I don't think I have a heart condition or diabetes, but I could have and I don't know about it, but I have rheumatoid arthritis. And cutting out junk food is helping. I used to drink lots of diet pop, but I've mostly cut that out now and cut right down on sweet food and its definitely helping me. I feel much better.
The reason I see eating sweets as a sin, is because I crave for them. And I believe that anything I crave for is wrong and I am to deny it. I suppose what is a sin to me won't be a sin to someone else as it won't have a hold on them. But if I know it's a sin to me, then it's a sin and I know it's something I have to fight and pray to God to help me to overcome. Although I'm definitely not craving them like I used to do so that's good.
And yes you're right, it's having it in moderation and controlling it. I'll have to try and cut down even more, I think cutting down is one of the best ways if we can't give it up straight away. My husband had a cigarette, then missed one and waited as long as he possibly could, and just cut down taking a bit less all the time until he was down to 3. Now he even hates the smell so there's hope. I truly hope you do it, and me too with the sweets
Maybe we can help each other, even talking helps, I think it helps to strengthen each other when we talk about it and we know that others are going through the same. And we have the greatest help of all our God and father and our lord Jesus Christ and through faith God will give us the strength to overcome. And as James said, resist the devil and he will flee from you. I often think of this when I'm tempted. Good luck and may God be with you.