There was not such a thing as diet Coke yet. The first evolution of that in my experience was a drink called Tab. It kind of happened along about the same time as cans. The first cans had a seam in them and were pretty heavy affairs. If you decided to crush one against your forehead, it was a real deal. Not like these super light weight cans of today.
Tab was made with saccharine, and it seemed that my parents, who by then were in need of a dieting, actually drank them as a diet type pill. They began buying them in bulk and bringing them home and cooling them in the refrigerator. Seems to me, that is when they really began struggling with weight.
Mom had used saccharine for years in her coffee and tea, and it was a little tiny pill. She would dissolve them in our ice tea before we knew it caused something called cancer in rats. Cancer was a kind of new thing just starting up, so no one was sure why this mattered much. The one thing I remember was that I would rather not drink soda if I had to have a tab. They were just awful tasting to me.