Its definitely possible. Ive lost 30+kgs whilst breastfeeding. You need to eat healthy, watch your portion sizes, keep well hydrated. Wear a good bra, and exercise after you have breastfed, this helps preventing mastitis, and to be honest its a heap more comfortable. imo I would definitely avoid any fad diets, the shake ones, and any change in diet that is not focused on delivering you healthy, well rounded meals.