My faith teaches me that nothing happens without the will of God. And if it brings about good then you can rest assured that it is a blessing from God. It also reminds me that Satan is very aware of human consciousness and our fears. he (Satan) has been around a long time and knows what to whisper to a person to make them doubt a decision that might lead them to glorify God in a way they've never been capable of doing.
Just imagine how wonderful it would be for you to not carry around a ton of weight, how much easier it would be for you to praise and worship God, how grateful of a servant you would become and how high your confidence would soar. Satan knows that if he can keep you in this state of mind in body (spirit) he can keep you away from God.
God creates, man manipulates. If there is a tool out there that can help you reach your weight loss goals you should thank God for His mercy on those of us who thought we were doomed to this unhealthy state of physical self, that He has given us the knowledge to create the tools to cure ourselves.
God bless you and keep you in a positive state of mind! :-D