Sometimes it helps to visualize something rather than just talk about it. Herewith a picture of a 1500 calorie day. Since the average sized person needs around 2000 calories a day to maintain body weight, a week of this 1500 calorie would likely reduce weight by one pound as there are 3500 calories in a pound. This assumes no extra exercise which would also burn calories.
I think it is worth noting that this reduced calorie day still has a good amount of food in it. So, the person undertaking it would not necessarily be undergoing any physical hardship. These are good nutritious foods that provide sustenance, not empty junk calories.