Study found switching to more fibrous fare lowered calorie absorption, boosted metabolism rate
WEDNESDAY, Feb. 8, 2017 (HealthDay News) -- Switching to whole-grain foods might help keep your weight in check as much as a brisk 30-minute daily walk would, a new study suggests.
Whole grains seem to both lower the number of calories your body absorbs during digestion and speed metabolism, explained study author J. Philip Karl. He's a nutrition scientist who did the research while a Ph.D. student in nutrition at Tufts University in Boston.
While other studies have found that people who eat whole grains are slimmer and have lower body fat than those who do not, Karl said it has been hard to separate the effects of whole grains from regular exercise and a healthier diet overall.
So, for the new study, "we strictly controlled diet. We didn't let them lose weight," he said.
The researchers did that by pinpointing the specific caloric needs of each of the 81 men and women, aged 40 to 65, in the study.
For the first two weeks of the study, everyone ate the same types of food and the researchers computed their individual calorie needs to maintain their weights. After that, the researchers randomly assigned people to eat either a whole-grain or refined-grain diet.
The men and women were told to eat only the food provided and to continue their usual physical activity.
Those on the whole-grain diet absorbed fewer calories and had greater fecal output. Their resting metabolic rate (calories burned at rest) was also higher. The fiber content of whole-grain foods, about twice that of refined-grain foods, is believed to play a major role in those results, Karl said.
"The energy deficit in those eating whole grains compared to refined grains would be equivalent to the calories you would burn if you were to walk about a mile [in] about 20 or 30 minutes," he said. But the study did not prove that whole grains cause weight loss.
''We don't know over the long term if it would translate to weight loss," Karl said, but his team suspects it would. "This would translate to about 5 pounds in a year," Karl estimated.
The study is solid, said Connie Diekman, director of university nutrition at Washington University in St. Louis.
"It provides good evidence that consumption of whole grains is an important part of a healthful eating plan," Diekman said. The study documents how whole grains contribute to feelings of fullness and appear to increase metabolism, she added.
"The study was short in duration and somewhat limited in population diversity, but the outcome is a positive nutrition recommendation that anyone could benefit from," she said.
The study was published online Feb. 8 in the American Journal of Clinical Nutrition.
In a related study in the same issue of the journal, the same group of researchers found that people who ate whole grains had modest improvements in healthy gut environment and certain immune responses. Whole-grain intake has also been linked with a reduced risk of heart disease, type 2 diabetes and some cancers, the researchers noted.
When shopping, how do you find whole-grain products?
Look on the label for ''100 percent whole grains," Karl said. "Just because something is made with whole grains doesn't mean there has to be much in there," he explained. "Look to see if the first ingredient is whole grain, and 100 percent."
There may also be a label, issued by the Whole Grains Council, that indicates what percent of whole grain a food contains, he added.
Karl is now a nutrition scientist with the U.S. Army Research Institute of Environmental Medicine.
The current Dietary Guidelines for Americans recommend eating six servings of grains daily, with at least half of those servings being whole grains.
To learn more about whole grains, see U.S. Department of Agriculture.