It is generally felt that going on a major diet during breastfeeding can decrease the amount of much-needed fats in your breast milk. Babies' brains need a lot of good, healthy fats to grow and develop for the first two years of life.
You can diet, but do so responsibly. Cut out as much bad fat as you want, but make sure your diet has plenty of "good" fats. Read more in our section on fatsDo not worry about carbohydrates and protein while you diet. Your milk will have plenty no matter what you eat.
Dr. Bob