MONDAY, Jan. 5, 2015 (HealthDay News) -- Over time, regularly eating whole wheat bread, oatmeal or other whole grains may add years to your lifespan, a new Harvard-led study concludes.
Whole grains are so healthy that a person's risk of an early death drops with every serving added to a daily diet, according to findings published online Jan. 5 in JAMA Internal Medicine.
"We saw clear evidence that the more whole grain intake, the lower the mortality rate is," said Dr. Qi Sun, an assistant professor of nutrition at the Harvard School of Public Health. "When we looked at risk of death from heart disease, there was an even stronger association."
The researchers estimate that every one-ounce serving of whole grains reduced a person's overall risk of an early death by 5 percent, and their risk of death from heart disease by 9 percent.
However, eating whole grains did not appear to affect a person's risk of death from cancer, the study noted.
Sun's team based the findings on data from two long-term health studies dating back to the mid-1980s involving more than 118,000 nurses and health professionals. In the studies, participants were required to fill out food and diet questionnaires every two to four years, which included questions about their whole grain intake.
Freshly harvested grains such as wheat, barley and oatmeal consist of three parts. An outer shell called the bran protects the seed. The germ is the small embryo inside the seed that could sprout into a new plant. And the endosperm -- by far the largest part of the seed -- is the potential food supply for a new plant started from the germ.
In refining grains to make processed flour, manufacturers typically strip away the bran and the germ -- leaving only the calorie-rich endosperm. But whole grain foods such as oatmeal, popcorn, brown rice and whole wheat bread and cereal contain all three parts of the seed.
Over 26 years, there were about 27,000 deaths among the people participating in the two studies, the researchers said.
However, the investigators found that one-third fewer people died among the group that ate the most whole grains per day, compared with those who ate lowest amount of whole grains.
The study wasn't designed to determine cause-and-effect. However, the health benefits held even after the researchers adjusted for other factors that might affect a person's risk of death, including the person's age and weight, and whether or not they smoked.
Whole grain eaters did "have much healthier habits than non-whole grain eaters, but our model controls for that," Sun noted.
Why might whole grains be so healthy? According to Sun, they are rich in fiber -- mainly from the bran -- and that fiber helps slow digestion and prevents harmful spikes in blood sugar levels. In addition, both the bran and the germ contain a number of important vitamins and minerals, such as vitamin E and magnesium, as well as nutrients such as antioxidants, added Joan Salge Blake, a registered dietitian and a clinical associate professor of nutrition at Boston University.
Without the bran and germ, about 25 percent of a grain's protein is lost, along with at least 17 key nutrients, according to the Whole Grains Council, a nonprofit consumer advocacy group.
Studies also have shown that people feel more full after eating whole grains, "so that could help with our waistlines," said Blake, who also is a spokeswoman for the Academy of Nutrition and Dietetics.
"The consensus thus far is it's probably not one thing, but a number of wonderful things that work together in whole grains synergistically for health benefits," Blake said.
Current U.S. guidelines call for people to get half their daily grains from whole grain sources, which amounts to about three servings, Blake said.
She recommends that people include whole grains in all of their meals, and possibly even in some snacks.
"To get that feeling of satisfaction, it's advantageous if you spread out the whole grains throughout your day," Blake said. "By stretching it out throughout the day you're able to maintain that fiber and satiety, which helps you better manage your weight."
There's more on whole grain foods at the U.S. Department of Agriculture.