I love old U.S. government posters:
The "Basic 7" was introduced in 1943. One thing we forget today is that, other then "farm boys" (and not even all of them, particularly from poorer southern / share crop farms) and their families, a lot of Americans were undernourished through the 1930s. Not just in diversity of food, but also raw calories.
While today's challenge for the military is to get most recruits thin enough to serve, the CCC and military in the 1930s struggled to get new members up to weight. Which is one reason why fats and other high-calorie foods were emphasized.
From '56 to '92 we had the "Basic Four / Three square meals a day" plan, then the food pyramid, and just released "My Plate" -- we went from the the mess that was the pyramid's recommendations created by committee...to My Plate which is graphic design by committee.