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Diet and lifestyle

Why eating whole-grain products is so healthy

New Danish research shows how healthy eating whole grains is. Compared with refined grains, whole grains lower the risk of cardiovascular disease and diabetes and cause people to lose weight. The probable reason is that, when people eat whole grains, they feel full and therefore eat less because they fill their stomach with dietary fibre. In addition, intestinal bacteria can convert whole-grain products into substances that reduce low-grade inflammation.

Whole grains are healthy! Okay, this is not a revelation, because researchers have known this for a long time. Nevertheless, a new Danish study has delved a little deeper into understanding why whole grains are really as healthy as they are.

The research results show, among other things, that whole grains reduce low-grade inflammation in the body and thus reduce the risk of cardiovascular diseases and type 2 diabetes. The probable reason is that intestinal bacteria love whole grains and convert them into substances that can reduce inflammation. Inflammation is known to increase the risk of all sorts of diseases, from diabetes to stroke. The study also showed that whole grains can help people to lose weight.

One type of whole grain seems especially to be a very good food to add to your meal planning if you want to be healthier.

“Rye very positively affects health and seems to be able to counteract inflammation. The conclusion to our study must be that if you are overweight and at risk of developing cardiovascular diseases or diabetes, you should eat some rye sandwiches,” says a researcher behind the new study, Tine Rask Licht, Professor, National Food Institute, Technical University of Denmark.

The new research results were recently published in Gut.

Human trials are difficult

The researchers more precisely examined how a whole-grain diet affected 60 overweight Danes.

This was a crossover study: the researchers put the trial participants on either a refined-grain diet or a whole-grain diet for their daily intake of bread, pasta, crackers and other grain-containing foods. The participants ate one of the two diets for 8 weeks, then had no specific diet for 6 weeks followed by 8 weeks with the alternative diet to what they had eaten in the first 8 weeks. So if they initially had eaten whole grains, they ate refined grains during the second 8-week period and vice versa.

The trial participants were basically healthy although overweight.

“The first measurable result of eating a diet with lots of whole grains was weight loss. Compared with a refined-grain diet, the test participants lost about 1 kg in 8 weeks on the whole-grain diet,” says Tine Rask Licht.

Whole grains fill you up

Tine Rask Licht attributes the weight loss on whole grains to a reduction in the measured overall energy intake, which is likely to result from an increased sense of being full (satiety) compared with refined grains.

The researchers had matched the whole-grain products with the refined-grain products so they contained about the same number of calories.

The participants ate food other than grains, such as meat and vegetables, but the researchers still found that the people who ate whole grains lost weight.

“They lose weight because they eat less. They eat fewer total calories when they eat whole grains, probably because the whole-grain products fill them up more than the refined-grain products,” explains Tine Rask Licht.

Whole grains reduce the risk of cardiovascular diseases and diabetes

However, people losing weight by eating whole grains is not the study’s eureka moment. It is that eating whole grains can reduce low-grade inflammation, which is known to affect the risk of developing cardiovascular diseases and diabetes.

The researchers did not investigate the actual development of cardiovascular diseases but instead measured markers of low-grade inflammation in the blood.

Such inflammation is associated with an increased risk of developing cardiovascular diseases and type 2 diabetes, and researchers can use blood tests to analyse the concentrations of various substances (markers) that indicate the body’s state of inflammation. The concentrations of these markers in the blood indicate the risk of developing the diseases.

The results show that a diet rich in whole grains can significantly reduce the concentrations of markers of low-grade inflammation in the blood and thus also the risk of developing cardiovascular diseases.

“The quantity of whole grains consumed is directly correlated with the decrease in the concentrations of markers of inflammation. This indicates that people at risk of developing cardiovascular diseases or diabetes, for example because of obesity, can benefit from eating lots of whole grains,” says Tine Rask Licht.

Rye is healthy

The researchers also examined which types of whole grains had the best effects on markers of inflammation.

In addition to using the blood tests to determine whether the trial participants had eaten whole grains, the researchers could use the signature of the different types of whole grains in the form of various markers to determine whether each participant had eaten predominately wheat, barley, rye or other grains.

The researchers thus compared the anti-inflammatory effect of different types of whole grains and found that consuming whole-grain rye especially benefited markers of inflammation.

“When the blood test showed that a participant ate a lot of rye, we could also see a clear anti-inflammatory effect that helps to protect against a wide range of diseases related to lifestyle. Whole-grain rye is clearly healthy,” says Tine Rask Licht.

No change in intestinal bacteria

Another part of the study involved stool samples. The researchers were convinced that eating whole-grain products would change the composition of intestinal bacteria.

Intestinal bacteria affect health in many ways. For example, healthy intestinal bacteria produce several substances that can reduce inflammation. Many of these healthy intestinal bacteria specialize in breaking down the fibre from certain types of whole grains, so the researchers were convinced that a diet with many whole-grain products would change the intestinal bacteria.

However, this did not happen.

“We were surprised that we did not find more change in the composition of intestinal bacteria. However, just because we could not find any effect does not mean it was not there. The bacterial community in the intestines is very complex, and there might have been an effect that was hidden by the individual variation between people. In addition, perhaps our trial participants already ate many whole-grain products, so the effect of the change in diet would affect the intestinal bacteria less strongly than the markers of inflammation and their weight,” says Tine Rask Licht.

Tine Rask Licht explains that the intestinal bacteria can nevertheless explain part of the anti-inflammatory effects of whole-grain products. When intestinal bacteria break down whole grains, they transform them into short-chain fatty acids, which are known to be anti-inflammatory.

“We had difficulty in precisely measuring any change in short-chain fatty acids in the blood in our study, but this could be an obvious explanation for the positive effects of whole grains,” concludes Tine Rask Licht.

"Whole grain-rich diet reduces body weight and systemic low-grade inflammation without inducing major changes of the gut microbiome: a randomised cross-over trial"  has been published in Gut. Researchers from The Novo Nordisk Foundation Center for Basic Metabolic Research participated in the research.

Tine Rask Licht
Professor
Humans have more bacteria in their gut than cells in their whole body. During the last decade, it has become clear that the gut bacteria exist in a symbiotic relation with the host, and play a pivotal role for host health – Particularly in the context of immune-related diseases. I am heading the research group on Gut, Microbes and Health, which primarily works within the areas of gut microbiota and food ingredients. We study the interplay between diet, intestinal microbiota and the immune system, and create knowledge that contributes to the development of healthy foods and ingredients, as well as to new strategies for alleviation of diseases that relate to the composition of gut bacteria.