The Van der Waerden conjecture is a lower estimate of the permanent of a doubly stochastic matrix. In this article in Wikipedia it is stated that Egorychev's proof uses the Alexandrov-Fenchel inequality for mixed volumes of convex bodies. Here is a link to the proof (which is very short). Egorychev himself mentioned the latter inequality but in a less direct way I think.
Where exactly the Alexandrov-Fenchel inequality is used in the proof?
I think what is actually used is Alexandrov's inequality for mixed discriminants of symmetric matrices which Alexandrov invented for one of his proofs of the Alexandrov-Fenchel inequality. But the former inequality is easier than and different from the latter.