Refined grains can be a dangerous business. They are digested quickly, flooding the bloodstream with a wave of sugar and stressing the pancreas, the latter of which compensates by producing spikes of insulin. Eventually, those sugar bursts can result in obesity, diabetes, and heart disease. But starting in the 1990s, nutrition experts began offering Americans an enticing deal: You can still eat your bread and pasta, as long as you avoid those dangerous refined grains and accept the salvation of whole grains.
Dozens of studies showed that whole-grain consumption was linked with a lower risk of cancer, cardiovascular disease, and diabetes. By 2015, the Dietary Guidelines for Americans was recommending making whole grains at least half of one’s total grain consumption. Grocery stores were soon filled with delicious whole-grain snacks, cereals, and shelf-stable breads, each promising a shortcut to health. When Robert F. Kennedy Jr. unveiled his inverted food pyramid this past January—which demoted whole grains to the narrowest tip and elevated animal products—some nutrition experts cried foul, concerned that Americans would abandon a category with decades of science behind it.
Nutritionists broadly concur that unrefined foods of all sorts, including oats, vegetables, seeds, and nuts, are a healthier choice than foods that have been heavily processed. At the same time, many researchers suspect that the whole grains on grocery shelves are a fiction. No one can actually agree on what a whole-grain food is. And the whole-grain products Americans most commonly eat behave in the body much the same as the refined-grain foods they were meant to replace.
A whole grain, in principle, is a grain—wheat, rice, oats—that retains all three of its original components. Those components are layered a bit like an egg: The bran is the sturdy eggshell, dense in fiber. The starchy endosperm is the biggest part of the grain, akin to the egg white. Buried at the center is the yolk-like germ, rich in vitamins and phytonutrients. Refined grains, such as white flour, have been stripped of their fibrous, nutritious bran and germ, leaving primarily the starch and a bit of protein behind.
A whole-grain food—the pasta, bread, and breakfast cereals that you actually buy and eat—is a different matter entirely. The 2025–30 Dietary Guidelines for Americans describes a whole-grain food simply as one that contains bran, endosperm, and germ. The industry-sponsored Whole Grain Council grants its “basic stamp” to any product with at least eight grams of whole-grain ingredients in each serving, but it places no restrictions on what might fill the rest of the package. The FDA counts as a whole-grain product any food whose grain content is at least 51 percent whole grain. Walter Willett, a professor of epidemiology and nutrition at Harvard, told me that such definitions are “obviously misleading.” Several bills have been introduced to Congress that would require food companies to disclose a product’s actual whole-grain content as a percentage of total grain, but they have all died without a vote.
This inconsistency makes studying the health effects of whole grains challenging. A 2022 study applied five competing institutional definitions of whole-grain foods to dietary data from approximately 40,000 Americans. The authors found that the same person could be a consumer of a high amount of whole grains under one standard and of a low amount under another. They also found that the food category that most commonly qualified as “whole grain” was ready-to-eat breakfast cereals, which are among the most heavily processed foods in the grocery store; many of them are high in added sugar and lacking in fiber. Another analysis concluded that foods bearing the Whole Grain Council stamp contain more calories and added sugar on average than products without it.
It should be no surprise, then, that when scientists examine whole grains more closely, some claims about their health effects begin to crumble. For instance, a 2022 study Willett co-authored followed more than 200,000 Americans for 25-plus years. The team found that foods such as brown rice and oatmeal reduce the risk of coronary heart disease but that popcorn—technically a whole grain under any definition—does not. And in a small randomized trial from 2009, whole-wheat bread produced a higher blood-sugar spike than white pasta did, despite the fact that the bread contained five times as much fiber as the pasta. In other words, a refined-grain product clearly outperformed a whole-grain product on the very metric on which whole grains are supposed to win.
It’s still not clear what is driving those inconsistencies. But some researchers have an idea: Perhaps, instead of the presence of bran and germ, what matters is the physical architecture of the grain itself, including how tightly its molecules are packed together. Most commercial whole-grain breads and cereals are “molecularly disassembled,” Dariush Mozaffarian, a cardiologist and a nutrition researcher at Tufts University, told me. Bran, endosperm, and germ may be sourced from different factories and then recombined into a new food product. Compared with intact grains such as brown rice and corn kernels from the cob, molecularly disassembled whole grains are digested more quickly and, just like refined grains, spike your blood sugar faster and leave you hungrier sooner, which may contribute to metabolic disease over time.
Even if the grain’s components aren’t sourced separately, structure seems to matter. In one small 2022 study, a team of researchers matched whole-grain and refined-wheat products for every possible physical property: They ground them to the same particle size, prepared them in the same food form (in this case, porridge), and sourced all samples from the same batch of wheat at the same mill. Participants ate the matched products, and researchers measured blood-sugar response. The whole-grain advantage vanished. An earlier study from the University of Otago, in New Zealand, had a small group of adults with type 2 diabetes eat a variety of 100 percent whole-grain foods that differed only in milling method. After two weeks, the participants who were eating less processed whole grains had lost about a pound of body weight while those eating finely milled equivalents gained about the same amount. And even for products that have been finely milled, the final structure of the product seems to matter, because denser foods resist rapid digestion. Bread and pasta, for example, are both made from flour, but only pasta is extruded under pressure, compacting the starch into a dense matrix that digestive enzymes access slowly.
Disrupting the structure of a whole grain may also change how it affects the microbiome. When a grain is highly processed, its starch gets rapidly broken down in the small intestine, spiking your blood sugar but never reaching the colon, where most gut bacteria live. In a less processed grain, some of that starch travels further, arriving to the colon intact, Mozaffarian explained. In theory, the colon microbiome then feeds on that starch to produce hundreds of beneficial compounds that have positive effects on other organs. Plus, during processing, many commercial whole-grain breads have their natural insoluble fibers extracted and replaced with a soluble fiber such as inulin, Bruce Hamaker, a professor of food science at Purdue University, told me. Soluble fibers can improve the texture of the bread and help it retain moisture to keep it fresher longer. But that comes at a cost—those natural fibers selectively nourish a group of gut bacteria that help reduce inflammation and reinforce the intestinal barrier.
Without a label to indicate whether a grain’s structure has been disrupted before it goes into your food, choosing the healthiest grains can be difficult. Mozaffarian recommends looking for products that contain no more than 10 times as many grams of carbohydrate as grams of fiber—a rough proxy for structural and fiber integrity. He also recommends a rubric that requires no math: “Imagine putting the product into a cup of water and coming back four hours later,” he said. “If it’s a mush, it tells you it’s going to be rapidly digested. If it looks mostly the same, it probably has some natural intact structure.”
None of this means that people should abandon whole grains in favor of meat and whole milk. What it suggests, rather, is that the benefits scientists have been measuring may be only a fraction of what minimally processed whole grains can actually do.
*Sources: Sepia Times / Getty; Bildagentur-online / Getty; J. Magee / The New York Historical / Getty.
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