Pectin is a soluble fibre that is resistant to digestion by human enzymes. Upon consumption pectin forms a viscous gel that may have digestion modifying characteristics. Sources of pectin include fruit but it can be bought in supplemental form from health food shops. Interest in pectin amongst nutritionist centres around the ability of pectin to slow digestive rates and thus moderate glycaemic responses to carbohydrates. This may explain the beneficial health effects associated with fibre and some or all of the disease modifying effects of fruit. The ability of soluble fibre such as pectin to inhibit gastric emptying rates has been measured using scintigraphy. This reduced gastric emptying may decreases the absorption of carbohydrate in the small intestine. Generally the more viscous the product of the fibre the more gastric emptying is delayed and the slower the rate of digestion. Higher quantities of pectin should therefore slow digestion to a greater extent that smaller quantities because they will induce a more viscous milieu in the intestine.
The effects of pectin have been extensively studied in both animal experiments and man. Generally the results show that pectin is beneficial at around 10 grams. For example, one group of researchers1 assessed the impact of pectin on gastrointestinal changes in healthy men. The subjects were fed either 10 or 15 grams of high methoxy apple pectin with a solid-liquid meal. Five grams of pectin fibre was not different to the placebo, but 10 and 15 grams of pectin fibre significantly slowed gastric emptying of water and carbohydrate. Measurements of the plasma levels of gut peptide following the high fibre meals revealed increases in the concentrations of both motilin and gastrin. At 3 hours postprandially, the mean plasma glucose levels of the subjects were higher in the 10 and 15 gram fibre treatments compared to the 5 gram treatment. This suggests that the delayed gastric emptying may produce a situation whereby blood glucose levels are maintained for longer due to slower carbohydrate absorption rates.
These results suggest that addition of 5 gram of pectin from apples to a meal is not able to reduce gastric emptying rate or duodenal carbohydrate absorption. However, higher amount of fibre (10 and 15 grams) are able to delay gastric emptying of soluble carbohydrates. These results are interesting because 10 and 15 grams of fibre may be the level that became unpalatable and may therefore not be physiologically relevant. It is unclear why soluble fibre is able to delay gastric emptying rates, but probably relates to the presence of a physical barrier. This viscous barrier may delay gastric emptying and line the enterocytes of the small intestine delaying the absorption of carbohydrates. In addition, both gastrin and motilin were reduced upon ingestion of 10 and 15 grams of fibre, and these hormones are responsible for increasing the motility of the antrum in the stomach. This may suggest that the viscous fibre increases the resistance of chyme to being emptied from the stomach and this in turn stimulates increases in motility hormones.
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