If diet pepsi has no calories and no sugar why is it helpful for losing weight?

Not helpful: I am guessing your question is meant to read why it's not helpful for losing weight, because it causes weight gain. People who drink 12 oz. Diet soda have a 33% increased risk of type 2 diabetes & those who dink 20 oz. Have 66% increased risk! they cause increased Insulin release, slow metabolism & cause cravings for carbs. http://www.huffingtonpost.com/dr-mark-hyman/diet-soda-health_b_2698494.html.