Is there evidence that exclusive breastfeeding gives greater benefits than majority breastfeeding?

[artichokes]

I am considering introducing one formula feed a day once dd2 is 6 weeks. This will ensure that:
(a) I can occassionally go out without dd2 and so do activities with dd1;
(b) dd2 will learn to take a bottle early minimising problems when I have to return to work (with dd1 it was a nightmare as she had only ever known the breast).

These would be too huge benefits for us as a family. I am not worries about endangering supply as I will wait to six weeks and only do one feed a day and anyway my supply is quite amazing at the mo.

So other than the potential for nipple confusion, which I will watch for diligently, is there a downside to one FF a day? For example, is the virgin gut theory credible?

kate, I had a similar thing happen to me and my baby. She was suspected to be IUGR/low birthweight (actually came out 6lb4 - fine) and the SCBU docs insisted on 1oz formula for her first feeds. Her first feed the midwife gave, I don't remember really having a say in that (I had an emergency c-section and looking back was completely out of it really), and then when we put her to the breast she wasn't interested (hardly surprising after having formula!!). Looking back now, I am really angry about it, and when I read things that even a small amount of formula can have an effect I can feel disheartened. After the first day I managed to get agreement from the hospital to breastfeed only - it was a long hard road, latching was difficult, ended up with mastitis twice, but seven months down the line she has not had any more formula and I hope to make it to a year and wean onto cows milk...
Thanks to those who say that exclusive BFing after any formula does help to restore the gut, it does make me feel my efforts were not in vain

Just realised this is quite an old thread! Oh well, felt good to write all that down.