CHICAGO (AP) – A new TV commercial shows kids eating hot dogs in a school cafeteria and one little boy's haunting lament: "I was dumbfounded when the doctor told me I have late-stage colon cancer''.

It's a startling revelation in an ad that vilifies one of America's most beloved, if maligned, foods, while stoking fears about a dreaded disease. But the boy doesn't have cancer. Neither do two other kids in the ad who claim to be afflicted.

The commercial's pro-vegetarian sponsors say it's a dramatisation that highlights research linking processed meats, including hot dogs, with higher odds of getting colon cancer. But that connection is based on studies of adults, not children, and the increased risk is slight, even if you ate a hot dog a day. While compelling, it isn't conclusive. So what exactly is the truth about hot dogs?

The 33-second ad launched last month in several US cities provides the perfect opportunity to separate fact from fiction about this mysterious yet so familiar meat. It is to run in September in Chicago and Denver.

The bottom line from several nutritionists familiar with the ad is this: Hot dogs aren't exactly a "health food'', but eating one every now and then probably won't hurt you. "My concern about this campaign is it's giving the indication that the occasional hot dog in the school lunch is going to increase cancer risk," said Colleen Doyle, the American Cancer Society's nutrition director. "An occasional hot dog isn't going to increase that risk."

Americans as a whole eat hot dogs more than occasionally. According to the National Hot Dog & Sausage Council, US consumers spent more than $4 billion on hot dogs and sausages last year. That includes more than 1.5 billion pounds of hot dogs and sausages bought at retail stores alone. The health concerns primarily come from their high fat and salt content and sodium nitrate and nitrite, commonly added preservatives and colour-enhancers. Nitrate-related substances have been reported to cause cancer in animals, but there's no proof they do that in people. Hot dogs typically contain muscle meat trimmings from pork or beef. Contrary to legend, they do not contain animal eyeballs, hooves or genitals, according to the Hot Dog Council's Janet Riley. But the government does allow them to contain pig snouts and stomachs, cow lips and livers, goat gullets and lamb spleens. If they have these byproducts, the label should spell out which ones, a US Department of Agriculture spokeswoman said.

Some also are made with leaner meats, including turkey, as well as tofu or soy protein.

Check the label of a name-brand hot dog, and chances are fat provides around 80 percent of total calories, more than double what's often advised. What's more, saturated fat and trans fat – the fats most strongly linked with artery-clogging – are common ingredients, in some cases providing at least half the fat content.

The hot dog council called the new ad an alarmist scare tactic, but the promoters, a group called The Cancer Project, defend their campaign.

Dr. Neal Barnard, president of the Physicians Committee for Responsible Medicine, called the ad "a way to raise appropriate concern about a deadly concern''. Barnard also heads The Cancer Project, an offshoot of his anti-meat advocacy group.

Hot dogs may be considered as American as apple pie, but Barnard said it's time to change that tradition.

"Children are born with no traditions whatsoever," he said. "You or I might think a hot dog, that just goes with baseball ... We can always change our traditions to be healthful."

The new ad is based on an analysis of five studies in adults by scientists working with cancer research groups not affiliated with Barnard's. Their report last November said eating 50 grams a day of processed meats for several years increases colorectal cancer risk by 21 percent. That equals about one hot dog a day or two deli slices of bologna or five slices of bacon. The duration of daily consumption linked with that higher risk is uncertain. Colorectal cancer was diagnosed between three and 19 years after the studies began, but participants could have been eating processed meats for years before that, said dietitian Karen Collins, nutrition adviser with the American Institute for Cancer Research, a group that analysed the studies.

For a US adult, eating one hot dog daily for several years would increase the average risk of getting colorectal cancer, which is 5.8 percent, to seven percent. On a population level, it would increase the number of people nationwide who get colorectal cancer each year from 58 per 100,000 people to 70 per 100,000, Collins said.