Eating potatoes could have a beneficial effect on the immune system, says a study conducted by Spanish researchers.

The vegetable is considered to be rich in vitamin C, B-complex vitamins and has good doses of minerals like iron, calcium, manganese, magnesium and phosphorus. It has long been known that potatoes are good for bowel health.

It is believed to be good for the immune system, particularly if eaten cold or in a salad, the researchers write in Chemistry & Industry, a magazine of the Society of Chemical Industry.

The scientists carried out a study where they fed growing pigs large quantities of raw potato starch (RPS) for over 14 weeks and found that they had healthier bowels.

They also found that these pigs had decreased levels of white blood cells - such as leucocytes and lymphocytes in their blood. White blood cells are produced due to inflammation or when a person is ill to fight the disease, reports the science portal EurekAlert.

The general decrease in leucocytes observed by the researchers suggests an overall beneficial effect, according to immunology expert Lena Ohman at the Department of Internal Medicine, Goteborg University, Sweden.

Said Jose Francisco Perez, the lead researcher from the Universitat Autonoma de Barcelona: "The use of raw potato starch in this experiment is designed to simulate the effects of a diet high in resistant starch."

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 per cent of the starch eaten by humans 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).

The decrease in white blood cells observed is therefore interesting, and a diet of resistant starch may be worth trying in IBS patients, an expert said.