That’s the shortest answer.
If you want the whole story read “Why We Get Fat,” by Gary Taubes. It’s the more accessible follow up book to his widely acclaimed “Good Calories, Bad Calories,” which is a good book too, but it’s a slog getting through it because it’s so information dense.
I’m not really stealing his thunder by saying it doesn’t take much easily digested sugar to bump up our insulin which in turn signals our bodies to store more fat.
Nowadays we eat like we’re in (an endless) summer preparing our bodies for a harsh winter (that we actually never encounter). Most of the information Taubes goes over was known and well understood before the seventies came along demonizing fat and embracing carbs. All of which was supposed to make us healthier.
Look around, you don’t need any stats or figures – we’re fatter and unhealthier. That trend started with the shift that really took off in the seventies.
The book explains why obesity isn’t a character flaw, and energy equation imbalance, or a call for more exercise. If “Why We Get Fat” starts to get too detailed for you, just skim over it until you get to a more interesting topic. He’s just backing up his argument and so you won’t be lost if you jump ahead sometimes.
Taubes is the real deal as a science writer with other science related books and articles, he’s a physicist without any fuzzy thinking.
If you’re still eating the standard American diet you should read this book.