Nonetheless, a recent and highly controlled study in the American Journal of Clinical Nutrition lends support to whole-grain consumption, especially in comparison to refined grains. The conclusions line up with the U.S. Dietary Guidelines 2015-2020, which recommend that carbohydrates make up 45 to 65 percent of a healthy diet, with six ounces from grains. (An ounce of grains is 1 slice of bread, 1 cup of breakfast cereal, or ½ cup of cooked pasta or rice).
The new study, conducted at Tufts University's highly regarded Jean Mayer USDA Human Nutrition Research Center, found that a diet high in whole grains vs. refined grains led to a favorable energy balance. In other words, subjects on a whole-grain diet burned more calories while absorbing fewer. They also showed a trend toward improved glucose tolerance. According to the paper's authors, the results "may help explain epidemiological associations between whole-grain consumption and reduced body weight and adiposity."
Senior author Susan B. Roberts, professor of nutrition and senior scientist at the USDA Nutrition Center at Tufts (and founder of theidiet.com), agrees that many Americans eat too many highly processed and often highly sugared grains. She doesn't, however, find this a good reason to limit whole grains. "I think the anti-carb hype has gone too far for a healthy society," she says. "We should remember that whole grains in the diet are associated with lower cancer rates, so they're good for long-term health."
Her perspective is shared by nutritionist Lauri Wright, who was not part of the Tufts study. "Bottom line, whole grains have many benefits," says Wright, assistant professor in the department of community and family health at the University of South Florida and a spokeswoman for the Academy of Nutrition and Dietetics. "Some didn't appear in this study, because even the refined grain eaters consumed a lot of fiber. Whole grains also increase the antioxidant level of a diet, which is important for health."
Unlike many much-publicized nutrition studies, this one was not designed for calorie restriction or weight loss. Instead, researchers constantly monitored subjects' weights to make sure no one was dropping pounds. With that variable eliminated, they could focus more intently on the whole grains vs. refined grains question at the center of their investigation.
Eighty one subjects were divided into two groups who picked up all their meals each day at the Tufts nutrition center. Subjects had an average age in their mid-50s and an average body mass index of 25.6, slightly above the 25.0 upper limit of healthy BMI, but not overweight or obese. During the six weeks of diet manipulation, all subjects consumed diets of about 2,550 calories, including 53 percent carbohydrates, 28 percent fat and 19 percent protein. In other words, the diets were identical.
Except for one thing. A whole grains group consumed 830 calories a day of whole-grain products. A refined grains group ate 830 calories of refined grain foods. In refining, also called milling, the grain loses much of its fiber, iron and B vitamins. The latter two are often added back to refined grains, but the missing fiber usually isn't. The whole grains came from commercial, off-the-shelf supermarket products made from whole flours, because the researchers wanted to use foods that are readily available to consumers.
During the last week of the six-week diet, investigators calculated the resting metabolic rate of subjects along with the energy content of their feces. (Amazingly only one subject from each arm of the experiment failed to manage the required collection.) The resulting measurements showed that the whole-grain eaters had a resting metabolic rate about 40 calories per day higher than the refined grain eaters, as well as a greater loss of calories (about 50) in their stool. Together, the two findings gave whole-grain eaters a 92-calorie gap in energy balance (calories in minus calories out) vs. the refined grain eaters.
"I think that's an amount many people would be happy about," says Roberts. "It's one and a half Oreo cookies a day." When the researchers extended this energy-balance deficit over a 12-month period, it translated to an annual weight loss of 5.5 pounds. This agreed almost exactly with a study of whole-grain consumption and weight change published by Harvard researchers in the New England Journal of Medicine in 2011. That report evaluated results from more than 120,000 subjects.
Some consumers have become so accustomed to soft, bland, refined grains that they disdain chewier whole grains. Yet in the Tufts experiment both whole grain and refined grain foods received equal palatability ratings.
It's easy to move gradually in the direction of greater whole-grain consumption, notes Roberts. Just introduce a few more foods made from whole-grain flours. (Using cracked grains or whole grains - like cooked brown rice or quinoa - might prove even healthier than flours. That's because the more intact the original grain, the longer it takes to digest.)
Americans consume an average of about 15 grams of fiber a day. In the Tufts study, the whole-grains group reached 39 grams a day while the refined grains group consumed 21 grams.
Most studies that produce a negative energy balance also report a decrease in resting metabolic rate. The opposite occurred in the Tufts study. "We don't know for sure why that happened," Roberts admits. "But I believe the strong trend toward fullness among the whole-grain eaters means the brain received no signals directing it to turn down metabolism."
In a related paper, the Tufts team reported their findings on the microbiome's reaction to a whole-grain diet. They found "a modest positive effect of whole grains relative to refined grains on the immunity response to pathogens."
The Tufts study was funded by the U.S. Department of Agriculture and the General Mills Bell Institute of Health and Nutrition. The authors declared that General Mills had no input on the data collection, analysis or interpretation.