The Medical Research Council (MRC) published an article today in a journal called Plos ONE that said that breast fed babies are more likely to be irritable at the age of 3 months than their bottle fed counter parts. The paper suggests that mothers perceive the irritability as stress when in fact it is a signal of hunger and entirely normal. The authors say that breast feeding is still much better for babies than bottle feeding and that this study is useful as it prepares mothers for the reality of breastfeeding.
One of the researchers, Dr Ong says (to paraphrase) that bottle fed babies may appear more content, but they may also be over-nourished and gain weight too quickly. He points out that as with adults, feeding is comforting. I think this observation is very interesting, especially as breast fed babies are much less likely to suffer with obesity later in life. It is much easier to overfeed bottle fed babies that breast fed babies for several reasons. Firstly, a breast fed baby has to work quite hard to get the milk. It normally takes at least 20 minutes to breast feed a baby whereas a bottle fed baby can devour a bottle in a couple of minutes.
Another reason is that all babies, whether they are formula fed or breast fed will be irritable at some stage. It can be really difficult to know why they are crying or unsettled. It may be because they are tired, hungry, over stimulated, under stimulated, have wind or a bit of discomfort. How are you supposed to know? If they haven't been fed that long ago, parents may give them some more milk. If they are breast fed, they can only get whatever is in breast (i.e. probably not that much if they weren't fed too long ago.) However, with a bottle fed baby, they can be offered a whole new bottle. And no doubt, whatever the original cause for complaint was, they'll be pacified with more food. Lastly, a bottle fed baby's stomach may stretch due to the amount of liquid that they are given at once. This means that they'll want more next time they're fed.
The authors suggest that the extra irritability may be one of the reasons why mothers give up breast feeding. In the UK, we have really low rates of breast feeding compared to other countries. Many women do try to breast fed, but many give up. According to an article in Pediatrics (1), published in 2008, the most common reason cited was that "milk alone didn't satisfy my baby". The authors of the MRC study suggest that in fact, it may not be that the baby isn't satisfied, but that they are naturally slightly more irritable.
They do also point out that other studies have previously had conflicting results (some noted no difference and some noted that that breastfed babies were less irritable.) Both my babies were exclusively breast fed and I found neither particularly irritable. I also found breast feeding really useful when they were unwell as they found it so comforting. (You can continue to breast feed even if your baby has diarrhoea or vomiting.) There is no doubt that breast feeding can be particularly difficult to begin with (both for the mother and the baby) but once established it is normally hugely satisfying for both.
They say that this is part of an ongoing study so hopefully they'll publish another paper telling us what breast fed babies are like when they are a bit older.
(1) (2008) Why mothers stop breastfeeding: mothers' self-reported reasons for stopping during the first year. Pediatrics 122: Suppl 2S69–76.