Laxative effect of fibre-rich foods ‘unconvincing’, finds review
Pierre Gélinas from Agriculture and Agri-Food Canada found that despite food industry efforts to create fibre-rich ingredients only two, psyllium and wheat bran, had any real effect.
His review, published in the International Journal of Food Science & Technology, analysed the laxative potential of 50 food ingredients that have been touted to prevent constipation, including pectin (found in fruit and veg) probiotics and sweeteners such as sorbitol.
Fibre-rich relief doubts
“There is a critical need for tailored food ingredients showing true clinical potential for the prevention of constipation,” said the review.
“The evidence that fibre prevents and relieves constipation is unconvincing and uncertain,” it continued.
Nevertheless, the majority of the 10-20% of the global population who seek medical care for constipation try to relieve symptoms with diets rich in fibre, it said.
“…There are major discrepancies between the proposed fibre-enriched ingredients and the consumers’ needs,” said Gélinas.
Faecal weight measure constipation
Faecal weight is used to give the best measure of bowel movements. The desired daily faecal weight is 150g, according to the review.
People with constipation have stools weighing 54-135g per day and usually have fewer than three stools a week.
Most effective ingredients
Psyllium, derived from the plant plantago, was found to be one of the few effective laxatives. Psyllium, 10g, gave a 12.9g increase in faecal weight per day.
However, psyllium has a bland flavour limiting its application in food, said the review. But it has been incorporated into some bread, cakes and breakfast cereals.
Wheat bran was considered to have the best laxative potential among cereals because it is more resistant to fermentation. Although it did not increase faecal weight significantly it does improve the transit time between mouth and anus, another indicator of constipation.
Fruit, veg and cereals
Pectin-rich Fruit and vegetables such as prunes, raisins, pineapple and cabbage contain natural laxatives, but most of this is lost because it is water-soluble fibre that is easily fermented, said the review.
It said that very few breakfast cereals and practically no cereal or granola-based bars would make a substantial contribution to the daily requirements for faecal bulk.
Overeating fibre
According to Gélinas, the impact of laxative-inducing food ingredients may be limited by overeating.
“Fibres are not created equal. Fibre source should be given more importance than fibre intake, beyond a minimal level to be determined. Even if dietary recommendations for fibre intake are met, overeating low-fibre food is a misleading solution for the prevention of constipation and possibly other health problems”
Clinical proofs are needed before considering new food formulations and wheat bran could be used as a bench mark, said the review.
Source:
International Journal of Food Science & Technology
DOI: 10.1111/j.1365-2621.2012.03207.x
‘Preventing constipation: a review of the laxative potential of food ingredients’
Author: Pierre Gélinas
