But now new data shows that while fiber-rich foods are healthy, there is no evidence to prove they prevent colon cancer, CBS News medical correspondent Elizabeth Kaledin reports.
"We have no diet at the present time that we can categorically say it will prevent cancer," says Dr. Moshe Shike of the Memorial Sloan-Kettering Cancer Center.
The study is significant because it looked at the diets of a huge number of people — 725,628 men and women.
Among them, there were 8,081 cases of colorectal cancer, leading researchers to conclude dietary fiber was not protective.
But besides the numbers, there's a bigger lesson to be learned according to Shike, a gastroenterologist.
He believes Americans are under the illusion that one healthy food or behavior can undo other poor health habits.
Fiber has been on the list of "rescue" foods for a long time, but Shike warns, "There is not one vegetable, there is not one chemical or phytochemical."
"The message is that we need to adopt an overall healthy diet," he says.
Fiber is part of a healthy diet. Guidelines suggest we eat 25 to 30 grams a day. An apple is about 5 grams. A cup of baked beans is 19.
But right now the only thing known to prevent colon cancer is that colonoscopy. And that is the problem because only about 40 percent of Americans get a regular colonoscopy.
If you're 50 or over, the recommendation is that you have one every few years. So, Kaledin concludes, it seems most people think eating a big bowl of cereal is a lot easier and just as healthy — they would be wrong about that.