Some sources suggest a breastfeeding mother needs to consume an extra 500 calories a day, but recent studies indicate this recommendation may be a bit too high. The Subcommittee on Nutrition During Lactation (1991) recommends a breastfeeding mom consume about 2700 calories per day. In actuality, most women consume around 2200-2400 calories per day.
Undernourishment of the breastfeeding mom usually does not effect the mother's milk to baby, but can deplete mom's nutritional stores over time. The National Academy of Sciences lists one of its major conclusions: "Women living under a wide variety of circumstances in the U.S. and elsewhere are capable of fully nourishing their infants by breastfeeding them…mothers are able to produce milk of sufficient quantity and quality to support growth and promote the health of infants - even when the mother's supply of nutrients and energy is limited." In fact, only mothers who were chronically and severely malnourished had reduced milk supply.
If a mom is eating poorly, she may feel tired and run down. Encourage her to eat well, both nutritionally and calorically, to increase her energy level. In the U.S., a minimum safe intake of 1800 calories per day is allowed, with strong consideration of foods high in nutritional value. With this lower calorie intake, a multivitamin and mineral supplement should be included.
Some low-income moms are discouraged from breastfeeding by health professionals who question whether their diets can sustain themselves and their babies. However, if a mom is malnourished to the extent that it affects her milk supply, it is much less expensive to feed the mom nutritious food than to buy formula for her baby.
Remember: human milk will keep baby healthier and increase his resistance to illness throughout the course of his lifetime!