In the study, which involved more than 367,000 U.S. adults ages 50 to 71, people were asked how frequently they ate certain foods, including whole-grain bread, cereals and pasta. The participants were then divided into five groups based on how much whole grains they consumed, as well as how much fiber they consumed from grains, known as "cereal fiber."
People in the group that consumed the most whole grains were 17 percent less likely to die over a 14-year period, compared with those who ate the least amount of whole grains.
But the people who consumed the most cereal fiber were 19 percent less likely to die during the study period, compared with those who ate the least cereal fiber.
The results "indicate that intake of whole grains and cereal fiber may reduce the risk of all-cause mortality and death from chronic diseases," the researchers said.
In addition, the findings suggest that "cereal fiber partly accounts for the protective effects of whole grains," they said.
The researchers also looked at people's risk of dying from specific diseases during the study period. They found that those who ate a diet high in whole grains were about half as likely to die from diabetes as those who ate the least amount of whole grains. High consumption of whole grains was also linked with an 11 percent reduced risk of dying from respiratory disease, a 17 percent reduced risk of dying from cardiovascular disease and a 15 percent reduced risk of dying from cancer during the study period.
But after the researchers took into account people's consumption of cereal fiber, they found that these benefits of whole grains were either reduced or went away. In other words, the benefits of whole grains seemed to be due, at least in part, to the cereal fiber within them. [9 Snack Foods: Healthy or Not?]
Grains are seeds that people cultivate to eat, and whole grains contain the entire grain, meaning they include the bran (the tough outer layer), as well as the germ (the part of the seed that would grow into a plant) and the endosperm (which nourishes the seed).
Cereal fibers are found in the bran part of whole grains, so all whole-grain products contain cereal fibers, said study researcher Dr. Lu Qi, an associate professor of medicine at Harvard Medical School. But products with added fiber would not necessarily contain whole grains, Qi said.
Qi said he would recommend eating products high in whole grains or cereal fiber.
The new findings agree with previous research linking consumption of whole grains to a reduced risk of premature death and chronic diseases. A study published last month found that people who ate at least 28 grams of whole grains a day had a reduced risk of death over a 25-year period.
However, the new study cannot prove that eating whole grains or cereal fibers directly contributes to a reduced risk of early death or chronic diseases. Although the study took into account many factors that could affect a person's risk of death and chronic disease, such as physical activity, body mass index and smoking and alcohol consumption, other factors not taken into account by the study might explain the link.
In addition, the study assessed people's eating habits at one point in time, and it's possible that their eating habits could have changed during the study period.
The study is published online today (March 23) in the journal BMC Medicine.
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