We all should know that salvation and God's blessing are by grace. Unmerited favor. We also know that many of God's blessings are, in fact, conditional. If I do this, He will do that. But of course, it's never really tit-for-tat with God. We don't, can't, force Him to bless us just because we did something.
Weight loss is very interesting because it hasn't been as "scientific" as I thought it would be. I thought "I will just eat this many fewer calories and workout and burn so many calories and I will lost this many pounds." Some days I do that, and don't drop an ounce. Somedays I lose more that I thought I deserved to. I like to think that this is weight loss by grace. I set my heart and mind on pleasing God with my actions, regardless of weight loss, and then let Him decide what to do with my body. That way, it's all for His glory. My motivation is from Him and my results are all for His glory.