Individuals also absorb the sugars from some processed whole grains more quickly than they do those from intact whole grains, triggering blood sugar spikes that can “possibly increase hunger, lead to overeating and increase the risk for diseases related to insulin resistance, like diabetes and heart disease,” says David Ludwig, a professor of nutrition at the Harvard School of Public Health. For instance, bread made from 80 percent–whole-wheat kernels is absorbed much more slowly than bread made from ground whole wheat. When a person eats intact grains, the body has to break down the outer bran before digesting the inner endosperm and germ. Ground grains often don’t provide these metabolic brakes.
But even when whole grains aren’t ground, they can be processed in ways that can cause metabolic problems. In a 1999 study Ludwig and his colleagues split 12 obese teenage boys into groups. Some were given a breakfast of instant oatmeal, in which whole oats have been rolled and steamed so that they cook quickly. Other boys were given steel-cut oatmeal, comprising whole oats that have been sliced but not steamed. Although both meals had the same calorie and fiber content, the instant oats triggered much larger blood sugar spikes (a reflection of how quickly they were absorbed) and caused the boys to consume 53 percent more calories at lunch than the boys who ate the steel-cut oats. (A third group of boys were given identically caloric breakfasts of vegetable omelets and fruit and ate 81 percent fewer calories at lunchtime than did the instant oat eaters.) Food companies lump ground whole grains, partially processed grains and intact unprocessed grains together under the same broad category of “whole grains,” so it’s difficult for consumers to know which they’re getting.
Whole-grain foods can also contain unhealthy additives. In January Ludwig and other Harvard researchers compared the nutrient composition of 545 grain products and found that those labeled with the “Whole Grain” stamp, an industry-sponsored label for foods containing at least eight grams of whole grains per serving, contained more calories and sugar than those without the stamp. They were also more expensive. When a food is marketed as containing whole grains, “it takes on a ‘health halo,’ and companies can slip in all sorts of junk without people recognizing what they're getting,” Ludwig says. Joanne Slavin, professor of food science and nutrition at the University of Minnesota, who served on the committee for the 2010 Dietary Guidelines for Americans, agrees that many foods with whole-grain labels are “really not very nutritious food products.”
More isn’t good
So how did “whole grain” become synonymous with “healthy”? Part of the confusion stems from the U.S. dietary guidelines, which recommend that individuals triple their consumption of whole-grain foods from an average of one ounce per day to three ounces. But the goal is for Americans to replace half of their refined grains with whole grains, not to eat whole grains in addition to the refined ones they have been eating, Slavin explains. “We don’t want people to think that because a food has whole grains, they should eat more of it,” she says. “Grains in general are overconsumed in the U.S.”