Although the subjects tested in the current trial were not diabetic, they suffered from metabolic syndrome associated with an increased risk of diabetes. Features include excess body weight, high blood pressure, elevated blood sugar levels, and lipid metabolism disorders. “We wanted to know how a particular oat-based diet affects patients,” explains Simon, who is also a member of the transdisciplinary research area “Life and Health” and “Sustainable Futures” at the University of Bonn.
300 grams of oatmeal per day
The participants were asked to eat exclusively porridge three times a day, which they had previously boiled in water. They were allowed to include only a few fruits or vegetables in their meals. A total of 32 women and men completed this oat-based diet. He ate 300 grams of porridge every two days and consumed only about half his normal calories. A control group was also placed on a calorie-reduced diet, although it did not include oats.
Both groups benefited from the change in diet. However, the effect was more pronounced for participants following an oat-based diet. “Their levels of particularly harmful LDL cholesterol fell by 10 percent – this is a huge reduction, although not entirely comparable to the effects of modern drugs,” Simon stressed. “They also lost an average of two kilos in weight and their blood pressure dropped slightly.”
Effects on LDL cholesterol, in particular, are likely to be relevant to health. If its quantity in the blood is too high, it gets deposited in the vessel walls. These deposits, known as plaque, narrow the blood vessels. In addition, congestion can burst due to an increase in blood pressure after, for example, physical exertion, anger or stress. As a result, a blood clot may form at the affected area, completely blocking the blood vessel. Alternatively, parts of the plaque may bleed with the blood and cause a heart attack or stroke.
Oats promote growth of “healthy” intestinal bacteria
But how does oatmeal exert its beneficial effects? “We were able to identify that oatmeal consumption increased the numbers of certain bacteria in the gut,” explains Simon’s colleague Linda Klumpen, lead author of the trial. 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 food metabolism. They also release the metabolic by-products they create into their environment. Among other things, they provide energy to the intestinal cells, enabling them to perform their functions better.
In addition, the microbes send some of their products into the bloodstream around the body, where they can have various effects. “For example, we were able to show that intestinal bacteria break down oats to produce phenolic compounds,” says Klumpen. “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 other bacterial metabolic products.” At the same time, other microorganisms “dispose of” the amino acid histidine. Otherwise the body converts it into a molecule suspected of promoting insulin resistance. This insensitivity to insulin is a key feature of diabetes mellitus.
A large amount of oats for two days is better than a small amount for six weeks
The positive effects of the oat-based diet were still visible after six weeks. “Short-term oat-based diets at regular intervals could be a good way to keep cholesterol levels within normal limits and prevent diabetes,” says Junior Professor Simon. However, in the current study, the whole grain exerted its effect in higher concentrations and with a reduction in calories: a six-week diet, in which participants consumed 80 grams of oats per day, with no other restrictions, yielded smaller effects. Simon adds, “As a next step, it can now be clarified whether an intensive oat-based diet repeated every six weeks really has a lasting preventive effect.”
test method:
A total of 68 participants took part in the trial. For the two-day short-term oat-based diet, all 17 participants on the oat-based diet and 15 participants on the control diet successfully completed the study phase. Two participants in the control group withdrew for personal reasons. For the six-week long-term oat-based intervention, 17 participants in the study group and the same number in the control group participated till the end. The sample size of 17 participants per group was calculated by the researchers based on data from earlier conventional trials.
The two-day intensive diet and the six-week trial with moderate doses of oats were both randomized controlled trials. In these “RCTs”, test subjects are randomly divided into two groups (i.e. randomized). One of them receives the potentially active ingredient – in this case oats –, but the other (the control group) does not. Ideally, test subjects are “blind”: they do not know which group they belong to. This rules out any placebo effect.
In nutritional experiments, blinding is often not possible – the people involved ultimately know what they are eating. This was the situation in these studies also. However, the evaluation of the blood and stool samples was actually “blind”: the researchers in charge were not informed whether the material was taken from members of the test group or the control group. The same applies to measuring blood pressure and weight. This ruled out the possibility of the scientists’ expectations of the results being wrong.
Blood and stool samples were taken before participants made any changes to their diet. Their blood pressure, weight, height, waist size and body fat were also measured. The second test took place immediately after the two-day oat-based diet, followed by three more tests after two, four and six weeks. The same analysis was performed at these four visits during the initial investigation and further blood and stool samples were collected. Researchers took the same approach during a second nutrition study, in which participants consumed 80 grams of oatmeal per day for six weeks.
Among other things, the blood samples were tested in the laboratory for LDL cholesterol content. The researchers also measured the concentration of a key molecule, dihydroferulic acid. This phenolic compound is probably formed by certain intestinal bacteria, which are known to have health-promoting effects.
By examining stool samples, researchers were able to confirm this hypothesis. They isolated a substance known as 16S RNA from the samples. This is a molecule that occurs exclusively in bacteria, but varies somewhat between different species. Thus a 16S RNA molecule can be used, like a fingerprint, to identify the bacterium from which it originated. The researchers also analyzed which metabolic products were present in the stool.
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