The Antinutritional Effects of Cell Wall Polysaccharides

Abstract

As we have seen, one of the most consistent effects of increasing the intake of dietary fibre is a rise in the excretion of both wet and dry weight of faeces. This is associated with greater faecal losses of energy, and a consequent reduction in the apparent digestibility of the energy in the diet. (‘Apparent digestibility’ is defined as intake minus faecal excretion, divided by intake. It may be expressed as a percentage or a proportion.) Although some of the increased faecal material consists of undigested cell wall material, this is often accompanied by nitrogenous matter and lipids so that the apparent digestibilities of both protein and fat are reduced. At the levels of dietary fibre consumption that are typical of the UK, such faecal losses are small but statistically significant. The increases in excreted organic matter also contain bacterial debris and this, to a certain extent, makes the exact interpretation of the faecal losses in terms of dietary intakes somewhat difficult. However, one thing that can be said is that any increase in bacterial mass must have occurred at the expense of the host since it is ultimately derived from food materials that have not been absorbed.