One of the wonders of breast milk is that it can meet your baby's nutritional needs even when you're not eating perfectly. (However, if your diet is too low in calories or relies on one food group at the exclusion of others, this could affect the quality and quantity of your milk).
Just because your baby won't be harmed by your occasional dietary lapses doesn't mean that you won't suffer. When you don't get the nutrients you need from your diet, your body draws on its reserves, which can eventually become depleted. Also, you need strength and stamina to meet the physical demands of caring for a new baby.
Many breastfeeding moms feel extra hungry, which makes sense: Your body is working around the clock to make breast milk for your baby. Eating small meals with healthy snacks in between – the way you may have done during pregnancy – is a good way to keep your hunger in check and your energy level high.