I think the only shake that says you can do while BFing is the Xndo range. I went on them to support DH last year. I was only having one shake a day as opposed to his two and having masses of extra calcium serves every day (like 4 extra I think). I did lose weight - about 5 kgs in 5 weeks but my milk dropped massively and DS became very very fussy. So from a personal view i don't reccomend it.

I have had lots of success recently with Calorie King and regular exercise.