Some lipid hydrolysis products such as medium-chained NEFA (MC-NEFA), sphingosine and monoacylglycerols (MAG) possess antibacterial activity, while others, including oleic acid, are essential for the optimal growth of Lactobacillus species. Thus, changes in the concentrations of NEFA and MAG in the distal ileum and colon can potentially selectively modulate the composition of the gut microbiota, especially in early life when lipid absorption efficacy is reduced. As medium-chained fatty acids are enriched in mothers' milk, such effects may be highly relevant during gut colonisation. In the present study, we examined the effect of selected NEFA, MAG and sphingosine on the composition of faecal microbial communities derived from infants aged 2–5 months during a 24 h anaerobic in vitro fermentation. We tested lipid mixtures in the concentration range of 0–200 μm, either based on MC-NEFA (10 : 0 to 14 : 0 and MAG 12 : 0) or long-chained NEFA (LC-NEFA; 16 : 0 to 18 : 1 and MAG 16 : 0) with and without sphingosine, representing lipid hydrolysis products characteristic for intestinal hydrolysis of breast milk lipids. Ion Torrent sequencing of the bacterial 16S ribosomal RNA gene revealed that the relative abundance of lactic acid-producing genera, including Lactobacillus and Bifidobacterium, was generally increased in the presence of 50 μm or higher concentrations of MC-NEFA. For Bifidobacterium, the same effect was also observed in the presence of a mixture containing LC-NEFA with sphingosine. On the contrary, the relative abundance of Enterobacteriaceae was significantly decreased in the presence of both lipid mixtures. Our findings suggest that the high concentration of medium-chained fatty acids in breast milk might have functional effects on the establishment of the gut microbiota in early life.

Despite the importance of human milk fatty acids for infant growth and development, there are few reports describing infant intakes of individual fatty acids. We have measured volume, fat content and fatty acid composition of milk from each breast at each feed over a 24h period to determine the mean daily amounts of each fatty acid delivered to the infant from breast milk at 1, 2, 4, 6, 9 and 12 months of lactation in five women. Daily (24h) milk production was 336·60 (sem 26·21) and 414·49 (sem 28·39) ml and milk fat content was 36·06 (sem 1·37) and 34·97 (sem 1·50) g/l for left and right breasts respectively over the course of the first year of lactation. Fatty acid composition varied over the course of the day (mean CV 14·3 (sd 7·7) %), but did not follow a circadian rhythm. The proportions (g/100g total fatty acids) of fatty acids differed significantly between mothers (P<0·05) and over the first year of lactation (P<0·05). However, amounts (g) of most fatty acids delivered to the infant over 24h did not differ during the first year of lactation and only the amounts of 18:3n-3, 22:5n-3 and 22:6n-3 delivered differed between mothers (P<0·05). Mean amounts of 18:2n-6, 18:3n-3, 20:4n-6 and 22:6n-3 delivered to the infant per 24h over the first year of lactation were 2·380 (sd 0·980), 0·194 (sd 0·074), 0·093 (sd 0·031) and 0·049 (sd 0·021) g respectively. These results suggest that variation in proportions of fatty acids may not translate to variation in the amount delivered and that milk production and fat content need to be considered.

While a wealth of data on the fatty acid composition of mature human milk has been published, limited information is available on the quantities of individual fatty acids supplied to the suckling infant with maternal milk, through the whole first year of life. Our aim was to qualitatively and quantitatively evaluate the fatty acid composition of human milk from Italian mothers, throughout extended lactation with particular emphasis on the long-chain polyunsaturated fatty acids. We have thus measured the total fat content and the concentrations of major fatty acids by quantitative GLC in pooled breast hindmilk collected from all feedings over 24 h at colostrum, 1, 3, 6, 9 and 12 months in ten mothers recruited after delivery of full-term infants. Total saturated fatty acids progressively increase and total monounsaturated progressively decrease as percentage levels, while among long-chain polyunsaturated fatty acids, percentages of arachidonic acid and docosahexaenoic acid decrease from colostrum up to the third month. Hindmilk total lipids (mg/dl) rise more than twofold up to 3 months, and then remain stable. The amounts (mg/dl) of linoleic acid and α-linolenic acid progressively increase, following the trend of total fat, while arachidonic and docosahexaenoic concentrations (mg/dl) remain stable throughout the whole nursing period. Assessment of the intakes per kg body weight shows different trends for the individual major long-chain polyunsaturated fatty acids supplied to the infant from hindmilk during exclusive breast-feeding (3 months). This information may be useful for the evaluation of infant intakes during extended lactation.