From an early lifetime spent while involved heavily with athletics, the hardest part for me growing up in the late `90's and early 2000's, was finding food that wasn't filled with sugar content.
Read the labels before buying in the store! What became my pastime was reading sugar content labels to my mom when we'd go shopping for groceries. I was on a zero-fat, zero-sugar, self-imposed dietary plan for my gymnastics endeavors, but finding food that wasn't full of sugar was basically impossible.
Having done the research, I can tell you that back in the 1970's and early `60's, only during that time was our civilization first introduced to a high-fat diet but few were buying into the concept until the late `70's.
The very first McDonald's restaurant outside the USA, arrived in Canada in 1967 and was not well-received by Canadians. The burgers were full of fat and McDonald's became known as 'poor people food' to those who lived in Canada because the quality was low and so was the cost.
Ever since the `70's however, sugar and fat content have steadily increased tenfold in ALL food, even food that doesn't taste sweet. Right now, I can buy a 5 pound bag of white refined sugar in my supermarket for $1.25 and during the pandemic, it cost .99 cents for 5 pounds of sugar.
Why? Because people were not going outside the house to eat and sugar sales were way down, so the sugar refiners were giving the shitte away at cost!
If you want to maintain a thin lean body, the first thing you have to do is lay off all sugar and fat entirely. Moderate exercise comes second but diet always comes first.