Don't forget your butter, lard, and meat drippings!
Fats like butter, lard, mutton, and the delightfully named "meat drippings" were all considered part of a healthy, balanced diet. Put some meat drippings on your lunch bread and you should be fired up for an afternoon of fairly muscular work!
Fat "serves as body fuel and also improves the flavor and texture of food." It's hard to argue with that. In order to make sure people ate their copious amounts of starches, families were urged to eat a couple ounces of butter per meal, and enjoy cakes and puddings made with hefty scoops of butter.
Now seems like a good time to mention that the average life expectancy in 1917 was 54 years.
Butter wasn't the only recommended fat, it was just the most popular; oil, lard, and other meat fats were considered necessary for a well-balanced diet. Also, anyone who didn't cook with fat was a heartless, selfish jerk who didn't care enough to prepare a delicious meal for their family. "Dishes cooked without a certain amount of fat and meals served without butter or some substitute seem, to most persons, dry and unpalatable," the manual states. Indeed.