A short, intensive oat-based diet may lead to lasting improvements in cholesterol levels, according to a small, randomized trial that tested how the body responds to a concentrated intake of a familiar whole grain.
In the study, published in Nature Communications, adults with metabolic syndrome followed a calorie-reduced diet centered almost entirely on oatmeal for two days. Researchers found that LDL cholesterol, often described as “bad” cholesterol, fell by about 10% compared with a control group that also reduced calories but did not eat oats. Notably, the cholesterol changes in the oat group were still evident six weeks later.
The research was conducted by scientists at the University of Bonn. Participants had metabolic syndrome, a cluster of conditions that includes excess body weight, high blood pressure and abnormalities in blood sugar and lipid metabolism.
During the two-day intervention, participants ate about 300 grams of oatmeal per day, prepared with water and eaten at three meals. They were allowed small amounts of fruit or vegetables but otherwise followed a highly restricted diet that provided roughly half of their usual daily calories. A separate group followed a calorie-reduced diet without oats.
Both groups saw some health improvements, which the researchers attributed in part to calorie reduction. However, the changes were more pronounced among those who followed the oat-based diet. In addition to lower LDL cholesterol, they lost an average of about two kilograms and saw small reductions in blood pressure.
“The level of particularly harmful LDL cholesterol fell by 10 percent for them,” said Marie-Christine Simon, a junior professor at the University of Bonn and senior author on the study. She noted that while the effect was meaningful, it was “not entirely comparable to the effect of modern medications.”
To understand why oats appeared to have an added benefit, the researchers examined changes in the gut microbiome and in microbial byproducts found in blood and stool samples. They found that the oat-based diet increased certain gut bacteria and boosted levels of phenolic compounds produced when microbes break down components of oats. Some of these compounds have previously been linked, in animal studies, to improved cholesterol metabolism.
At the same time, other microbial changes appeared to reduce the availability of histidine, an amino acid that can be converted into molecules suspected of contributing to insulin resistance. Together, these shifts may help explain why the metabolic effects of the short oat intervention persisted beyond the two-day diet itself.
The researchers also tested a more moderate approach, in which participants ate 80 grams of oats per day for six weeks without other dietary restrictions. That longer but less intensive intervention led to only small changes, suggesting that the cholesterol effects observed in the study depended on both the amount of oats consumed and the accompanying calorie reduction.
“A short-term oat-based diet at regular intervals could be a well-tolerated way to keep the cholesterol level within the normal range,” Simon said, while emphasizing that further research is needed to determine whether repeating such an intervention would be practical, safe or effective over the long term.
The study has important limitations. It involved a small number of participants, relied on a highly controlled and restrictive diet that most people would not follow routinely, and could not fully separate the effects of oats from those of short-term calorie reduction. The authors stress that the findings do not suggest oats alone can replace cholesterol-lowering medications or that extreme short-term diets are appropriate for everyone.
Instead, the results add to evidence that whole grains like oats can influence cholesterol metabolism, particularly in people at higher metabolic risk, and that short, intensive dietary changes can sometimes produce effects that last longer than the intervention itself.
The trial was funded by the German Federal Ministry of Education and Research, the German Diabetes Association and the German Research Foundation, with additional support from the German Cereal Processing, Milling and Starch Industries’ Association and RASO Naturprodukte.