Hypergeometric polynomials are optimal

With any integer convex polytope $P\subset\midR^n$ we associate a multivariate hypergeometric polynomial whose set of exponents is $\midZ^{n}\cap P.$ This polynomial is defined uniquely up to a constant multiple and satisfies a holonomic system of partial differential equations of Horn's type. We prove that the zero locus of any such polynomial is optimal in the sense of Forsberg-Passare-Tsikh.