Energy Packed Sunbeam Bread

As you may have noticed, I've been going through a lot of old food and beverage ads recently digging up material for the blog and I've started to notice certain patterns. One is that, from the Thirties to the Fifties, manufacturers frequently promoted the "energy" in their products. This was especially true with candy companies like Curtiss,

but these ads for Sunbeam Bread show that it wasn't limited to sweets.

It would be interesting to know a bit more of the history here, but I have no idea where to look.