ANSWER:

Change your intention and make it primarily for the sake of Allah and losing weight is a byproduct of that. 

QUESTION: I plan to fast 9 days of dhulhijjah (IA). My initial intention of fasting is to obtain reward, but I fear my intention has changed in my head & I am now fasting bec I want to lose weight. 1. will I still be rewarded for fasting regardless of intention. 2. if not, then what should I do.