It has long been known that eating potatoes is good for bowel health, but new research suggests that they may also have a beneficial effect on the whole immune system. Especially if eaten cold or in a potato salad, Anne Pichon reports in Chemistry&Industry.

Spanish researchers found that growing pigs fed large quantities of raw potato starch (RPS) had a healthier bowel. Not a surprise, but they also found that RPS pigs had decreased levels of white blood cells, such as leucocytes and lymphocytes in their blood. White blood cells are produced as a result of inflammation or disease, generally when the body is challenged.


The general down-regulation of leucocytes observed by the Spanish researchers suggests an overall beneficial effect, a generally more healthy body, according to immunology expert Lena Ohman at the Department of Internal Medicine, Göteborg University, Sweden. A reduction in leucocyte levels of about 15% was observed in the RPS pigs. Lower lymphocyte levels are also indicative of reduced levels of inflammation, but according to Ohman, the observed reduction in both lymphocyte density and lymphocyte apoptosis by the Spanish researchers is surprising.

Pigs were fed RPS over 14 weeks in what is the longest study of it kind on the effect of starch on bowel health (Journal of the Science of Food and Agriculture doi:10.1002/jsfa.2835). Study leader José Francisco Pérez at the Universitat Autònoma de Barcelona, Spain, said: ‘The use of raw potato starch in this experiment is designed to simulate the effects of a diet high in resistant starch’ says Pérez.

Humans do not eat raw potatoes, but they do eat a lot of foods that contain resistant starch, such as cold boiled potatoes, legumes, grains, green bananas, pasta and cereals About 10% of the starch eaten by human is resistant starch - starch that is not digested in the small intestine and so is shunted into the large intestine where it ferments.

Starch consumption is thought to reduce the risk of large bowel cancer and may also have an effect on irritable bowel syndrome (IBS). Ohman’s team previously found that the overall lymphocyte levels do not vary for IBS patients, but that lymphocytes are transferred from the peripheral blood to the gut, which support the hypothesis of IBS being at least partially an inflammatory disorder. She says the decrease in lymphocytes observed by the Spanish is therefore interesting, and a diet of resistant starch may be worth trying in IBS patients.