you can drink fruit juice before every meal. it has vitamins and all good things but no fats. additionally you wont want to eat too much of other food because you will feel full due to juice. i did this when i wanted to lose weight. and honestly you can eat ten big chunks of watermelon but still you wont gain any weight, there is just water in watermelon... and we cant stay slim for all 12 months in year... there is some season/evolution thing... at best if you succeed to stay slim for 8 months every year then it's huge achievement...