As a young whipper snapper in the 70s and 80s, my free time was mostly spent outside playing football; tennis etc. burning off lots of calories. The amount of time spent in front of a Spectrum/Commodore/MSX was relatively moderate and balanced. I could get away with lots of sugar loaded snacks very easily.
As a 40-something these days, unsurprisingly less of my free time is spent doing such energetic things, with my zimmer frame on order. However, I imagine youngsters of today do far less exercise and proportionally, an awful lot more computer gaming... They simply are not doing enough to burn up the calories, even in these reduced size Mars bars and alike.
If humans are going to "evolve" into spending more of their lives on sofas and at computer desks, diets need to change a lot more than these ~10% weight reductions of chocolate bars!
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