The transit time of chyme through the gastrointestinal tract is a function of the health of the colon. Shorter transit times are associated with improved gastrointestinal health. The main defining variable of colonic transit time, and therefore colonic health is the dietary fibre content. As the fibre content increases colonic transit time decreases, and stool weight and frequency of defecation increases. For example, in one study1, researchers used a radiolabelled pellet to measure the transit time of food through the gastrointestinal tracts of healthy human volunteers. The key defining variable for the total transit time was the amount of dietary fibre. In this regard high cellulose diets significantly decreased transit time compared to low cellulose diets. Good correlations between the stool weight and dietary fibre with transit time were found, with the weight of the stool explaining around 50 % of the variable in transit time. Defecation frequency also predicted the transit time of chyme through the gut, as would be expected.
These results suggest that gastrointestinal transit times can be accurately predicted from the weight of the stool and the dietary fibre content of the diet. As the fibre content to a large extent determines the stool weight, dietary fibre intake is a good predictor of gastrointestinal transit time, and therefore colon health. Decreasing the transit time of the chyme through the gut is thought to be beneficial because it decreases the duration of time that carcinogens are in contact with the epithelial cells of the gut and therefore limits any possible damage. Western diets with their low content of fibre increase the risk of cancer of the colon significantly possibly for this reason. In addition, dietary fibre has a number of health benefits including the maintenance of correct plasma glucose levels, and therefore the transit time to some extent might simply be a reflection of the other health effects of fibre. The Western diet is known to increase the risk of obesity and type 2 diabetes, possibly due to its detrimental glycaemic effects.
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