Just reading my Bounty magazine on the loo (as you do...) and there's a small piece that says...
"Mixed Feeding - if you started off breastfeeding and are now thinking of formula feeding remember that it may be difficult to reverse the decision not to breastfeed. Introducing partial formula feeding with breastfeeding will reduce your milk supply. We also know that mixed feeding can undo some of the protective factors that exclusive breastfeeding can give."
I'm a little confused, and also having a hard time finding more information/research on this. I'm unsure about how formula would prevent the benefits (in terms of antibodies etc) of breastfeeding.