The only way to lose weight is through a calorific deficit. In summary, the deficit is consuming fewer calories than you burn. When this happens, the body will begin to burn its fat as there is no more food left in your body to burn. In general, to lose 1kg of weight, you must reduce the deficit by 1000 calories. So if you were to cut your meal sizes by 500 calories for 20 days, this would lead to approximately a 1kg weight loss. This may not sound like a lot, but remember, weight loss is a marathon and not a sprint. There is no point cutting weight, only to put it back on right away.