Water‐soluble polysaccharide (WSP) of Opuntia humifusa stems was extracted and its biological activities in mice fed with a high‐fat diet (HFD) were investigated. The mice were treated with oral doses of WSP for 4 weeks. Body weight, fat mass, serum lipid, and hormone profiles, gastrointestinal tract changes were evaluated. WSP treatment resulted in a decrease in fat mass and improvement of lipid and hormone profiles associated with HFD consumption. In addition, WSP improved the gastrointestinal health of the mice by increasing ghrelin‐releasing cells and serotonin‐positive cells and boosted immune functions by increasing the expression of CD4+ cells and nitric oxide synthase. Also, WSP treatment reduced gastrointestinal transit time and increased fecal moisture content. These findings suggest that a sufficient intake of WSP from O. humifusa can be beneficial in preventing disorders that are associated with the consumption of HFD including the preservation of gastrointestinal health. Practical applications Opuntia humifusa is a traditional edible plant widely eaten in Asia for its high concentrations of vitamin C, polyphenols, and flavonoids. The research investigated the biological activity of WSP extracted from O. humifusa stems. The data obtained from this study sheds light on the use of plant‐based polysaccharides in nutraceutical industries as potential functional food materials for the prevention of HFD‐related disorders and improvement of gastrointestinal health. The results of this research could serve as a base for further research on this polysaccharide as a source of functional polysaccharides and promotes its usage on a large scale in functional food materials.

The objectives of this study were to investigate the effects of alcohol‐insoluble polysaccharide (AIP) isolated from the fruit and stem of Opuntia humifusa on bone metabolism in ovariectomized (OVX) mice. Female mice 6 weeks of age were assigned to four groups: Sham‐operated (Sham), OVX control, OVX mice fed 5% AIP fruit of an O. humifusa supplemented diet (OVX + Fruit), and OVX mice fed 5% AIP stem of an O. humifusa supplemented diet (OVX + Stem). After eight weeks, the OVX + Fruit group and the OVX + Stem group demonstrated increased trabecular bone volume and bone mineral density, and partially improved bone microstructure of the proximal tibia was evident in OVX mice. The OVX + Fruit group and the OVX + Stem group also presented significant reductions in both bone resorption and bone formation. These results suggest that AIP from O. humifusa has beneficial effects on trabecular bone mass, through improving the structural properties of the tibia in OVX mice. Practical Applications The Opuntia humifusa, which has been traditionally consumed as a value‐added food, has been used to treat diuretic disease, constipation and arthritis. We found the fruit and stem AIP of O. humifusa played beneficial functions such as regulation of bone mineral density and improving cancellous bone, suggesting they could be applied as a functional food material for the prevention of osteoporosis.