Extraneous cellulose: Effect on protein utilization.

SINCE THE EARLY work of Rubner, it has been shown
that the digestibility of bread or flour decreases as more
of the bran is included and the cellulose content increases.
It appears likely that the principal controlling
factor affecting the digestibility of high extraction flours
is the cellulose or undigestible residue which they contain.
The actual mechanism which accounts for the
lower digestibility of protein as the fiber content of the
diet is raised is not yet clear.
McCance et al. studied (1) the rate of passage of
brown and white bread through the digestive tract of
man radiologically and found that the brown bread was
evacuated from the stomach and passed through the
small intestine more rapidly than white bread; the residue
from the brown bread, when in the ileum and colon,
appeared to be greater than that from the white bread.
An inverse correlation between the time required for
food to pass through the gut and the digestibility of
protein has been observed.
Recent work carried out in our laboratories revealed
(2) that inclusion of 5 to 20 per cent of extraneous cellulose
in a finely divided form ( > 300 mesh) in a 26
per cent casein diet did not significantly influence the
gastric emptying time in adult albino rats. The present
investigation was carried out to evaluate the effect of
such a cellulose in the diet on the nitrogen utilization
in weanling rats. Investigations were carried out both
under conditions in which the percentages of protein
and of protein calories were kept constant.