One thing that was eye opening to me was from paying close attention to food labels. I used to try to mostly eat "healthy", so I'd tend to buy the "low calorie" options. What surprised me was how basically they just substitute fat for sugar. Ceasar dressing normal has 1g carbs and 4g fat per Tbsp (45 cal), but low calorie is 4g carbs and 1.5g fat per Tbsp (30 cal). This adds up, and I think I was actually eating a pretty unhealthy balance of macronutrients (fat/protein/carbs) while thinking I was eating healthy, despite my BMI slowly creeping up over a decade to being middle of "overweight" (I'm now in the middle of "normal" range, just from changing my diet).
Well I think treating sugar like smoking is far too extreme, I do think the demonization of fat along with the addition of excess sugar to "healthy" food options is a terrible combination, and that needs to end.