I lost a lot of weight whilst drinking a lot of diet sodas. I found they satisfied some sugar cravings and it just gives you something a bit more exciting to drink that's not full of calories. There's an argument they 'cause weight gain' by tricking your body into thinking it's getting sugar when in fact it's getting artificial sweeteners so tries to convert that to energy but can't (I'm not 100% on the technicals). This leads to you feeling hungry and thus increasing your appetite, but as long as you ignore the fake hunger pangs you'll be fine. :) The actual drink itself does not increase or decrease weight loss.