The kitchen is the key

The overt message is to eat less bread.

The covert message is to make sacrifices in order to benefit America during the war. Spend less on yourself, and more money can go towards the war.

It is propaganda because the lady is dressed in red,white, and blue, and the ad is actually going to make you sacrifice. On the surface, however, it is just telling you to eat less bread. The ad wants you to show your support, be patriotic, and give money.