Infants are likely to develop rapid weight gain and obesity due to physiologic fat accumulation, changes in feeding patterns and eating habits [1]. Thus, infancy is considered a critical period for obesity prevention in children [2]. According to systematic reviews and meta-analysis, excessive weight gain in infancy is significantly associated with subsequent childhood obesity [3]. In addition, excessive weight gain of infants results from excessive energy intake and nutritional status [2]. In these contexts, the association between maternal feeding practices and excessive weight gain of infants needs to be investigated for development of interventional programs to prevent excessive weight gain in infants. Furthermore, identification of factors specific to the Korean population that are related to maternal feeding practices associated excessive weight gain in infants is essential because these factors may be different in different races or ethnicities [4]. In this connection, as prevalence of exclusive breastfeeding which providing only breast milk without other liquids including formula was 18.3% at 5~6 months after childbirth in 2016 [5], this low prevalence of exclusive breastfeeding was related with the situation that maternal leave was 12 weeks for working mothers, and breast feeding was not supported at the workplace [6]. Chubby infants were also considered as healthy and well-developed in Korea [7]. In this context, Korean people tend to encourage more eating, despite the infants' satiety cues [7]. Thus, associated factors with excessive weight gain in infants in Korea differ from those in western countries. However, most associated factors have been identified in Western countries [1, 2, 3, 4]. In addition, excessive weight gain in infancy can be a result of different maternal feeding practices such as lack of exclusive breastfeeding [1], regular feeding without reflecting on signs of hunger in infants [1], overfeeding associated with parental behaviors e.g., feeding large amounts of formula [1], and early introduction of solid foods, i.e. before 4~6 months of age [8]. However, the significance of associated factors such as exclusive breastfeeding is not consistent in previous studies [9]. In this connection, Lefebvre and John [9] suggested controlling covariates including prenatal (e.g. body mass index of mothers before pregnancy) and infants' factors (e.g. birth weight) apart from feeding habits of infants to confirm the association between maternal feeding practices and excessive weight gain in infants.

According to a model from developed by Monasta et al. [10], factors associated with excessive weight gain in young children can be categorized as children's factors, parental factors, and environmental factors. In the same vein, according to literature reviews, sex (boys) of infants [11], birth by cesarean section [11] and birth weight >4,000 g [1, 11] as infants' factors were positively associated with excessive weight gain in infants. In addition, maternal factors during the prenatal stage such as maternal pre-pregnancy obesity [1], excessive weight gain during pregnancy [10, 11], smoking during pregnancy [10, 11], depression during pregnancy [11], and gestational diabetes mellitus [11] were positively associated with excessive weight gain in infants. Parental factors also include maternal age at childbirth [10], parental body mass index (BMI) [10], current maternal employment status [10], and maternal educational level [10]. In addition, environmental factors include family history of diabetes mellitus [10] and current socioeconomic status of the family [10]. Thus, this study aimed to identify the significance of association between maternal feeding practices and excessive weight gain in infants after controlling the covariates including maternal factors during the prenatal stage, infants' factors, parental factors, and environmental factors.

This study identified factors associated with excessive weight gain in Korean infants. In this study, more than 7 months of exclusive breastfeeding was associated with reduced likelihood of excessive weight gain in infants. According a systematic review and a meta-analysis, increasing the exclusivity and duration of breastfeeding were strongly associated with reduced likelihood of childhood obesity [20]. In the same vein, children who exclusively breastfed for more than 6 months had a leaner body shape at 5 years of age [21]. Furthermore, Harder [20] proposed a dose-dependent association between longer duration of breastfeeding (up to 9 months) and decreased risk of overweight in children.

According to Bartok and Ventura [22], behavioral and physiological characteristics of breastfeeding had preventative effects on excessive weight gain in infants. Among the behavioral characteristics, breastfeeding encouraged infants' self-regulation of energy intake [22]. Previous studies have reported that infants have the ability to regulate the feeding amount and intervals in response to their nutritional need. However, bottle-feeding mothers tended to better regulate the feeding amount because they could visually assess and monitor it [23]. Consequently, maternal feeding behaviors may lead to overfeeding and restrictive feeding practice by not responding to infants' cues of satiety and hunger [24]. Meanwhile, breastfeeding mothers were more likely to trust their infants' ability to self-regulate and responded to the infants' satiety and hunger cues [24]. Thus, breastfed infants compared to formula-fed infants had a decreased risk for excessive weight gain with lower prevalence of overfeeding due to a sensitive maternal response towards the infants' hunger and satiety cues [25].

On the physiological characteristics, breast milk contains proportionally more lactose for fueling the metabolism of the central nervous system, and specific fats and cholesterol for building the tissues of the central nervous system [26]. In contrast, protein and mineral content is relatively higher in formula milk from cows that experience rapid gains in body size [26]. Thus, the higher protein and mineral content of cow's milk would support rapid development of skeletal and smooth muscles, bones, and connective tissues [26]. In these contexts, the higher protein content in formula is considered a significant component associated with excess physical growth including weight gain in infants [26]. In addition, a higher omega-6/omega-3 ratio in formulas milk than breast milk might stimulate adipocyte growth and differentiation [27]. Meanwhile, breast milk rather than formulas contains many bioactive factors (e.g. immunoglobulins, live cells, enzymes, pituitary hormones) that might control infant metabolism, appetite, caloric intake etc. that induce physiological effects on body fat levels and weight gain patterns [28]. Moreover, breast milk but not formula contains leptin which regulates energy expenditure and the neuroendocrine axes as a satiety factor [29]. Thus, weight gain in exclusively and longer breast fed infants would be less rapid than that in formula fed infants. In most previous studies, exclusive breast feeding and longer duration of breastfeeding was associated with reduced likelihood of overweight in young children [20]. Thus, nurses in communities and clinics should educate on the importance of exclusive breast-feeding for longer durations and develop strategies for encouraging such behavior and practices. In addition, support for exclusive breast-feeding should be provided in various settings (e.g. schools, workplaces, public spaces).

This study had several limitations. First, data from mothers using self-administered questionnaires could compromise the results due to social desirability biases (e.g., breastfeeding, and smoking). Second, this study used a cross-sectional survey design that limits inferences of causality between the independent and dependent variables. Thus, well-organized cohort studies are recommended in future to verify the causality of the effect observed in this study. Third, participants were selected with convenient sampling methods that sample was taken from mothers visited conveniently selected three public centers. Thus, further investigations with the samples collected with random sampling methods are needed to improve generalization of the findings. Finally, only a few factors were included in the covariates for identification of associated factors excessive weight gain in Korean infants. Thus, further studies are suggested with various potential factors associated factors excessive weight gain in Korean infants such as familiar and social factors (e.g. beliefs regarding overweight of young children, cultural value regarding providing high calorie food to children, and perception regarding weight control behaviors according to gender of children proposed by Davison et al. [30]).

In this study, more than 7 months of exclusive breast-feeding was associated with reduced likelihood of excessive weight gain in infants. This result suggests that nurses in communities and clinics should educate on the importance of exclusive breast-feeding for longer durations and develop strategies for encouraging such behavior and practice. In addition, support for exclusive breast-feeding should be provided in various settings.