The Chinese-born immigrant infant feeding and growth hypothesis
We propose the Chinese-born immigrant infant feeding and growth hypothesis - compared to infants of non-immigrant mothers living in Australia, infants of Chinese-born immigrant mothers will be exposed to less breastfeeding, more infant formula feeding, and earlier introduction of solid foods (all which increase infant protein intake). We further hypothesise that these exposures will increase the risk of: rapid growth in the first year of life, overweight and obesity during infancy and early childhood (Fig. 1). Components of the hypothesis postulated to influence infant feeding and growth are described below.
Ethnicity
Whilst childhood obesity is increasing in all ethnic groups; the prevalence of obesity is higher in non-white populations and influenced by genetics, physiology, culture, socioeconomic status, environment as well as interactions between these variables [16]. Ethnic background has been demonstrated to be an important risk factor for overweight and obesity in Australian primary-school aged children [17–19]. However, there is limited evidence on children with Chinese backgrounds and this needs further investigation.
Cultural factors
Cultural factors such as language, religion, health beliefs, values and behaviours are suggested to influence child and adult obesity [18]. For example, the Chinese cultural belief that a fat baby is a healthy baby [20, 21] may foster feeding practices that promote rapid weight gain and consequently increased risk of childhood overweight and obesity. The cultural practice of grandparents living with and being the key provider of childcare to their grandchildren in China has also been shown to influence the risk of childhood obesity through their attitudes, indulging behaviours and poor health knowledge [22].
Feeding practices, rapid weight gain and risk of overweight and obesity
Breastfeeding
The initiation and maintenance of breastfeeding may explain differential growth trajectories, however the evidence is contradictory. Evidence suggests breastfeeding to be protective against rapid growth [23] and childhood obesity [5, 6], though not all studies have adjusted for confounding factors [24] known to impact child growth (e.g. maternal factors such as socioeconomic status, weight status, smoking, birth weight) [25]. Nevertheless, studies controlling for maternal obesity, smoking and socioeconomic status have still demonstrated significant associations, although the size of the association was reduced [25]. A recent meta-analysis revealed a 10 % reduction in the prevalence of overweight or obesity in children exposed to a longer duration of breastfeeding after adjustment for social factors [26].
The rates of breastfeeding in Chinese living in Australia are unclear. One study reports 6 % of Chinese-Australian mothers to exclusively breastfeed until six months [27], with lower breastfeeding intentions and initiation rates compared to Australian English-speaking mothers [28]. Asian women in Australia have been found to be more likely to be partially breastfeeding (other liquid/solids are given in addition to breastmilk) at six weeks and 12 weeks postpartum compared to non-Asians [29]. Factors suggested to influence breastfeeding practices in Chinese immigrant women include: cultural (spiritual beliefs, the “hot and cold” theory whereby rituals and consumption of particular foods aim to restore balance in the body postpartum), the role of family (spouse, grandparents, particularly the paternal grandmother), Chinese cultural interventions (e.g. language appropriate education) and the surrounding community [30]. There is also a Chinese cultural misconception that Australian infant formula is better-quality than that in China [20].
Formula feeding
High protein formula feeding may contribute to the risk for overweight and obesity [31, 32]. Compared with human breastmilk, infant formula has different macronutrient composition (high energy, high protein, low fat), hormonal and microflora components which may affect infant growth rates, appetite, energy utilisation and eating behaviours [33]. Koletzko et.al proposed the Early Protein Hypothesis - infants with high protein consumption (in metabolic excess) will have early weight gain, adipogenic activity and long-term obesity risk [5, 34]. Accelerated weight gain due to formula feeding in a longitudinal study following Australian infants until 20 years old was suggested to be due to an upward BMI centile crossing on growth charts [23]. Rate of growth is considered important because of associations with later overweight and obesity [2–4].
