I wouldn't say "sugar" is the cause ... because there are various kinds of sugars. But I do know, from personal experience, that eating a lot of carbohydrates each day does pack on the weight ... including white rice, potatoes, breads etc. Since I had started watching my carb intake due to potential diabetes, my weight does drop when I have low-carb intake days.
It's well known that eating a lot of carbs (ie, bad sugars) actually makes you tired, fatigued, lethargic. And those sugars/carbs turn into fat pretty quickly.
Between all the processed/high carb foods out there ... kids AND adults spending most of their time sitting down (office jobs, school desks, computer games, talking on forums
, etc) ... it's no wonder that a good chunk of America is obese. Kids don't spend hours outside playing like they used to 25+ years ago. I see adults using riding lawnmowers to mow a quarter acre of grass (whereas my hubby uses a push mower to mow nearly an acre each week). Hardly anyone walks to the store or just plain take walks around the neighborhood in the evenings and meet with neighbors. Just about everyone is glued to a TV or computer when not in school or at work.
Yes, I'm guilty of this myself. I do have a slight excuse ... I work from home ... so I'm always on the computer. I do pop up throughout the day to do various household chores. That keeps me from getting too stiff from sitting too long. I can't do much physical activity due to a damaged back and hip.
But when I do significantly reduce my carb intake, the weight does drop. It goes back to the companies packing our foods with unnecessary sugars in order to get us addicted and thus buy more and sooner ... greed. UGH!