I am sort of following the MB12WBT which allocates 1700 calories for meals and snacks and you are suppose to exercise 6/7 days per week, which I don't. I have lost 4.8kgs and it has not affected my supply. I am still wobbly, particularly around my tummy as I had a c-sect. I am back to me pre pregnancy weight but I'd like to lose more anyway so will continue until I reach goal.
I agree with Sterla, there would have to be a significant drop in calories for milk production to be affected - I think about women in third world countries that have minimal food and can bf.