Pig out on potatoes this barbecue season - they could help offset some health problems associated with that charred steak, research suggests.
The potato's reputation as a high carb, high GI food has seen it shunned by diet-conscious consumers, especially since the Atkins diet claimed it was okay to enjoy high-protein, high fat foods as long as you laid off carbohydrates.
But research by Plant and Food scientists has vindicated the humble spud as a good source of fibre and resistant starch - compounds which can help to combat the harmful effects of red meat in the large intestine.
New Zealand's high bowel cancer rates are blamed in part on our high red meat diet, linked to the toxic compounds produced when undigested protein is fermented in the colon. A study in which rats were fed a mince and potato-based diet found the fermentable fibre and resistant starch in potato stimulated beneficial bacteria.
"It comes back to the old meat-and-three-vege diet that we were brought up on," says Dr Chrissie Butts of Plant and Food's food evaluation unit. "Our research showed that by delivering dietary constituents that supported beneficial bacteria, restricting the growth of pathogenic bacteria in the large bowel, we were able to have a positive effect on health."
Fibre from fruit and vegetables is known to have beneficial effects on digestion and resistant starch acts in a similar way. But few studies had looked at the combined effects of eating cooked meat with fermentable carbohydrates, says the study published in the Journal of Food Science.
Rats fed a potato fibre diet had lower levels of undesirable bacteria, including bacteroids associated with an increased risk of colon cancer. Potato-resistant starch increased bifidobacteria and lactobacilli, considered to improve gut health.
The rats also had higher concentrations of a group of short chain fatty acids thought to have anti-carcinogenic properties and improve the colon's "barrier" towards pathogens and decrease toxins.
Plant and Food says the research may offer hope to those who love barbecued steak but worry about the effect on their health. It sees potential for processed meats such as sausages to include fermentable dietary fibre.
But the findings should be taken with a grain of salt, says Professor Murray Skeaff of Otago University's human nutrition department.
The findings are consistent with evidence that dietary fibre reduces the risk of colorectal cancers, Skeaff says, but people would need to eat huge amounts of potato to gain the kind of benefits the rats did, he says.
"If you extrapolate the amount of fibre the rats were given to humans, you would need to eat three or four hundred grams of fibre a day - a level no human would ever get to. The recommendation is that we consume 25g of dietary fibre a day and to get there on potatoes alone you'd need to be eating 2kg of potatoes."
Another rider is the way we cook potatoes. Peeling them removes much of the dietary fibre, but cooling cooked potatoes in the fridge increases the amount of resistant starch, making potato salad a potentially healthy accompaniment to barbecued food.By Geoff Cumming Email Geoff