A serendipitous conversation led Brian Bull, MD, to an important discovery about the human gastrointestinal system.

“Maureen and I ran across a functioning grain mill on a vacation to the Lake District of England in the late 1990s,” notes Brian Bull, MD, who recently retired as chair of professor of pathology and human anatomy at Loma Linda University School of Medicine.

Although the couple intended to stay only 45 minutes touring the picturesque town of Boot with its 700-year-old stone mill, the tour ended up lasting several hours when something the miller said caught Bull’s attention.

“The miller had a very large library,” Bull recalls. “He was not only keeping the large millstones in good running order, he was also a scholar and very knowledgeable about the grain-milling process. One of the things he stressed was that the large millstones in a working mill have to be taken apart every few months for dressing.”

The miller explained that dressing the stones involved removing a varnish-like coating that blurs their sharp right-angle edges.

“The millstones never touch,” Bull points out, “but they have grooves cut into the grinding surfaces. As the grooves of one stone go over the grooves of the other, they ‘scissor’ the grain. But when varnish—which is the residue of volatile oils in the grains—builds up between them, that can’t happen.”

The miller said that all grain was stoneground until steel milling technology was introduced in the late 1890s. “By the early 20th century, steel mills had completely taken over,” Bull reports.

Although the new technology produced a popular, very white flour, it came at an unforeseen cost.

“The miller explained that steel mills, with their very fine tolerances, could pop the wheat germ out of the grain before milling actually began,” Bull adds. “They could also remove all of the wheat bran.”

Because all the volatile, wheat-germ oils that used to coat the millstones were now missing, the result was bran-free flour. Unlike stoneground flour, white flour can be stored at room temperature without going rancid. “This flour is the foundation on which the fast food enterprise is built,” he explains.

As a result, a major source of fiber, wheat germ, and wheat-germ oils in the Western diet disappeared almost overnight.

"“That meant a very significant source of nutrition for the gut bacteria in the large intestine was gone. Now flour, minus the bran and germ, was just pure carbohydrate (starch) and protein (gluten). We absorb both of these nutrients in the small intestine. There is nothing left for the gut bacteria to live on"Brian Bull, MD

“In the large intestine,” he continues, “there are many species of bacteria that break down bran and other types of fiber. These are the bacteria that make Vitamin B-12, Vitamin K, and a whole lot of other compounds—such as short-chain fatty acids—that act in beneficial ways throughout the body, including the brain. But all of this gets disrupted because of the change in milling.”

Bull says science knows very little about the bacteria in the human digestive tract.

“Most of what gut bacteria do is good,” he reports, “but that isn’t true when it comes to their role in processing red meat. Red meat, after the gut bacteria get through with it, turns into a toxin that inhibits the metabolism of spent cholesterol, thereby allowing it to build up in the body.”

Although the toxic potential of red meat was discovered and reported about 18 months ago, Bull says most journalists love hamburgers, so they didn’t cover the story.

“Lack of fiber in the diet—wheat bran used to be a major source—can lead to medical complications such as diverticulosis and diverticulitis,” he observes

The first term describes a condition in which small, unwanted pockets balloon out from the gut wall. It causes gassiness, bloating, and abdominal swelling. If it progresses far enough, however, it can lead to diverticulitis, a deadly disease from which 300,000 people suffer each year in the US. Bull says many of those afflicted will die.

“Modifying your diet to include more whole-grain flour and so more fiber,” he insists, “can make an enormous difference in your gastrointestinal health.”

When Bull and his wife, who is also a physician, returned to the United States, he set out to develop a breakfast cereal to replenish the missing bran, wheat germ, volatile oils, and fiber that the human digestive tract needs. View his oat bran cereal recipe. 

Bull says he and Maureen have been eating his mill-inspired cereal for breakfast every day since the late 1990s. The fit, slender Bull, who is also free of gastrointestinal bloating, is a walking endorsement for the product. He adds that readers interested in eating well should add whole-grain bread to their diet along with fruits such as raspberries, blackberries, and apples, all of which are high in soluble fiber.

“Don’t buy bran cereal that lists microcrystalline cellulose among its ingredients,” he concludes. “It’s basically high quality sawdust.”