The objective of this study was to examine the relation between the content of pentadecanoic acid C15:0 (PA) and heptadecanoic acid C17:0 (HA) in human milk and the type of the mothers' diet and determine the content of these fatty acids in infant formulas and follow-up formulas available on the market. Thirty-four, healthy mothers, aged 24-33 y were take part in the study. Mothers were classified according to their diet status into one of two groups: diet low in dairy products (15) and standard diet (19). Analyzed 12 differences infant formulas, 6 infant formulas and 6 follow-on formulas. In the group of women whose diet was low in dairy products, the PA content of human milk fat reached on average 0.195 ±0.017% of total fatty acids, and the HA content – 0.202 ±0.012%. In the group of women eating a standard diet, a statistically significant increase was observed in the PA and HA content of milk fat which on average reached: PA – 0.406 ±0.019% and HA – 0.360 ±0.015% of total fatty acids. It was concluded that in respect of human milk, PA and HA could be regarded as biomarkers of milk fat consumption by lactating women. From among 12 investigated infant formulas (IF) and follow-up formulas (FF) which are available in retail, PA of 0.63 to 0.98% and HA of 0.37 to 0.60% of total fatty acids was found in only 4 formulas which contain bovine milk fat. In IFs which, according to the manufacturer's statement, do not contain milk fat, PA content was from 0.04 to 0.07% and HA – from 0.02 to 0.08% of total fatty acids.

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