Do potatoes promote weight gain?

The humble potato is marketed as an inexpensive, fat- and cholesterol-free source of potassium and fibre.

But there's also emerging scientific evidence that potatoes might contribute to weight gain, and not just when they're gobbled up in the form of potato chips and french fries.

Ordinary potatoes eaten in moderation also might be fattening, according to a recent US federally-funded analysis of what sorts of food and habits could lead to weight gain in adults.

Those findings, published last month in the New England Journal of Medicine by a team led by the Harvard School of Public Health, are especially worrisome in Idaho, the US's number one potato-producing state.

Potatoes directly employ an estimated 16,000 people in Idaho alone. As many as 40,000 may be indirectly employed because of spuds, and Idaho Governor Butch Otter fired back at the study accordingly.

"News flash: Regularly eating ANYTHING in an irresponsible way contributes to weight gain and other health concerns!" wrote Otter, a trim, 69-year-old rancher and rodeo competitor, who proudly acknowledged in an opinion piece eating "Idaho's famous potatoes" regularly.

Others have chimed in, including Republican Senator Olympia Snowe of Maine, one of the nation's other potato-growing powerhouses.

"It doesn't take a medical journal to determine that deep-frying anything and piling on an excessive number of toppings with no consideration of portion size will add to a person's caloric intake and result in weight gain over time," she wrote in a letter to The Wall Street Journal.

Researchers' analysis shows that the starch in potatoes is the likely culprit, said the lead researcher on the study, Dariush Mozaffarian, an associate professor in the Department of Epidemiology at the Harvard School of Public Health.

It's wishful thinking to blame the toppings, he said. The analysis showed that eating more of several categories of food - including nuts and yogurt - was associated with relative weight loss. Cheese was not associated with weight gain, he said.

"Overall, physiologically, potatoes, refined grains and sugars are all likely equally detrimental for weight gain," Mozaffarian said. "In other words, calorie for calorie, there is little difference between eating a potato, cornflakes, white bread or a bowl of table sugar."

The determination that some foods may be bad for you is especially distressing to the people who sell potatoes, said Corey Henry, a spokesman for the American Frozen Food Institute in suburban Washington.

"We get into some very murky waters when we begin labelling foods - particularly vegetables - as being good and bad," he said. "In our estimate, there isn't any such thing as a 'bad' vegetable."

There's no question that low-carbohydrate, Atkins-style diets "really did have a serious impact on the potato industry", said Joe Guenthner, an economist at the University of Idaho.

But studies such as the recent Harvard one probably have far less of the sweeping societal impact than that of a fad diet, Guenthner said.

"I don't think this is going to change many eating habits," he said, "because there are a lot of studies about lots of foods and lifestyles ... and I hear people say, 'They're finding something bad about everything'."

Regardless, the industry and growers are worried. Their biggest concern is that the study will be used to develop agriculture policy; already the industry is fighting proposed nutritional guidelines that cut potatoes down to no more than two servings weekly in school breakfasts and lunches.

Mozaffarian said the takeaway message from the study was that potato intake should be moderated.

The analysis drew praise from Kelly Brownell, the director of the Rudd Center for Food Policy and Obesity at Yale University.

"There's no question certain forms of potatoes, like potato chips and french fries, should be eaten in a very limited way," he said. "Eating a baked potato has always been considered a very fine thing to do. Now this study makes us look twice at this."

In Idaho, though, there's no stauncher defender of the potato than the growers themselves. Among them: Mark Coombs of Caldwell, who's been farming corn, wheat and potatoes for 25 years, and who sits on the Idaho Potato Commission, the state's marketing arm. He eats potatoes several times a week - he'll even eat them raw. And he has no intention of stopping.

"Every Sunday, for Sunday dinner," Coombs said. "And I'm slender. I'm not obese."