Foods rich in wholegrains have been associated with lower risk of developing type 2 diabetes and cardiovascular disease. However, the content of dietary fibre and bioactive compounds, such as lignans, differ between cereals. In a new study, researchers from Chalmers University of Technology show that wholegrain rye lowers serum LDL-cholesterol compared to wholegrain wheat. The effect was linked to the composition of the gut microbiota of the individual. There was no difference in glucose metabolism between wheat and rye diet, and lignan supplementation did not affect any parameter.
High wholegrain intake is associated with lower risk of developing non-communicable diseases such as type 2 diabetes and cardiovascular disease. In a new study, recently published in The American Journal of Clinical Nutrition, effects on metabolic parameters and risk factors was assessed between wholegrain wheat and rye for the first time, in subjects with so-called metabolic syndrome. People with metabolic syndrome have increased risk of cardiovascular disease and have elevated risk factors such as high blood pressure, high levels of blood cholesterol, obesity or abdominal obesity.
Lignan supplements to rye diet
There is a difference of dietary fibre quality in wholegrain wheat and rye, and the cereals also have different contents of bioactive compounds. Rye has the highest content of both dietary fibres and bioactive compounds. For example, wholegrain rye is rich in lignans, so-called phytoestrogens, which are substances that are similar to the hormone oestrogen.
Various studies have shown that lignans have protective effects against the risk of developing hormone-dependent cancers, such as breast cancer and prostate cancer. Recently, several studies have also shown that the levels of enterolactone and entradiol, molecules formed by the gut microbiota when degrading plant-based phytoestrogens, are strongly linked to reduced risk of developing type 2 diabetes.
"We wanted to see if supplementation of lignans could enhance the effect of wholegrain rye. We added more lignans to the subjects' rye diet than any other study has done so far, and we measured the highest levels ever detected of enterolactone and enteradiol in humans. Despite this, we saw no effects on glucose turnover and metabolic risk factors. This is an indication that phytoestrogens are not enhancing the positive effects of the rye," says Rikard Landberg, Professor of Food and Nutritional Science at Chalmers.
Lower cholesterol levels dependent on gut microbiota
The researchers showed, though, that cholesterol blood levels can be lowered with the intake of wholegrain rye. This has also been confirmed in recent, unpublished, studies. In addition, they discovered that the decrease of cholesterol levels was dependent on the subjects’ gut microbiota in the beginning of the trial. This provides a possible mechanistic link between dietary fibre-rich foods, microbiota and lipid metabolism.
"More studies are needed to investigate the mechanisms behind these results. Interestingly, only one of three enterotypes, (i.e. the sets of microorganisms found in the gut), was linked to lowering cholesterol levels. This may be the result of high levels of short chain fatty acids generated by this enterotype. There have been drug development studies where the gut microbiota was shown to boost the effect of lipid-lowering drugs. But the exact role of gut microbiota in the cholesterol turnover is still to be unrevealed and more studies are needed," says Rikard Landberg.
The cholesterol levels of the subjects were, however, back to normal after four to eight weeks.
"We have seen this in other studies as well. This may be due to the subjects getting tired of eating the intervention diet, in other words lack of compliance. It might also happen because, for some reason, you get an adaptation effect," says Rikard Landberg.
Want to investigate the potential of enterotype adapted diet
New studies focus on screening individuals with different enterotypes and evaluating the effects of fermentable fibres compared to non-fermentable fibres on metabolic risk factors across enterotypes. The researchers hope this will confirm the results from the recently published study. They will also get an estimate of how much greater the potential for prevention is with a diet adapted for the gut microbiota compared to diet that is not.
More about the study
- Read the article in The America Journal of Clinical Nutrition: Effects on whole-grain wheat, rye, and lignan suplementation on cardiometabolic risk factors in men with metabolic syndrome: a randomized crossover trial
- The current study was a collaboration between researchers at the Division of Food and Nutrition Science, the Danish Cancer Society Research Center in Copenhagen, Denmark, Uppsala University and Aarhus University, Denmark.
- 40 men with a risk profile for metabolic syndrome were randomly assigned diets of wholegrain rye or wholegrain wheat in an 8-week crossover study, in which all subjects received both treatments but in reverse order.
- The rye diet was supplemented with additions of lignans at weeks 4–8.
Contact
- Full Professor, Food and Nutrition Science, Life Sciences