Through changing the composition of the human gut microbiome, a short-term, oat-based diet may effectively reduce cholesterol levels, according to two recent trials. The findings build on the cereal’s long-held status as a dietary intervention for diabetes.
“Today, effective medications are available to treat patients with diabetes,” says Marie-Christine Simon, junior professor at the Institute of Nutritional and Food Science at the University of Bonn, Germany.
“As a result, this method has been almost completely overlooked in recent decades. We wanted to know how a special oat-based diet affects patients.”
The 32 participants involved in the study were not diabetic, but were diagnosed with a metabolic syndrome linked to a higher risk of diabetes. This condition is characterized by high body weight, blood pressure, blood glucose, and blood lipid levels.
Two days produce meaningful results
The trial published in Nature Communications consisted of one two-day, high-dose oat intervention study, followed by a longer, low-dose six-week intervention study.
In the short-term trial, participants assigned to the oat group consumed three meals consisting of only 100 g of oats boiled in water daily for two days. This entirely replaced their habitual Western diet.
To determine any potential long-term effects, this short intervention was followed by a six-week follow-up period. In this time frame, participants in the oat group replaced only one habitual meal in their daily Western diet with 80 g of oatmeal. Those in the control group stayed entirely on a Western diet.
Oatmeal increased the number of certain beneficial bacteria in the gut.After six weeks, participants’ cholesterol levels significantly improved in comparison to the control group, where these levels remained stable. The researchers note that microbial phenolic metabolites produced in the gut microbiome appeared to contribute to the oat’s positive effects.
“The level of particularly harmful LDL cholesterol fell by 10% for them — that is a substantial reduction, although not entirely comparable to the effect of modern medications,” says Simon.
The oat-based diet’s positive effects were still evident at the end of the six week follow-up. “A short-term oat-based diet at regular intervals could be a well-tolerated way to keep the cholesterol level within the normal range and prevent diabetes,” Simon highlights.
Feeding healthy intestinal flora
Researchers took blood and stool samples before the participants made any changes to their diet. They also measured their blood pressure, weight, height, waist size, and body fat.
A second examination took place immediately after the two-day oat-based diet, followed by three others after two, four, and six weeks.
Based on the findings, the study’s lead author Linda Klümpen, from the University of Bonn, explains how oatmeal exerts its beneficial effect: “We were able to identify that the consumption of oatmeal increased the number of certain bacteria in the gut.”
“The microbiome has increasingly been the focus of research in recent decades. After all, it is now known that intestinal bacteria play a decisive role in metabolizing food. They also release the metabolic by-products that they create into their environment. They supply, among other things, the cells of the gut with energy, enabling them to better perform their tasks.”
Moreover, microbes impact the body through various gut-organ axes. “For instance, we were able to show that intestinal bacteria produce phenolic compounds by breaking down the oats,” notes Klümpen.
“It has already been shown in animal studies that one of them, ferulic acid, has a positive effect on cholesterol metabolism. This also appears to be the case for some of the other bacterial metabolic products.”
Meanwhile, other microorganisms in the gut dispose of the amino acid histidine. Without this process, the body turns histidine into a molecule that researchers suspect helps promote insulin resistance, which is a key characteristic of diabetes.
“As a next step, it can now be clarified whether an intensive oat-based diet repeated every six weeks actually has a permanently preventative effect,” Simon concludes.
