In a recent systematic review published in the journal Advances in nutrition, Researchers conducted a systematic review to reveal associations between breast milk macronutrients and infant growth. Their study included 57 publications on the topic, comprising 5,976 mother-child dyads. The study results highlight significant heterogeneity between methodologies and anthropometric results across different studies. However, digestible carbohydrates led to increased infant weight, while milk protein components were positively associated with increased infant height. Surprisingly, milk fat was not associated with any growth parameter in any of the research reviewed here.
Goodbye: Breast milk macronutrients, child growth and body composition in the first 2 years: a systematic review. Image credit: HTeam/Shutterstock
Breastmilk
Human breast milk (HM) is considered the best source of nutrients for infants, especially during their first two years of life. The World Health Organization (WHO) recommends exclusive breastfeeding for the first six months, followed by a combination of HM and other nutrient sources for two years or more. HM is a complex nutrient source comprising mainly water (87%) and macronutrients (13%).
Breast milk contains proteins, fats and carbohydrates, the latter of which are a major source of energy for exclusively breastfed babies. Research on MH has identified the benefits of amino acids and fatty acids (FAs), which together form macronutrients essential for infant immunity, ideal metabolic functioning and development.
Although carbohydrates are the second most abundant component of HM (after water), only 4.6-6.0% of these carbohydrates are digestible by infants’ bodies. Interestingly, research has found that maternal diet has little or no impact on the composition and relative abundance of HM components, suggesting that strong purifying selection prevents alterations in its functionality. biological. Despite much research into the individual components of HM (carbohydrates, proteins, and fats), significant confusion exists between successive studies. Furthermore, little effort has been made to consolidate the overall benefits of these components in synergy or to suggest a standardized methodology for conducting and reporting results on the ground.
About the study
The present systematic review aims to synthesize and validate previous literature on associations between MH and infant anthropometry, particularly growth, during the first two years of life. Given the large amount of literature available on HM, this review constitutes the last in a cohort of three systematic reviews evaluating micronutrients, bioactives and macronutrients.
This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Despite the initial intention to incorporate meta-analyses, severe heterogeneity between studies made this impossible. This study therefore also followed the systematic review without meta-analysis (SWiM) guidelines.
The journal publications were collected from four online scientific databases, namely Medline, EMBASE, the Cochrane Library and the Web of Science Core Collection. All databases were searched from inception until March 2020, with follow-up in March 2022. Inclusion criteria included publications published in English and included both observational reports and randomized controlled trials (ECR). Treatments included breastfeeding as an exclusive source of nutrients or in combination with other dietary sources. Outcomes of interest included growth measures, specifically weight, length, body mass index (BMI), and growth velocity.
The quality of included publications was assessed using the Newcastle-Ottawa scale (maximum score = 18), with publications classified as high (score >13), moderate (7-13), or low quality. (<7). Since meta-analyses could not be performed, statistical analyzes included generation of heat maps to visualize and report summary associations according to SWiM guidelines.
Study results
The database search identified 9,992 publications for selection for study inclusion. Screening of titles and abstracts reduced the number to 937 articles, and screening of the full text resulted in a final dataset of 141 publications, of which 57 related to macronutrients and were therefore used in the present study.
The main findings of the study revealed that breast milk does indeed have a profound effect on the growth of its infant. It was found that HM protein positively influences infant length and that carbohydrate concentrations, particularly the digestible portion, are positively associated with increased infant weight. Although some studies have identified positive associations between infant growth and amino acids, these studies have had confounds in study design and these results therefore need to be verified.
Total fat concentration had inverse associations with BMI and weight-for-age Z-score (WAZ) gain and positive associations with body fat and weight gain. However, again, these studies showed suboptimal sampling methodologies, particularly a lack of accounting for variations in HM fat concentrations over the course of a day.
“Our finding of a lack of consistent relationship between infant fat and growth outcomes could be related to a variety of factors. The fat content of HM is highly variable within a food and a food to another during the day. The majority of studies included in the current review used a single milk sampling time, typically capturing milk early in the morning, and many did not account for milk transitions. fat content between the start and end of a feeding. “
Unexpectedly, fructose concentrations had a positive impact on infant growth, weight, fat mass, and lean mass. Previous research has identified HM fructose concentrations as one of the few HM parameters that vary depending on maternal diet. Accordingly, high-sugar maternal diets may be prescribed to breastfeeding mothers in the future as an important area of intervention.
Conclusions
Although macronutrients are arguably the most studied components of HM, a large majority of the literature presents suboptimal sampling and analysis methodologies, making their results unreliable subject to future research. It is encouraging that the increased accessibility of the HM analyzer allows current and future studies to follow consistent analytical techniques, thereby improving sampling optimality and allowing results to be compared between studies.
The present systematic review aimed to investigate the associations between breast milk and infant growth and found that HM carbohydrates and proteins influenced infant weight and length, respectively. Fat, although showing positive associations with infant growth, needs to be checked further before results can be reliable.
“Synthesis of the literature has been limited by methodological issues related to milk collection strategies and insufficient reporting of results. In the future, researchers should consider using existing validated HM analysis techniques rather than HM analyzers to assess macronutrient content and develop sampling protocols that reflect the temporal variation of HM macronutrients, particularly fat content. Additionally, increased emphasis should be placed on the study of HM as a biological system that functions within the broader mother-infant biological context rather than examining individual components of HM in isolation.
