Earlier quoted context omitted.
My mother (1973, Edinburgh) bought "Pure, White, and Deadly," and we all read it. I was ten or so. Yudkin attacked white flour, white (processed) fat, and above all white sugar. It made perfect sense to us all, and cutting back on sugar became a slow, yet consistent part of our lifestyle. We never ate that much anyhow. I stopped eating sugar entirely at 15. I still recall the book's cover. Edit: it took me a lot long…
Sugar does have some nutritional value, and is a hallmark of primate diet. Tobacco is an addictive insecticide that won't even get you high.
I'd describe it as being similar to caffeine, it makes you more alert. Of course there are downsides that everyone knows about.