If the mother does not drink enough fluid, she will pass small amounts of concentrated urine. The body is amazingly efficient at utilising food, during lactation. So although it is not necessary to eat enough for two, the mother will need some extra amounts of food. However she would have to be extremely deficient in her diet before this would affect the quantity or the quality of her milk - her own body would suffer long before the breast milk was affected. The mother should eat her usual diet, which should be well-balanced, in slightly greater quantities.
Cows milk is an excellent source of calcium, which is an important nutrient.
However, if the mother does not take enough calcium in her diet, her body will suffer, not the breast milk. All things in moderation is a good motto. If a mother thinks a food is causing the baby discomfort, she should watch for a repetition the next couple of times she eats that food - only then could it be blamed for the baby s behaviour. The exception to this is if the mother herself or the father has food allergies or intolerances - particularly cow s milk products. However the advice of a dietitian is recommended.