The fasting guides and books has always warned people who have /had eating disorders not to fast. No one pregnant, breastfeeding, not an adult, with certain health conditions, on medications and a few other situations are also advised not to fast. I have followed Dr Westman's advice to eat when hungry, but when eating VLC that might be only once a day. The definition of IF is all over the map now, but merely to get away from constant grazing and snacking, the "stoke your metabolism myth" has benefits for reversing insulin resistance.