Feeding practices and introduction of solids
The current recommendation for introduction of solids is at around six months [35]. Whilst not conclusive, emerging evidence from a systematic review suggests very early introduction of complementary foods before four months, may increase the risk of a child being overweight [7]. However this association has not been finitely confirmed due to the complex nature of overweight and obesity, and inconsistencies in capturing and adjusting for confounding variables within individual studies. The timing of introducing solids to infants of immigrant Chinese in Australia is unknown.
Other factors
The importance of confounding factors (i.e. family and socioeconomic variables) [4] which are risk factors for obesity cannot be underestimated. Whilst not central to the hypothesis, factors such as infant birth weight, maternal weight (pre- and post- pregnancy), maternal smoking, parity, age, socio-economic status, income, employment, level of education, family/social support, marital status, need to be controlled for.
Testing the hypothesis – the Chinese-born immigrant infant feeding and growth studies
Study 1 – Infant feeding practices of Chinese-born immigrant mothers living in Australia – a cross-sectional quantitative study utilising the Australian National Infant Feeding Survey
The Australian National Infant Feeding Survey (2010) was a large scale, national survey of infant feeding practices in infants 0–24 months old (n = 28,759) [36]. This de-identified dataset will be analysed to assess potential differences in infant feeding practices between Chinese-born immigrant mothers (n = 602) and a randomly selected subsample of non-immigrant mothers (n = 602) living in Australia. Infant feeding practices that will be analysed include prevalence rates of breastfeeding and infant formula feeding, the age of exposure to other liquids (e.g. water, cow’s milk, toddler milk, soy milk, water-based drinks, fruit juice); and solids. Statistical analysis of this data will include descriptive statistics (means and standard deviations, or proportions; with differences between ethnic groups and infant feeding practices and demographic characteristics determined by Chi-square tests or t-tests as appropriate) and multiple linear regression to examine the influence of ethnicity on the age that liquids and solids were first introduced.
Study 2 – Weight trajectories and infant feeding practices of Chinese-born immigrant mothers living in Australia – a longitudinal quantitative study
The MCH service in Victoria, Australia provides free pre-scheduled appointments from birth until school age [37]. Anthropometric and feeding-related data are collected and enable nurses to track children’s health and growth from birth to school age. A longitudinal analysis (from birth to 3.5 years old) of growth trajectories using a de-identified database from a Local Government Area in Victoria (Australia) with a high proportion of Chinese-born immigrants (7 % of population [38]) will be conducted to examine potential differences in growth trajectories; in addition to breastfeeding, formula feeding and timing of the introduction of solids between infants of Chinese-born immigrants (n = 934) compared with a random subsample of non-immigrants (n = 934). Zscores (bmi-for-age (zbmi), weight-for-age (zwei), length/height-for-age (zlen)) will be calculated using WHO growth standards [39] and rapid weight gain will be defined as an increase (≥0.67) in zbmi from birth to 12 months [40, 41]. Descriptive statistics will be conducted (means and standard deviations, or proportions; with differences between ethnic groups and mean zscores, rapid weight gain and demographic characteristics determined by Chi-square tests or t-tests as appropriate). Growth curve modelling techniques will be conducted to examine the growth trajectories over time.
Study 3 – Qualitative description of feeding practices
The aim of this study is to investigate the Chinese mother’s beliefs, their attitudes to breastfeeding and formula feeding, introduction of solids to gain an understanding of the influencing factors on feeding practices and infant growth. Chinese-born immigrant mothers will be recruited for the study from an area in Melbourne which has a high population of Chinese immigrants. Individual semi-structured interviews (n ~ 36) will be recorded, transcribed and an inductive thematic analysis will be conducted.
Implications of the hypothesis
We propose the Chinese-born infant feeding and growth hypothesis. This study will examine the impact of early feeding practices and identify potentially modifiable risk factors for rapid weight gain and subsequent later risk of overweight. Outcomes from this study will inform future prevention opportunities and allow them to be tailored specifically for the Chinese immigrant subgroup.
