Modulation of miRNAs in Breast Milk via Maternal Diet and Body Composition: a Comprehensive Review

The initial 1000 days of an infant's life represent a critical period for determining their long-term health outcomes. During this time, breast milk serves as the most distinctive and essential source of nutrition for newborns, providing not only the necessary micronutrients and macronutrients but also a range of bioactive components that greatly influence growth and development. Of particular interest are the microRNAs (miRNAs or miRs) present in significant quantities within breast milk. These small noncoding RNAs, ranging from 19 to 24 nucleotides in length, have been shown to play pivotal roles in the regulation of gene expression through intricate cell signaling networks. Key miRNAs frequently detected in breast milk include miR-148a-3p, miR-30a/d-5p, miR-22-3p, miR-146b-5p, miR-200a/c-3p, and let-7-5p, which are implicated in critical processes such as metabolism, immunity, cellular growth, and differentiation. The composition of these molecules in breast milk is influenced by various factors, including maternal diet, genetic predisposition, and environmental exposures. Maternal nutritional habits and body composition before and during pregnancy are particularly important, as they can affect infant health and susceptibility to cardiometabolic diseases. For instance, exposure to an obesogenic environment may alter the phenotype and genotype of offspring, thereby increasing the risk of such diseases. The growing recognition of the importance of the content of miRNAs in breast milk in the context of fetal programming is underscored by mounting evidence that points to the capacity of maternal dietary patterns and body composition to modulate levels of miRNAs and their functional impacts. This review aims to provide a comprehensive summary of the fundamental roles of miRNAs in breast milk and to explore the potential influence of maternal dietary patterns and body composition on their composition and functionality, drawing upon the extant literature in the field.