I don't see how doing OP would make you gain or lose weight. You are not swallowing the oil and the benefits don't weigh anything. I tend to believe it's just coincidences that correlate but not the OP that has anything to do with gaining or losing weight.
But OP is not a scientific thing, at best all any of us can do is judge by our own individual experience what is happening to us personally. For example, I love to OP but have never seen one iota of change in the color of my teeth. That doesn't mean it doesnt happen to others, it just does not happen to me. So following that theory maybe a body could gain or lose weight??? LOL