Biobased materials have the potential to be developed into green multifunctional products to replace their chemosynthetic counterparts, which have environmental and economic concerns. However, designing magnetic and porous biomaterials without pore spaces being occupied by exogenous magnets via traditional encapsulation, load, and/or deposition methods remains challenging. This paper describes a novel, facile, top-down strategy of fabricating zerovalent iron particles (Fe0 Ps) embedded into a three-dimensional (3D) zinc-modified starch (Zn-St) framework using the enzymatic reactive extrusion (eREX) method. Raw St underwent Zn-atom fortification, in situ Fe-atom deposition, and micromixing extrusion to produce (Zn-St)10Fe0n (n = 1, 2, 3, 4) extrudates (Es) in a continuous and large-scale mode. A hierarchical porous structure was formed during eREX processing, with mesopores (∼2-4 nm) and macropores (∼50-300 nm and ∼5-100 μm) generated regularly. The (Zn-St)10Fe0n Es were excellent at dye adsorption and magnetic separation, with high levels of St (>70%) as a biodegradable resource. For instance, (Zn-St)10Fe02 Es (St > 83%) removed 61.03 mg/g of methylene blue (∼19 times higher than that of raw St) at 298 K and pH 4.0 via simultaneous physisorption and degradation and were successfully separated due to their saturation magnetization (Ms) value of 25.41 emu/g. The dye adsorption rate and Ms of the (Zn-St)10Fe0n Es can be increased by manipulating the amount of Fe0 Ps. Thus, the novel 3D (Zn-St)10Fe0n Es are promising biomaterials for water purification applications, as well as other food, biological, and environmental fields.