Let f:(ℂn, 0) → (ℂp, 0) be a complete intersection with an isolated singularity at the origin. We give a lower bound for the Milnor number of f in terms of the mixed multiplicities of a set of monomial ideals attached to the Newton polyhedra of the component functions of f. The Milnor number of f equals the bound that we give when f satisfies a condition that we define and that extends the notion of Newton non‐degenerate function studied by Kouchnirenko. Our techniques are based on the notion of integral closure of submodules and its relation with Buchsbaum–Rim multiplicity and mixed multiplicities of a set of ideals.