This cross-sectional study was carried out in Guadalajara, Mexico, during 1998-1999 to identify food taboos among nursing mothers who participated in a breast-feeding support programme. The study included 493 nursing mothers who were interviewed 10-45 days after delivery. A chi-square test was used for finding an association among food taboos, mother's characteristics, and demographic variables. 50.3% of the mothers avoided at least one food in their diet after childbirth due to beliefs that it was harmful during breast-feeding. Forty-seven percent avoided three or more foods. Fruits and vegetables (62%) and legumes (20%) were the most-avoided foods. These food taboos were associated with living more than 10 years in Guadalajara city (odds ratio [OR] 1.95 [1.25-3.09], p = 0.002), breast-feeding experience (OR 1.91 [1.18-3.12], p = 0.005), no-prenatal information about breast-feeding (OR 1.59 [1.08-2.34], (p = 0.01), and other people's suggestion to complement breast-feeding (OR 1.61 [1.09-2.38], p = 0.01). A supportive approach and efficient communication, taking into account mother's characteristics, might reduce the gap between scientific recommendations and nutritional practices of mothers willing to nurse their infants.