Fiber, fiber, and more fiber! If you want to have a healthy gut and strong heart you must eat your fiber—at least that’s what the inundating marketing campaigns tell us on a daily basis. Thankfully, most scientific evidence also currently supports that diets rich in fiber are associated with an array of positive outcomes, chief among them healthy hearts and arteries protected from the ravages of atherosclerosis. However, the most challenging aspect has been figuring out just how the fiber we eat manages to protect our heart.
Now, investigators at the University of Wisconsin (UW)-Madison believe they have identified a metabolic pathway, mediated by a genus of gut bacteria called Roseburia, that supports a microbial connection between fiber and heart health. Findings from the new study—published recently in Nature Microbiology through an article entitled “Interactions between Roseburia intestinalis and diet modulate atherogenesis in a murine model”—identified a particular fatty acid as the mechanism behind certain protective effects of a high-fiber diet in a mouse model. Known as butyrate, this fatty acid is produced by bacteria, such as Roseburia, in the gut as they digest plant fiber.
In the current study, the researchers showed that mice harboring the butyrate-producing bacteria Roseburia and that also ate a high-fiber diet suffered from less atherosclerosis and had reduced inflammation compared to mice without the bacteria. Mice that hosted Roseburia but ate a low-fiber diet were not protected, because without fiber the bacteria produced little butyrate.
“Atherosclerosis has historically been considered a disease of lipid metabolism,” explained senior study investigator Federico Rey, Ph.D., a professor of bacteriology at UW-Madison, noting that controlling the disease has usually focused on lowering the levels of cholesterol and other fats in the blood. “But over the last few decades, it’s been revised to be considered a chronic inflammatory disease.”
So, the key to reducing atherosclerosis may be reducing overall inflammation, especially in the bloodstream. Keeping inflammation down depends in part on having a strong gut barrier.
“One important function of the gut is to keep our friendly bacteria at a distance,” added lead study investigator Kazuyuki Kasahara, Ph.D., a postdoctoral researcher in Dr. Rey’s laboratory.
When inflammatory molecules break off from beneficial bacteria and leech out of the gut and into the bloodstream, they can trigger widespread inflammation. To keep these molecules at bay, healthy gut cells form strong attachments to one another, creating an intact barrier. However, that attachment can be broken up.
“When that attachment gets loose, the gut becomes leakier,” Dr. Rey commented. Leaky guts lead to more inflammation.
To study butyrate’s effect on the gut and atherosclerosis, the research team colonized germ-free mice with specific communities of bacteria, either with or without the butyrate-producing Roseburia. Those mice were then fed diets either rich or lacking in fiber, which Roseburia processes into butyrate.
Interestingly, the investigators found that mice hosting Roseburia had lower levels of several markers of inflammation and a reduced extent of atherosclerosis—but only if they ate a high-fiber diet. Without fiber, Roseburia levels plummeted, and the mice were not protected from atherosclerosis. The researchers used mice genetically susceptible to atherosclerosis because mice do not naturally develop the disease.
To determine if butyrate was the true cause of Roseburia’s protective effects, Dr. Kasahara fed the fatty acid to mice without any butyrate-producing bacteria. Because pure butyrate would quickly be taken up by cells in the upper intestine, the mice were fed a slow-release version that made it intact to the lower guts.
The slow-release butyrate reduced the extent of fatty plaques by about a third, and reduced other markers of inflammation and atherosclerosis, suggesting that the fatty acid formed a major component of Roseburia’s anti-atherosclerosis effects.
Previous work indicated that humans with cardiovascular disease harbor lower levels of Roseburia and other butyrate-producing bacteria. The new study is one of the first to identify a clear cause for a previously mysterious link between dietary fiber, microbiomes, and health. However, the researchers caution that the results don’t point to butyrate as a new, simple supplement for heart health—fiber from whole foods still appears to be the ideal way to support a healthy gut.
“My wife gives me a hard time because every bread I buy is sprouted, high-fiber, whole grains,” Dr. Rey concluded about his years of study in this field. “And I eat oatmeal in the morning.”
