Human Milk Lipid Profiles around the World: A Systematic Review and Meta-Analysis

Abstract

Reported breast milk lipid concentrations may vary with geographical region, postnatal age and year of sample collection. In this review, we summarized data on the concentrations of total fat, total phospholipids, cholesterol and fatty acids in human milk worldwide and their variation according to lactation stage, study area and sample collection year. A systematic literature search was performed using the PubMed, Embase, Web of Science and Medline databases for English language papers and Wanfang and China National Knowledge Infrastructure databases for Chinese language papers. A total of 186 studies evaluating the human milk lipid profiles were included. According to random effects models based on worldwide data, the summarized means (95% confidence intervals) as percentages of total fat were 42.2% (41.1%, 43.3%) for saturated fatty acids (SFAs), 36.6% (35.6%, 37.5%) for monounsaturated fatty acids (MUFAs) and 21.0% (19.3%, 22.7%) for polyunsaturated fatty acids (PUFAs). However, the study heterogeneity was high for most types of fatty acids (I2 > 99%). Human milk from western countries had higher concentrations of MUFAs and 18:1n-9, but lower concentrations of PUFAs, 18:2n-6, 20:4n-6, 18:3n-3, 20:5n-3, 22:6n-3 and total n-6PUFA in compared with those from non-western countries (P: <0.001–0.011). Significant lactation stage differences were observed for total fat and some individual fatty acids. The concentrations of SFAs and 16:0 were significantly negatively correlated with sampling year (P < 0.001–0.028). In contrast, a significant positive correlation between the concentrations of 18:2n-6 and 18:3n-3 and sampling year was observed (P < 0.001–0.035). Our results suggest that the pooling of data on human milk lipid profiles in different studies should be done with caution due to the high between-study heterogeneity. The concentration of lipids, including total fat, cholesterol and specific fatty acids, differs in human milk according to lactation stage, geographical region and year of sample collection.

Human milk nutritional composition across lactational stages in Central Africa

“…In parallel to other cohorts, SFA relative levels were also higher in our cohort and PUFAs, LA, ARA, Omega-3, and ALA were lower, compared to these Chinese women. Indeed, an important recent review including 186 different HM studies showed that HM from Western countries had significantly higher concentrations of MUFAs and lower concentrations of PUFAs, total Omega-6 PUFA, compared with those from non-Western countries ( 89 ). In this review median SFA relative levels are also lower, and median PUFA relative levels were also higher than in our cohort of Central-African women.…”

Evidence on docosahexaenoic acid and arachidonic acid supplementation for preterm infants

“…ARA and DHA are present in human milk, albeit in much lower amounts than their precursors. The wide variation in DHA content is largely due to maternal consumption of seafood [3 ▪ ]. Whether the breast milk of premature babies contains higher levels of DHA is controversial, as a recent study contradicts previous ones [9].…”

“…Other possible outcomes such as retinopathy of prematurity (ROP) and bronchopulmonary dysplasia (BPD) may also be influenced by these fatty acids due to their role as mediators of inflammation and/or oxidative stress [1,2]. However, determining the appropriate intake of LC-PUFA in infants is difficult because the levels of these fatty acids in breast milk vary [3 ▪ ,4 ▪ ,5] and they can also be synthesized endogenously. In preterm infants, this is even more difficult, as requirements are mainly estimated based on the fetal accretion rates, which remain largely uncertain…”

Human Milk Lipids and Small Metabolites: Maternal and Microbial Origins

“…These tri-layer structures deliver triacylglycerols, phospholipids, gangliosides, and many other lipid classes, to the infant [ 13 ]. The lipid portion of human milk is relatively complex, with wide intra- and inter-individual variation [ 14 ]. Although frequently thought to originate directly from maternal diet, the link between human milk lipids and diet is complex, with diet alone unable to account for the entire milk lipidome.…”

“…The purpose of this review is to present the existing evidence on the origins of human milk lipids and small metabolites to inform future research directions and application. A high degree of variability in lipid and small metabolite concentrations has been identified across milk samples from different individuals around the globe [ 14 , 34 ], suggesting that determination of milk composition is complex and dynamic. Human milk lipids and small metabolites may be synthesized locally within the mammary gland (by the mammary cells or the milk microbiota) or they may be incorporated from maternal circulation (originating from the maternal diet, maternal gut microbiota, or other non-mammary tissue) ( Figure 1 ).…”