Human Milk Macronutrients and Bioactive Molecules and Development of Regional Fat Depots in Western Australian Infants during the First 12 Months of Lactation

Human Milk Macronutrients and Child Growth and Body Composition in the First Two Years: A Systematic Review

Among exclusively breastfed infants, human milk (HM) provides complete nutrition in the first mo of life and remains an important energy source as long as breastfeeding continues. Consisting of digestible carbohydrates, proteins, and amino acids, as well as fats and fatty acids, macronutrients in human milk have been well studied; however, many aspects related to their relationship to growth in early life are still not well understood. We systematically searched Medline, EMBASE, the Cochrane Library, Scopus, and Web of Science to synthesize evidence published between 1980 and 2022 on HM components and anthropometry through 2 y of age among term-born healthy infants. From 9992 abstracts screened, 57 articles reporting observations from 5979 dyads were included and categorized based on their reporting of HM macronutrients and infant growth. There was substantial heterogeneity in anthropometric outcome measurement, milk collection timelines, and HM sampling strategies; thus, meta-analysis was not possible. In general, digestible carbohydrates were positively associated with infant weight outcomes. Protein was positively associated with infant length, but no associations were reported for infant weight. Finally, HM fat was not consistently associated with any infant growth metrics, though various associations were reported in single studies. Fatty acid intakes were generally positively associated with head circumference, except for docosahexaenoic acid. Our synthesis of the literature was limited by differences in milk collection strategies, heterogeneity in anthropometric outcomes and analytical methodologies, and by insufficient reporting of results. Moving forward, HM researchers should accurately record and account for breastfeeding exclusivity, use consistent sampling protocols that account for the temporal variation in HM macronutrients, and use reliable, sensitive, and accurate techniques for HM macronutrient analysis.

Relationships between the Intakes of Human Milk Components and Body Composition of Breastfed Infants: A Systematic Review

Human milk provides all of the elements necessary for infant growth and development. Previous studies have reported associations between breastfeeding and a reduced risk of developing obesity and late-onset metabolic disorders; however, the underlying mechanisms are poorly understood. Recently, intakes of human milk components have been associated with infant body composition, which is likely partially implicated in the reduced risk of developing childhood obesity among breastfed infants. In this systematic review, we searched electronic bibliographic databases for studies that explored relationships between the 24 h intakes of human milk macronutrients and bioactive components and infant body composition and/or growth parameters. Of 13 eligible studies, 10 assessed relationships of infant body composition and growth outcomes with human milk macronutrients, while 8 studies assessed relationships with human milk bioactive components. Significant time-dependent relationships with infant anthropometrics and body composition were found for intakes and no relationships for concentrations of several human milk components, such as lactose, total protein, and human milk oligosaccharides, suggesting that measuring concentrations of human milk components without quantifying the intake by the infant may provide a limited understanding. Future studies investigating the effect of human milk components on infant growth and body composition outcomes should consider measuring the actual intake of components and employ standardised methods for measuring milk intake.

Maternal high-fat diet decreases milk endocannabinoids with sex-specific changes in the cannabinoid and dopamine signaling and food preference in rat offspring

INTRODUCTION

Maternal high-fat (HF) diet during gestation and lactation programs obesity in rat offspring associated with sex-dependent and tissue-specific changes of the endocannabinoid system (ECS). The ECS activation induces food intake and preference for fat as well as lipogenesis. We hypothesized that maternal HF diet would increase the lipid endocannabinoid levels in breast milk programming cannabinoid and dopamine signaling and food preference in rat offspring.

METHODS

Female Wistar rats were assigned into two experimental groups: control group (C), which received a standard diet (10% fat), or HF group, which received a high-fat diet (29% fat) for 8 weeks before mating and during gestation and lactation. Milk samples were collected to measure endocannabinoids and fatty acids by mass spectrometry. Cannabinoid and dopamine signaling were evaluated in the nucleus accumbens (NAc) of male and female weanling offspring. C and HF offspring received C diet after weaning and food preference was assessed in adolescence.

RESULTS

Maternal HF diet reduced the milk content of anandamide (AEA) (p<0.05) and 2-arachidonoylglycerol (2-AG) (p<0.05). In parallel, maternal HF diet increased adiposity in male (p<0.05) and female offspring (p<0.05) at weaning. Maternal HF diet increased cannabinoid and dopamine signaling in the NAc only in male offspring (p<0.05), which was associated with higher preference for fat in adolescence (p<0.05).

CONCLUSION

Contrary to our hypothesis, maternal HF diet reduced AEA and 2-AG in breast milk. We speculate that decreased endocannabinoid exposure during lactation may induce sex-dependent adaptive changes of the cannabinoid-dopamine crosstalk signaling in the developing NAc, contributing to alterations in neurodevelopment and programming of preference for fat in adolescent male offspring.

Lysozyme Gene Expression in 3T3-L1 Cells Sustains Expression of Adipogenic Genes and Adipocyte Differentiation

Substantial levels of lysozyme in adipose tissue in association to obesity have been recently demonstrated in mice and humans. In addition, experiments in mice suggest that lysozyme might impact on adipose tissue adipogenesis. To further investigate the relationship between lysozyme and adipogenesis, in the present study, we aimed to study lysozyme (Lyz2) during 3T3-L1 adipocyte differentiation and its possible role in adipogenesis. Time course experiment during 3T3-L1 adipocyte differentiation indicated that Lyz2 gene expression decreased at day 4, which was caused by isobutylmethylxanthine administration, and recovered at the end of the process (day 8). Importantly, the impact of isobutylmethylxanthine-induced downregulation of Lyz2 gene expression on adipogenesis was not comparable to that observed in the full cocktail, questioning whether the reduction in lysozyme at early stage of adipocyte differentiation is relevant to this process. In fact, the depletion in Lyz2 expression had a negative impact on adipogenesis, and rosiglitazone administration failed to compensate for the anti-adipogenic effect observed in Lyz2 gene knockdown cells. Otherwise, when Lyz2 gene knockdown cells were co-cultured with control cells, these cells had higher expression of adipogenic genes than those co-cultured with themselves at the end of adipocyte differentiation. In conclusion, this study suggests that lysozyme expression in 3T3-L1 cells sustains expression of adipogenic genes and adipocyte differentiation.