Eating potatoes can reduce irritable bowel syndrome and may also lessen the incidence of bowel cancer, writes Dr Marina Murphy
Given that we're "top of the pops", with the largest per capita consumption of potatoes in the world, recent research supporting a protective effect of long-term potato consumption on bowel health is certainly good news.
Spanish researchers have conducted what they say is the longest study yet of the effect of potato starch on bowel health. The results confirm the beneficial effects of fermenting potato starch in the bowel and demonstrate the positive effects of the potato on the bacteria that live in our intestines.
Growing pigs were fed large amounts of raw potatoes over a period of 14 weeks. Because raw potato starch (RPS) is very resistant to digestion - called resistant starch - it moves from the small intestine into the large intestine to ferment. This fermentation is known to result in increased levels of butyrate, a substance known to protect normal cells but to speed up the destruction of abnormal cells. (Journal of the Science of Food and Agriculture doi:10.1002/jsfa.2835)
However, new and as yet unpublished research reveals a simultaneous reduction in white blood cells, including leukocytes, lymphocytes and neutrophils in the pig's blood. White blood cells are produced in reaction to an assault on the body, and levels increase in response to allergies or infections.
Because the pigs fed RPS had reduced levels of white blood cells, the researchers say this could be an indication that intestinal bacteria are much less aggressive in the presence of resistant starch and so produce less toxins. Less toxins mean less stress on the body, so it does not have to work as hard.
This would be expected to have a beneficial effect in terms of preventing bowel cancer and irritable bowel cancer for example says researcher Jose Francisco Perez at the Universitat Autonoma de Barcelona.
Bowel cancer is one of the deadliest cancers. It kills almost half of those diagnosed with it, because it is usually not diagnosed in time to be treated effectively.
While humans couldn't possibly eat as much resistant starch as these pigs were given, we're streets ahead of other nationalities. We eat 140kg (22 stone) a head per year, far more potatoes than any other country. The French, for example, eat just 40kg a head per year.
Even so, with levels of bowel cancer hovering around the European average in Ireland, it seems that we are not benefiting from our mammoth potato consumption. Perez says this may be because humans tend to eat more fat than pigs and this can affect carbohydrate fermentation.
The fact that we are also one of the largest consumers of milk in the EU and are becoming increasingly obese could explain why we don't seem to be reaping the benefits of our spud addiction.
Although humans do not eat raw potatoes, resistant starch does feature in our diet. About 10 per cent of the potatoes we eat is not digested in the small intestine and so moves into the large intestine where it ferments in the much the same way as RPS. Also cold boiled potatoes and potato salads contain higher levels of resistant starch.
Pigs were used in experiments because it is generally accepted that their anatomies and microflora are the closest to humans'.