INTRODUCTION
The gastrointestinal tract is a highly complex ecosystem
in which members of the resident microflora
compete for available growth factors." Dietary
modification alters the amount and types of nutrients
present in the gut and would be expected to
alter the growth and composition of the microbial
community. Consistent and reproducible changes in
this bacterial population have, however, been hard
to demonstrate due, in part, to the technical difficulties
associated with identifying and enumerating
highly oxygen-sensitive species of bacteria" and
also the large variations in gut flora between individuals.
l6 Even studies where subjects have engaged
in extreme dietary a l t e r a t i ~ no' ~r c hanged to a fibrefree,
absorbable diet3,' have failed to reveal major
changes in bacterial composition of faeces.
Recently, however, evidence has been accumulating
that the metabolic activity of the gut fiora can be
modified by diet, in particular by those components
that escape digestion by mammalian intestinal
enzymes.