It hasn't been a great decade for fans of grain consumption – not even wholegrains. Popular diet books and many others have argued for limited grain consumption. Meanwhile, apparent scientific softening on the fat-is-bad-for-you dictum has increased interest in healthy fat consumption. That, too, has put grains, which are mainly composed of carbohydrates, on trial.
Nonetheless, a recent and highly controlled study in the American Journal of Clinical Nutrition lends support to wholegrain consumption, especially in comparison to refined grains. The conclusions line up with the US Dietary Guidelines 2015-2020, which recommend that carbohydrates make up 45 to 65 per cent of a healthy diet, with 170 grams from grains.
The new study, conducted at Tufts University's highly regarded Jean Mayer USDA Human Nutrition Research Centre, found that a diet high in wholegrains versus refined grains led to a favourable energy balance. In other words, subjects on a wholegrain diet burned more kilojoules 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 wholegrain consumption and reduced body weight and adiposity".
Senior author Susan B. Roberts, professor of nutrition and senior scientist at the USDA Nutrition Centre at Tufts, agrees that many people eat too many highly processed and often highly sugared grains. She doesn't, however, find this a good reason to limit wholegrains. "I think the anti-carb hype has gone too far for a healthy society," she says. "We should remember that wholegrains 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, wholegrains 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 fibre. Wholegrains also increase the antioxidant level of a diet, which is important for health."
Unlike many much-publicised nutrition studies, this one was not designed for kilojoule restriction or weight loss. Instead, researchers constantly monitored subjects' weights to make sure no one was dropping kilograms. With that variable eliminated, they could focus more intently on the wholegrains versus refined grains question at the centre of their investigation.
Eighty one subjects were divided into two groups who picked up all their meals each day at the Tufts nutrition centre. Subjects had an average age in their mid-50s and an average body mass index (BMI) of 25.6, slightly above the 25 upper limit of healthy BMI, but not overweight or obese. During the six weeks of diet manipulation, all subjects consumed identical diets of about 10,670 kilojoules, including 53 per cent carbohydrates, 28 per cent fat and 19 per cent protein.
Except for one thing. A wholegrains group consumed 3473 kilojoules a day of wholegrain products. A refined grains group ate 3473 kilojoules of refined grain foods. In refining, also called milling, the grain loses much of its fibre, iron and B vitamins. The latter two are often added back to refined grains, but the missing fibre usually isn't. The wholegrains 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 faeces. (Amazingly only one subject from each arm of the experiment failed to manage the required collection.) The resulting measurements showed that the wholegrain eaters had a resting metabolic rate about 167 kilojoules per day higher than the refined grain eaters, as well as a greater loss of kilojoules (about 209) in their stool. Together, the two findings gave wholegrain eaters a 385-kilojoule gap in energy balance (kilojoules in minus kilojoules out) versus 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 2.5 kilograms. This agreed almost exactly with a study of wholegrain 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 wholegrains. Yet in the Tufts experiment both wholegrain and refined grain foods received equal palatability ratings.
It's easy to move gradually in the direction of greater wholegrain consumption, notes Roberts. Just introduce a few more foods made from wholegrain flours. (Using cracked grains or wholegrains – 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. Try these alternative grains.)
Americans consume an average of about 15 grams of fibre a day. In the Tufts study, the wholegrains 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 wholegrain 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 wholegrain diet. They found "a modest positive effect of wholegrains relative to refined grains on the immunity response to pathogens."
The Tufts study was funded by the US 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.
The Washington Post