Usually what's done when a chameleon has MBD is that you give it some liquid calcium sandoz or gluconate every day because it's more easily absorbed than the powders. This helps correct the imbalance along with the exposure to the UVB...but usually continue the regular supplementing with a phosphorous - free calcium powder at most feedings, a phosphorous - free calcium D3 powder twice a month and a vitamin powder with a beta carotene (prOformed) source of vitamin A twice a month and when the calcium is back in balance drop the liquid calcium.
I gutload the insects with a wide assortment of greens such as collards, escarole, endive, dandelion greens, kale, etc and veggies such as carrots, sweet red pepper, squash, zucchini, sweet potato, etc.
Appropriate temperatures as I said before to aid in proper digestion and thus indirectly in the nutrient absorption.
Too much D3 from supplements can build up in the system and push the chameleon towards MBD. An imbalance in the vitamin A and D3 can also led to problems....and even an imbalance in the phosphorous and calcium isn't good. That's why we recommend the supplementing and feeding / gutloading the insects, etc that we do.
Hope that helps!