If you are talking about nutrients, there has been some discussion about the value of incrementally increasing the nutrients over the first 72 hour of fermentation along with vigorous aeration.
I tried that with my most recent batch, and have been very pleased with the results so far. I've had very vigorous fermentation from the onset.
If however you are referring to feeding as the process of adding honey or other fermentables to increase the alcohol content, that's a different item altogether.
Say for instance you want to get a super high ABV mead with residual sweetness, you would add honey as the yeast begins to draw near it's tolerance. (KIV-1116 will ferment 20%+) The increase in total volume does briefly lower the ABV, but the fermentation should kick back off and the stronger yeast cells should ferment to a higher ABV.
Oskaar, and others can probably give you a better description of the hows and whys, but this is what I've learned from my first batch of mead.
Check my brewlog
http://www.gotmead.com/smf/index.php/topic,288.0.htm
for the full details on my experience with high gravity and KIV.
lI hope this is at least some of the info you are looking for.
David