Dietary carotenoids and their modulation of intestinal microbiota

Noncommunicable diseases (NCDs) are a major global health concern, causing 41 million deaths annually. Unhealthy dietary behaviours are closely linked to NCDs, the reason why nutrition and health organizations emphasize the importance of consuming fruits and vegetables regularly. Being the most common lipid-soluble phytochemicals in the human diet, carotenoids and their metabolites have been linked to various health benefits. The effectiveness of carotenoids is influenced by multiple factors, with the intestinal microbiota (IM) playing a pivotal role in their absorption and metabolism. Dietary choices significantly impact the IM composition, affecting microbial species' proliferation, which can have both protective and detrimental effects. Moreover, IM generates metabolites that enter the bloodstream, influencing the host's IM composition and function, and playing roles in certain diseases. The present work aimed to explore the interaction between carotenoids and the IM. An in vitro gastrointestinal digestion simulation was conducted with three carotenoids (β-carotene, lutein, and lycopene), a mixture of these pigments, and the algae Osmundea pinnatifida. After, digested samples were tested on human faeces to assess their impact on gut microbiota dynamics and metabolic activity. At the phylum level, the intestinal microbiota in all tested groups primarily consisted of Bacteroidota, Bacillota, Pseudomonadota, and Actinomycetota, consistent with prior research. In general, carotenoids promoted the growth of Lachnospiraceae family bacteria while reducing Lactobacillus, Enterococcus, Streptococcus, and Bifidobacterium populations. These bacteria used glucose as a carbon source and produced organic acids like succinic, acetic, butyric, propionic, and malic acids. Functionally, all groups exhibited antioxidant and anti-diabetic activity, with lutein and the Mix group showing the highest levels, respectively. None of the samples displayed mutagenicity, and some even exhibited an anti- mutagenic effect. Importantly, all samples with lower carotenoid concentrations were non-cytotoxic. This study reveals the complex relationship between carotenoids and the gut microbiota, underscoring their potential to positively influence human health.