You can it may just take longer. Your body burns calories just be being awake, breathing, digesting foods etc and this does not even include exercise. So say your body burns 2000 calories daily (just putting in a number not sure what your number would actually be, this would depend on weight, height, body fat percentage etc). You need an extra deficit of 3500 on top of that to lose a lb. So if you eat 2000 cal per day and burn 2000 cal per day you won't gain or lose. But if you eat 1600 cal per day and burn 2000 cal per day you burn 400 per day. Over time that 400 cal deficit will add up. By adding in exercise you'll speed up weight loss even more. Hope this makes sense to you, I tried to explain best I could.