I'm not sure where I found this information..

Successful breastfeeding has to be worked at and planned for. If the mother wants to be able to provide a bountiful supply of milk, she ought to plan on eating more and sleeping more. She must also cultivate the ability to relax, to leave the household tasks undone, and mentally take a vacation from everyday work while she nurses the baby. The psychological factor can't be minimized; if the woman becomes worried or uptight about anything, it will adversely affect her milk supply. Tension and fatigue are two of the biggest obstacles to having breastfeeding go smoothly.

To avoid these difficulties, one obstetrician tells his patients who plan to breastfeed that they should rest in bed during the first two weeks, except to care for themselves and the baby. Some lactating women need 10+ hours of sleep in order to avoid that tired, "all gone" feeling. Diet for lactation is about the same as when she's pregnant, but she should drink and extra milk and juices. Every time a woman sits down to nurse, drinking something helps to stimulate milk flow.

Many mothers discover that when they are nursing, they can eat twice as much as they normally do, but do not gain weight. Food seems to taste twice as good, too. Be careful about chocolate, cabbage, garlic, onions, and brussel sprouts. Their flavors may get into the milk and upset the baby.