The Associations of Maternal Prepregnancy Body Mass Index With Human Milk Fatty Acid and Phospholipid Composition in the Observational Norwegian Human Milk Study.

Background: Human milk fat quality depends on its fatty acid (FA) and phospholipid (PL) composition. There is clear evidence that maternal diet influences human milk FA composition. However, the scientific literature concerning associations between prepregnancy body mass index (pBMI) and milk FA and PL composition remains inconclusive.

Objectives: This observational study aimed to identify the associations between maternal pBMI and the milk FA and choline-containing PL species composition, considering study confounders, including fish intake as a proxy for n3 long-chain polyunsaturated FA (n3-LCPUFA).

Methods: We analyzed total FA and choline-containing PL-classes (lysophosphatidylcholine, phosphatidylcholine, and sphingomyelin) in 628 milk samples from the Norwegian Human Milk Study birth-cohort using gas chromatography and flow-injection mass spectrometry, respectively. Multiple regression analysis assessed the relationship between pBMI and milk lipid metabolites (%FA, %PL) (reported as β = standardized regression coefficient with adjusted P value < 0.0005, B(95% confidence interval [CI]) = unstandardized coefficient with 95% CI).

Results: Maternal pBMI showed significant association (P < 0.0005) with n3-LCPUFA [β = -0.138, B(95% CI) = -0.010 (-0.015, -0.005)], n6/n3LCPUFA ratio [β = 0.170, B(95% CI) = 0.020(0.012, 0.028)], monounsaturated FA [β = 0.207, B(95% CI) = 0.128(0.076, 0.180)], and corresponding PL species [%LysoPC16:1, β = 0.171, B(95% CI) = 0.001(0.001,0.002), %LysoPC18:1, β = 0.155, B(95%CI) = 0.005 (0.002,0.007)] adjusted with the study covariates. The percentages of variance explained by pBMI were 40% for the n6/n3 LCPUFA ratio, 34% for n3-LCPUFA, and 10% for monounsaturated FA. Conversely, analyses revealed no significant associations between pBMI and choline-containing PL classes.

Conclusions: Biological factors likely increased stearoyl-CoA desaturase activity, lower lipoprotein lipase activity, and a compensatory higher contribution of nonesterified FA from adipose tissue in mothers with pBMI ≥30 could potentially lead to the observed outcomes. Metabolic differences regarding BMI variances may influence the FA availability for mammary gland triglyceride and PL synthesis. Therefore, in addition to dietary intake, maintaining a healthy maternal pBMI may improve the nutritional quality of human milk, ultimately supporting infants' development.