Interesting. Few areas have been more afflicted by fads and junk science than diet. I think however the main reason the population is getting fatter is a much more sedentary lifestyle. My family didn’t have a car until I was in the seventh grade. I did an immense amount of walking and biking as I was growing up as a result, and this was quite common. People today spend a huge amount of time sitting in front of a computer screen, as I am doing now. Do a simple test. Keep track of your weight. On days you are working you will probably lose weight during the week. On days you are off you will probably gain weight. Diet control is important, but unless a sufficient level of activity is engaged in, weight will increase gradually, and over time it adds up.
A less salubrious reason for people being thinner, when I grew up, was that most adults, and many teens smoked. That nauseating habit, yes, I have never smoked, is a true appetite suppressant, as I can attest growing up with two parents who smoked. Inhaling second hand smoke would often put me off my feed, and both my parents never gained an excess amount of weight. (I wish I could say the same!) I guess the “coffin nails” did some good after all, unless one remembers the whole cancer thing!