I know the official line is not to have the bars for the first couple of weeks, but I've had one every day from the first day on CD and it hasn't affected my weight loss at all. Guess that might not always apply to everyone so perhaps I was just lucky
To be honest, my CDC didn't actually tell me I shouldn't have them so I only realised when I joined the DH forum - having said that I'm really glad 'cos it made that first week much more bearable for me.