LAUSR

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.