low socioeconomic status [15]. Besides these risk factors, a number of nutrition- or feeding practice-related factors acting early in life have been associated with RWG [16‐18]. Breastfed infants have a slower weight gain trajectory compared to infants fed on formula milk, at least in Westernized settings [17]. The milk type (i.e., formula milk versus breast milk), and mode of feeding (i.e., directly from the breast versus from a bottle), both independently and in combination with each other may be of importance regarding associations between early feeding and RWG [18, 19]. Infants fed on formula milk have been shown to have higher intakes of protein and energy and a faster weight gain than infants fed on breast milk [19], and formula milk with a high protein content promotes RWG [20]. In terms of mode of feeding, bottle-feeding has been associated with RWG regardless of whether the bottle contained formula milk or expressed breast milk [18].

In the Swedish context, milk cereal drink (MCD) (“gruel”) which is a liquid-based complement to breast milk recommended from the age of 6 months [21‐23], is also a factor that may have an impact on RWG. MCD is commercially available as a ready mix [24]. It is made from grains and dehydrated skimmed milk, mixed with hot water. The most common grains in gruel are oats but versions with wheat, rye, semolina and corn are also available. It contains approximately 65 kcals/100 mL, 2.7 g protein, 8.3 g carbohydrates and 2.1 g fat [23]. Positive associations between MCD consumption and overweight have been found [21, 22, 24].

The early establishment of excess weight demands interventions already in infants and toddlers [25]. Changing modifiable risk factors early in life may be an effective way of reducing the prevalence of overweight in children [25, 26]. Early nutrition and feeding practices have been identified as modifiable risk factors for overweight and obesity [25], but in order to develop early interventions, more research is needed regarding current dietary practices and RWG in infants [4, 27].

The aim of the present study was to examine nutrition- and feeding practice-related risk factors for RWG during the first 0–3-4 months, 0–6 months and 6–12 months of the first year, adjusted for biological (birth weight and sex), socioeconomic and parental health-related risk factors for RWG or childhood overweight or obesity.

In this longitudinal birth cohort study, positive associations between nutrition- and feeding practice-related risk factors and RWG during the first year were found.

During the first 0–3-4 months, 47% of the infants experienced RWG and during 0–6 months the corresponding number was 46%. Not so many studies have examined weight gain during the first six months of life, but in one study with Japanese children, born between 1988 and 2000, 22.7% had RWG between 0 and 3–4 months [32]. In a Brazilian study with children born during 1993–1994 the percentage of children experiencing RWG between 0 and 6 months was 41,9% [33]. In a Swedish study with children born 1984–1985 and an Australian study with children born between 1981 and 1984 the percentages were 25,4% [34] and nearly 22% respectively [35]. One possible explanation for the lower numbers in the studies from the eighties is that not so many children had overweight or obesity back then. However, our results have to be compared with studies of children born in Sweden and other countries during the same time period to confirm if our results are representative for the population and the time period. During 6–12 months, only 8% of the infants in this study experienced RWG. Although the most important period for RWG regarding the prediction of later overweight is unclear, RWG during the first 6 months has been associated with overweight or obesity later in life in earlier studies [33‐36]. The first 6 months of infancy has been shown to coincide with a gain in fat mass rather than in lean mass [37], and RWG during a period with fat mass accumulation may be one explanation for the association between RWG and later overweight.

With the relatively large number of breastfed infants in this child cohort and earlier published research showing slower weight gain trajectories in breastfed infants compared to infants fed on formula [17], the number of infants experiencing RWG during 0–3-4 and 0–6 months may seem unexpectedly high. However, at birth, 24% of the infants were bottle-fed, and at 3–4 months and 6 months the corresponding numbers were 46% and 76% respectively. Bottle-feeding at 0–1, 3–4 as well as at 6 months remained as a risk factor for RWG during the first 0–3-4 and 0–6 months even after adjustment for other risk factors. The same association was found regarding bottle- feeding at 3–4 months and RWG during 6–12 months. Bottle-feeding has been positively associated with RWG in other studies as well [18, 31], and this regardless of whether the bottle contained expressed breast milk or formula milk [18]. Bottle-feeding has been suggested to give more control to the caregiver and to facilitate a more pressuring, non-responsive feeding style [38, 39], and this may be one explanation for the associations found. It has been shown that when formula milk-feeding mothers used bottles without visual or weight cues of the volume left in the bottle, their responsiveness to their infant’s cues increased [39]. Breastfeeding has been suggested to support the development of responsive feeding, and the hypothesis behind this association is that the mother cannot measure how much milk the infant consumes, and therefore has to trust the infant’s hunger and satiety cues [40]. This may be one explanation to the negative association between breastfeeding and RWG that we found in our study. Responsive feeding has shown promising results regarding a reduced risk of RWG and adiposity in early childhood, although the best way to promote responsive feeding and the reasons behind suggested associations between breastfeeding and maternal responsiveness need to be further investigated [40, 41]. Other reasons for associations between bottle-feeding and RWG that have been suggested are a large bottle size [31, 42], feeding on a schedule [14], as well as infant initiated bottle emptying [31, 43]. There is still no consensus regarding the best feeding practice from a bottle in order to avoid RWG and more research regarding this topic is needed.

