Seaweed polysaccharides and their potential health effects via gut microbiota modulation

Macroalgae, commonly known as seaweeds, are a valuable source of polysaccharides known to modulate gut microbiota. In this work, the impact of polysaccharide structural features on gut microbiota was explored. The low molecular weight algae polysaccharides showed better degradation by gut bacteria. Moreover, the content of sulfate and carboxylic groups seem to promote high fermentation, triggering an increase in gut microbiota health. The effect of ramification degree of algae polysaccharides on fermentability is still unclear. Agar polysaccharides with low molecular weight and a higher degree of sulfation have been shown to produce higher amounts of SCFA, and decrease in Firmicutes/Bacteroidetes ratio. An increase of sulfation degree of porphyran showed to increase the total SCFA production and a decrease on the ratio of butyric to propionic acid. Carrageenan's molecular weight does not seem to affect SCFA production, and the effect of sulfation degree is not clear. The consumption of these polysaccharides was shown to decrease the Firmicutes/Bacteroidetes ratio. Fucoidans of low molecular weight seem to promote a lower Firmicutes/Bacteroidetes ratio. Alginate consumption both of high and low molecular weight has been shown to increase Bacteroidetes. Low molecular weight laminarans are highly fermented and significantly increase the production of SCFA. Ulvan and sulfated rhamnan polysaccharides have been shown to increase the production of SCFA, although microbiota modulation data are still undisclosed. Overall, seaweed polysaccharides have shown several health benefits, which have been related with gut microbiota modulation.