This line is often trotted out whenever someone emphasises the economy of breastfeeding over form: 'except that the mother has to consume more food in order to produce adequate breastmilk'. Nonsense.
Firstly, evidence suggests that breastmilk supply is only threatened when the mother's calorie count dips below 1500 a day, which is below the average intake for a breastfeeding woman. More importantly, one of the virtues of breastfeeding is that it can burn 300-500 calories a day. Assuming that the mother doesn't increase her food consumption, and sticks to around a standard 2000 calories a day, this deficit is precisely what's needed in order to maintain a consistent level of weight-loss in the postpartum months. This deficit will allow the body to utilise the fat deposits that were placed down during pregnancy in order to produce breastmilk.
It just really pisses me off when someone makes this argument about how much extra money they spent on food, then says;:"OH, and btw breastfeeding didn't help me lose any weight!' Well, no shit sherlock.
This isn't to say that I think breastfeeding is significantly cheaper (have spent more than I would like to think on a good quality nursing pillow, bras/vests, pump etc), but simply that the argument based on food doesn't compute.