I'm surprised to hear people on this list still talking about
foremilk/hindmilk 'imbalance' - the following is an excellent explanation of
what's actually going on, stolen in part from (I think) Sandra Yates:

Undigested lactose in the gut can lead to bloating, pain, gas, flatulence,
pain, and watery, explosive (sometimes green and mucousy) stools.

The biggest factor in digestion of lactose is the level of fat received by
the baby.  Fat levels in any one feeding are largely related to how long
it's been since the last feeding (shorter intervals = higher relative fat
content) and how well a breast is drained ('empty' breast = high fat, full
breast = low fat). 

We don't make two kinds of milk (even though people refer to foremilk and
hindmilk) - as milk is produced in the breast, the fat globules in the milk
tend to stick to each other and to the walls of the alveoli (where the milk
is made).  Between feedings, milk collects in our breasts and gradually
moves out towards the nipple, leaving more and more of the fat "stuck"
further back in the milk ducts.  The more time between feedings, the lower
the fat content of the milk easily available to the baby at the beginning of
the feeding.

Once let down is triggered, milk is squeezed down the ducts until it becomes
accessible to the baby.  Milk production is not faster during let down - the
flow is simply faster.  There are several let downs per feeding, even though
most of us only feel the first one.  (Milk Ejection Reflex/MER)

As the breast starts to empty, the fat globules begin to dislodge and move
down the ducts (let down facilitates this process).  So further into each
feeding, the higher the fat content of the milk, as more and more fat
globules are forced out.  The end result is that milk gradually increases in
fat as the feeding progresses.

Think of each nursing session as being like turning on a faucet.  The first
water you get out of the tap is usually cold.  As the water runs, it
gradually gets warmer and warmer and warmer.  This is what happens with the
fat content in milk, gradually increasing in fat content throughout the
feeding.  

If there is a long period of time before the faucet is used again, then you
go through the cold-to-hot process once more, but if you turn the water on
fairly soon after it was used, the water is either pretty warm or still hot,
depending upon how long it's been since the faucet was last on.

This is how it works with milk as well - the longer the time between
feedings, the lower the fat content at the beginning of the next feeding.
If feedings are closer together, you're starting off with a higher fat
content.

Letting the baby decide when to come off the first breast helps ensure that
each breast is drained as well as possible, and that the baby has received
as much fat as is available from each 'serving'.  In some cases, block
feeding (using only one breast for a period of time, ranging from 3 hours to
12 hours depending on the mom) is needed to slow down milk production.

Ingrid
LLLC Leader, IBCLC

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