Leah and Joe, your questions have a similar trajectory.

(1) The relationship between breastfeeding and intelligence is
controversial.  Maybe there isn't one.
(2)  Maybe the relationship is caused by factors correlated to
breastfeeding but not actually found in the milk itself: parental
educational levels, contact with baby, etc.
(3)  Maybe the way breastmilk causes higher intelligence is the fatty acids
that have now been identified and are being put into formula.

In other words we've moved from "is there really an effect?" to "is the
effect really caused by the milk?" to "can we duplicate it?"

Other Lactnetters have already pointed out that study methodologies,
especially definitions of breastfeeding, differ widely: some are
appropriate, others aren't.  You might want to read Doren Fredrickson's
chapter "Commentary: Breastfeeding Study Design Problems -- Health Policy,
Epidemiologic and Pediatric Perspectives" in _Breastfeeding: Biocultural
Perspectives_, ed. P. Stuart-Macadam and K. Dettwyler.
Michelle Becton gave a reference to the classic study separating the effect
of breastmilk itself from other factors (Lucas et al. 1992): it involved
tube-feeding human milk vs. formula to preemies, and maternal contact and
socioeconomic status were thus eliminated as possible causes.  A good,
brief review of some of the literature and issues surrounding feeding
method and intelligence (as well as other aspects of health) is found in
Allan S. Cunningham's chapter "Breastfeeding: Adaptive Behavior for Child
Health and Longevity", also in _Breastfeeding: Biocultural Perspectives_.

Yes, I believe that there is an effect on intelligence and yes, I believe
at least part of that effect is directly attributable to the milk itself.
Many lactation specialists would not say that breastmilk enhances
intelligence, but rather that formula fails to foster human intelligence as
well as human milk does.

Which brings us to (3): can the effect on IQ be mimicked by adding certain
ingredients to formula?
First of all, as several recent posts have pointed out, the DHA and ARA
added to formula are not identical to those found in breastmilk, having
been derived from non-human sources (to put it mildly), and apparently have
several undesirable side effects.

However, this is just the tip of the iceberg.  In a discussion of
breastfeeding and intelligence, what it really at issue is breastfeeding as
it is perceived and analyzed by modern Western scientific intelligence.
We have a piece-by-piece way of looking at breastfeeding.  It's like the
blind people encountering the elephant: it's a wall!  It's a hose!  It's a
broom!  It's a tree-trunk!  The human brain (even when it was fed
breastmilk :-)  ) is still in the very earliest stages of beginning to
understand the complexities of physiology: it is toddling, but believes
it's off and running, which is dangerous.  We tend to fragment physiology
into little bits that we can grapple with individually, without realizing
how many bits we still don't even see, or understanding how they all fit
together into a dynamic system.

Imagine that you spend a week choosing the most wholesome foods
possible.  It would probably include a wide range of foods, as fresh as
possible: a range of colorful fruits and vegetables, protein in a variety
of forms, different complex carbohydrates.
Breastmilk, believe it or not, is the nutritional equivalent of that
entire, balanced diet of varied foodstuffs -- except that most of the
nutrients in it are also capable of turning into Superman and killing
invading germs at a moment's notice.  Living milk changes from minute to
minute, from hour to hour, from day to day.  It tastes different depending
on what the mother has eaten, and it provides the entire range of nutrients
the baby needs, in the most synergistically effective combinations.
(As you know, the combination of nutrients in a single food, and
appropriate combinations of different foods in a single meal or a single
day, creates a synergy between the nutrients so that their effects are
maximized (for instance, vitamin C enhancing absorption of iron).  On the
other hand, inappropriate combinations can interfere with nutrient absorption.)

Now imagine that a bunch of scientists analyze what you ate that week and
find that there's vitamin C in the grapefruit, lycopene in the tomatoes,
calcium in the molasses, and folic acid in the broccoli.  You spend the
next 6 months drinking diet-plan shakes and eating vitamin and mineral
pills.  My point is not that this is less fun than the first week was, but
that it isn't going to come anywhere near being such complete
nutrition.  It's not that we are still a bit vague on the functions of two
or three or twenty-four of the components of human milk, and we need a
decade or two more to get it just right.  We're as far from being able to
duplicate the *nutritional ingredients alone* in human milk as we are from
being able to deliver the complex nutrition in a week's worth of varied and
healthful eating by making up some milkshakes and adding a bunch of pills.

I like Judy Ritchie's amazing story about the woman who did fine on a vegan
diet in India, but collapsed with severe B12 deficiency in Seattle --
because cleaned American rice didn't contain quite enough incidental insect
parts to provide B12!  Ornithologists periodically argue about whether
hummingbirds and sapsuckers are eating nectar and sap, or the tiny insects
in the juice.  Well, both, right?  Why try to take it apart and say it is
*really* either one or the other?

Best of luck with your studies.

Elise
LLLL, IBCLC
Bath, New Hampshire

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