That's the one! I read it years ago, it seems to have been cleaned up a bit but still has the bits in that I remembered so well:
Table 4 also raises the rarely discussed possibility of negative selection bias in estimates of the duration effects of breastfeeding. In this table, we see a shift in demographic composition for the longest durations. Compare, for example, mothers who breastfed longer than 12 months to those who breastfed 9?12 months. They have lower incomes, are less educated, are less likely to be white, and are more likely to be Hispanic, all factors correlated with worse child outcomes
So, the negative indications of EBF are being explained away by the wrong sort of mothers doing it :) . To which one would immediately say "hang on - if you say that, then all you have proven is that high demographic mothers have healthier, smarter kids than lower demographic ones" - ie the parents' genes and wealth predict the child's intelligence and health - which is hardly a revelation, and is BF/FF neutral.
And then this...
However, for 11 of the 15 indicators, the mean difference between breastfed children and others drops as duration increases beyond a year, as if it were harmful to be breastfed longer than a year. This conflicts with the generally held prior that breastfeeding is rarely harmful. One could imagine a causal factor to explain harm from prolonging breastfeeding beyond 12 months, such as increased exposure to environmental toxins in breastmilk
Which is of course a very odd statement, because if there are toxins after 12 months there are for sure going to be toxins before 12 months, especially when milk is the only food the baby is taking in. But explaining inconvenient truths away by a completely unverified and rather unlikely cause is all too common in BF "research", I have found.
And the killer line is this:
However, after taking sibling differences and estimating the within-family model (Table 5, last column), PVT score is the only outcome that remains significantly correlated with the duration of breastfeeding.
That is the actual, scientific, evidence based, conclusion of this report.
And remember, they were testing all sorts of things that BF supposedly helps - like BMI, diabetes, asthma, allergies, educational achievement, parent child bond, parent child interaction etc etc.
Ooops
The ending discussion has a far more positive spin than the report (as that is all most people will ever read), and tries to explain away these inconvenient truths by even more recourse to unlikely causes, but it now says (or at least I don't recall it saying before), that - buried in all the positive waffle of course - "Our results also suggest, however, that many of the other long-term effects of breastfeeding have been overstated"
That's an understatement if ever there was one - they found no causality at all :o