Metformin works better when not having to sort out carbs in your meals. More carbs more metformin works less on reducing bgs and suppressing appetite. Too low carb can make loose tummy more possible. Its getting a happy medium. When metformin was tested for release as a good diabetic tablet no excess carbs were in the subjects, nor very low carb either. It was made for not excessive carb eaters.
Is your slimming involving a high carb diet?
Try reducing your carb intake a little to get the best out of metformin?