Another possible explanation for the association between bottle-feeding and RWG found may be the content of the bottle and the relatively high intake of protein associated with formula milk [19]. Newer formula milk products with a lower and better protein quality have been developed [20], but they still contain a higher protein quantity than does breast milk.

Nighttime meals containing formula milk were positively associated with RWG during the first 0–3-4 and 0–6 months while breastmilk given at night were negatively associated with RWG. Besides risk factors associated with bottle-feeding, earlier research has shown that nighttime feeding was associated with shorter sleep duration and increased energy intake, and both factors may lead to overweight later in life [44, 45]. It has been suggested that nighttime milk may be beneficial in breastfed children but should cease after weaning [44, 46]. If nighttime feeding with formula and the associated RWG seen in our study is associated with later overweight as well and if breastmilk given at night may protect against this development need further investigation.

We also found that breastfeeding at 3–4 months was negatively associated with RWG between 0 and 3-4 months and breastfeeding at both 3–4 and 6 months were negatively associated with RWG between 0 and 6 months. This is in line with other studies from high-income countries that have shown that breastfed children have a slower weight gain trajectory than formula-fed children [17, 19]. Breastfeeding has as mentioned above, in contrast to bottle-feeding been suggested to support responsive feeding [40]. Whether the slower weight gain seen in breastfed children protects against later adiposity is debated, there are studies both in favor of [3, 47], and against that hypothesis [3, 48]. The absence of effect on adiposity which was found in the latter one, a study from Belarus have been suggested as being dependent on the reduced number of bacterial infections to which breastfeeding contributed, suggesting that the protective role of breastfeeding may be more relevant in Westernized settings [49].

Regarding the biological, socioeconomic and parental health-related risk factors for RWG this study showed that maternal weight before pregnancy, maternal gestational weight gain and paternal weight were positively associated with RWG during the first 0–3-4 months in a model adjusted for birth weight and sex. Maternal weight before pregnancy and paternal weight were risk factors for RWG during the period 0–6 months as well. Paternal BMI but not maternal BMI before pregnancy was associated with RWG during 0–3-4 and 0–6 months in this study. There are several studies that have shown associations between maternal overweight or maternal gestational weight gain [3, 8]. The importance of paternal factors for offspring overweight are still not clear, but studies have shown associations between paternal overweight and RWG [8]. It would be interesting to study in this cohort if the associations between maternal pre-pregnancy weight, gestational weight gain and parental overweight also are associated with overweight or obesity later in life. Also paternal smoking was associated with RWG between 6 and 12 months and can be considered as a socioeconomic factor, although other mechanisms could not be ruled out. Factors associated with low socioeconomic status have been connected to both RWG [15] and overweight or obesity in other studies as well [8], although the impact of paternal socioeconomic status as well as other paternal factors in relation to childhood overweight is still not fully understood [3].

Separate sensitivity analyses including the 902 boys were performed for all analyses included in this study and the main results remained in those analyses with some exceptions (Additional file 1).

A limitation of our study was the lack of more detailed information on different aspects of nutrition and feeding practices, such as volumes, exact nutritional content at every measurement point and exclusive breastfeeding. Another limitation was our exclusion of infants with missing weight data at 0, 3–4, 6 and 12 months or children weighed outside our decided age limits, which could represent a possible bias that could not be controlled for. This was mainly due to only include measurements close to the measurement points and wider limits for this would affect precision. Worth to mention is that the excluded children had a significantly lower birth weight and therefore may have had an impact on the proportion of children with RWG. There was a risk for selection bias, where children from families that chose to not participate may have been the most socially disadvantaged families with the highest frequency of children with overweight and obesity. We know from other studies that such families often decline to take part in these kind of studies [50]. Measurement error, misclassification and error in the transmission of data to the data files, were not expected to be systematic and were therefore not considered to lead to information bias. Regarding recall-bias, the questionnaires were completed at the CHCCs in connection with each of the nine measurement points and recall-bias should therefore not be a great problem. The major strength of our study was the large sample representing two thirds of all births during the study period in this region of Sweden. They were also followed prospectively over time, with a low loss to follow up. The study used standardized measurements and repeated questionnaires, reducing the risk of information bias. Furthermore, the main outcome variables were based on weight measurements carried out by trained child health care nurses strengthening the reliability of the results.

We found that RWG was more common during the first 6 months of life than during the following 6 months. Bottle-feeding and nighttime meals containing formula milk were independent risk factors for RWG during the first 6 months, whereas breastfeeding during the same period was negatively associated with RWG. Our results suggest that preventive interventions against RWG should start early in life and that bottle-feeding as well as nighttime meals, both modifiable risk factors should be addressed. Furthermore, there is a need for more research regarding the best feeding practice from a bottle in order to avoid rapid weight gain.