Where you get your theory? No overweight citizen because eat bread?

Then it is about diet. Why did you have to mention rice. I can say that rice is better carb source than flour based food or bread in general.

Balance diet will keep you healthy not necessarily fit but not eat more than your body need will keep you fit. Hard labor guys eat more than office guys. So depends.

Just reduce portion. If you get used to eat a lot, then reducing half can make you crazy hungry. However, human body adapts fast. If not how those people that fast can adapt, but do they reduce 5 kg during fasting months? The answer is no. The main reason is body adapts to conserve energy. Well, not because sleep during lunch hour only but human body can reduce metabolism automatically. That is why weight drops when dieting drops fast to certain degree and then slows down. It will take time.

Can ... just reduce rice and eat just lauk