It's sugar and high-glycemic foods. The amount of fructose consumed was too high in 1950 but has skyrocketed since. It's in damn-near everything that's processed, and people suck down fruit juice and sugary drinks like they're dying of thirst. Thing is, what most people think is "thirst" is not - it's sugar craving in liquid form. That's why kids say they're thirsty but won't drink water if offered to them. If one was truly "thirsty" they wouldn't hesitate to drink water.
Not that there aren't other problems with the shit they put in food, but if you're talking about people looking like fat slobs, then certainly fructose consumption is the main culprit.
Yes, cut it out immediately. Limit fructose intake to natural sources, like fruits, and in moderation. Foods that break down into sugars are bad as well. That includes grains and other starchy foods.
Meat. Vegetables. Fruit. Dairy (as close to unprocessed as possible) = real food. It's nice to enjoy a treat once in awhile, but if more than 20% of your meals are shit, you're never going to optimize your health.
The fat slobs, though? They're probably consuming upwards of 150g of sugar daily. You should shoot to keep it under 20g if not lower.