Hi Anjay, meal replacement diets work by drastically cutting the number of kjs you are consuming. IMO they are not a healthy way to lose weight even if you're not breastfeeding, they usually work in the short term but can create problems in teh long term as your body gets used to starving. If you are breastfeeding, much better to see a dietician or even join somewhere like Weight Watchers or Lite-n-Easy where they will calculate the extra calories you need to be eating while still losing weight at a healthy rate.

Good luck, and enjoy planning your wedding!