Asparagus is considered a healthy food with a high content of bioactive compounds. In this study, the proximate and mineral composition, non-digestible carbohydrates and bioactive compounds of edible spear, spear by-product and root have been evaluated. Their activity on the growth of human gut-associated bacteria has been studied. The results support the high nutritional and functional value of the asparagus, including its by-products, highlighting the potential of the non-edible parts to be used as prebiotics. A remarkable content in xylose, inulin, flavonoids and saponins has been found. It has been shown that the spear by-product can be selectively used to promote the growth of commensal or probiotic lactobacilli and bifidobacteria strains. It has been confirmed that any part of the asparagus has a potential future as a healthy food or as health-promoting ingredients, however more work is required to identify the compounds able to modulate the human gut microbiota.