Walking at a steady state on a treadmill although beneficial would not help much in losing weight since the body learns to adapt to the same effort over a period of time. I would rather suggest that you have short bouts where you increase the intensity of exercise for a given time before returning to normal. Such short bursts of high intensity exercise have proven to be more beneficial for weight loss. Since you are a diabetic and on the insulin pump it is important that you monitor your pre and post exercise blood sugar levels and adjust the rate of infusion accordingly. Make sure you are well hydrated. Give youself enough time to rest. Always have something edible(preferably sugar) within reach in case you start to feel hypoglycaemic. Please consult your health care provider before making any changes to your diet or exercise plan. All the best...