Why does whole wheat flour become rancid sooner than white flour?

Whole wheat flour becomes rancid more quickly than white flour because of the presence of the wheat germ.

A wheat kernel consists of three main parts: the starchy endosperm, the outer bran layers, and the oily germ. During the production of white flour, the milling process removes both the bran and the germ, leaving only the endosperm. Because the germ is rich in oils, its inclusion in whole wheat flour—which utilizes the entire kernel—makes the product more susceptible to oxidation and spoilage over time. In contrast, refined white flour preserves longer precisely because these oil-containing components have been removed.123