This topic is covered in an update to the interviews with Ward Nicholson at
http://www.beyondveg.com/nicholson-w/hb/hb-interview1c.shtml.  Here's an
excerpt:

<<Vegetarian philosophy has traditionally relied on observing that the ratio
of intestinal length to body trunk length parallels that of the other
primates as an indication the human diet should also parallel their more
frugivorous/vegetarian diet. However, this observation is based on the
oversimplification that gut length is the relevant factor, when in fact both
cell types and intestinal surface area are the more important operative
factors, the latter of which can vary greatly depending on the density of
villi lining the intestinal walls. In these respects, the human gut shares
characteristics common to both omnivores and carnivores.>>

Cheers,
-- Aaron Wieland