I have heard that if you are dieting to loose weight, once your body gets used to your diet, it adjusts itself to the calorie intake and you cannot burn anymore. [Your metabolism slows down]

for e.g. If i eat 2000 calories a day and i burn 2000 calories as well. Now if i reduce it to 1500 so it means that i am burning 500 calories extra,

How long does it take for my body metabolism to slow down to 1500 calories a day?
Same with workout as well, If i burn 2500 calories by a particular workout, how long will it take for my metabolism to slow down and reduce the calories i burnt?

Hello! My husband and I are completing our first cycling tour (300 miles in four days) in two months. My question is, what should our diet be like as we prepare? I definitely need to lose weight, about 15-20 lbs. What, and how much, do I need to eat to keep up my energy, while losing the extra weight?

Thanks for your help!