Eat up!!! Most mothers do not need to change their healthy diet while breastfeeding. However, if you have a family history of allergy, including asthma and atopic dermatitis, you may want to avoid dairy products, as well as any other foods you are allergic/sensitive to while breastfeeding. Be sure to speak with your health care provider about your diet and when making dietary changes, to be sure that all your nutritional needs are being met.
Some babies are indeed sensitive to foods in their mum's diet, but I would caution against arbitrarily limiting your diet unless you have reason to suspect a particular food is bothering your baby. In this case, try eliminating the food, which is the most likely culprit for at least one week. (Remember to read all labels.). If you do not see an improvement, you can add this food back into your diet and try another food to see if it is the offender. Keeping a journal with foods eaten and your baby's behaviour may be helpful.
Dairy products in a mum's diet can sometimes cause sensitivity. (This sensitivity to milk protein is not at all related to lactose intolerance.) Other foods you may consume that your baby may show sensitivity to include eggs, peanuts and other nuts, wheat, soy, corn, tomatoes, onions, cabbage, berries, nuts, spices, pork, seafood, citrus fruits and juice and chocolate.
Basically, while breastfeeding, it is best to eat a nutritious, well-balanced diet: choose foods that are close to their natural state, making sure to include at least five servings of fruits and vegetables each day. Try to go light on processed foods.