Does a high-fibre diet help relieve asthma?
"Eating more fibre could help treat symptoms of asthma, scientists say," The Independent reports. This headline is based on a mouse study that looked at the role that different types of dietary fibre play in the gut and its effect on allergic airway inflammation.
Allergic airway inflammation – which happens in conditions such as asthma – is where the immune system mistakes harmless triggers such as dust mites as a threat. This causes the airways to become inflamed, leading to symptoms such as wheezing and breathlessness.
Allergic asthma cases are increasing in developed countries, which are also seeing fewer people eating a high-fibre diet. The researchers wanted to see if there could be a possible association between the two.
To do this, they carried out a series of laboratory and animal experiments on mice and found that mice given diets high in soluble fibre (a human equivalent would be fruit and vegetables) had more of a protective effect on lung inflammation compared with mice given different types of fibre.
It's important not to interpret the findings as being definitely applicable to people, but they are a good starting point for further study in humans.
Eating a high-fibre diet is recommended, even if it turns out to be an ineffective way of preventing asthma. It may help prevent heart disease, diabetes, weight gain and some cancers, and can also improve digestive health. Read more about why fibre is important.
Where did the story come from?
The study was carried out by researchers from the University of Lausanne in Switzerland and was funded by a grant from the Swiss National Science Foundation. It was published in the peer-reviewed journal Nature Medicine.
This study was covered appropriately by the UK media, although some of the headlines implied that the study was conducted in humans, which is not the case.
What kind of research was this?
This was laboratory and animal research looking at what role dietary fibre plays in the gut and influencing lung inflammation in mice.
Fibre is only found in foods that come from plants. There are two different types of fibre – soluble and insoluble. Soluble fibre can be digested by your body and is found in fruit and vegetables, oats and golden linseeds.
Soluble forms of fibre can "ferment" in the gut and be converted to short-chain fatty acids. These are often termed essential fatty acids as they cannot be manufactured by the body, but are essential building blocks for long-chain fatty acids. These have a variety of roles, including in neurological function and immunity.
Insoluble fibre can't be digested by your body. It passes through your gut without being broken down and helps other foods move through your digestive system more easily. Examples of foods that are sources of insoluble fibre include wholemeal bread, cereals and nuts.
What did the research involve?
The research involved a series of animal and laboratory experiments. In one of the experiments, a group of mice were fed either a normal-fibre diet or a low-fibre diet. All of the mice were then exposed to house dust mites (a common trigger for asthma symptoms in humans) and were monitored for up to six days to see if there was any allergic airway inflammation.
Another experiment was performed on a second group of mice where increased amounts of fibre were given. Mice were either given the normal-fibre diet plus cellulose (a poorly fermentable fibre – this served as a control) or a normal-fibre diet plus pectin (readily fermentable fibre), and all underwent the same monitoring for airway inflammation.
The researchers then analysed the effect of dietary changes on the microbial population (levels of micro-organisms such as bacteria) of the gut and lung tissue of the mice, among other various experiments.
What were the basic results?
The main results of the study were:
- Mice given a low-fibre diet had stronger allergic reactions to house dust mite than mice fed a normal-fibre diet.
- Mice fed a pectin-rich diet (readily fermentable fibre) had more of a protective effect on lung inflammation compared with mice fed a poorly fermentable fibre diet.
- Dietary fermentable fibre changed the composition of the gut and lung microbiota (the types of species making up the population of bacteria) of mice. The gut microbiota metabolised the fibre and increased the concentration of short-chain fatty acids, which may promote better health.
- Mice fed a high-fibre diet had increased circulating levels of short-chain fatty acids and were protected against allergic inflammation in the lung compared with mice fed a low-fibre diet, who had decreased levels of short-chain fatty acids and increased allergic airway inflammation.
How did the researchers interpret the results?
The researchers conclude that dietary fibre and short-chain fatty acids can shape the immunological environment in the lung and influence the severity of allergic inflammation. They say dietary fibre changes the composition of the gut and increases the circulating levels of short-chain fatty acids, which helps impair allergic airway inflammation.
One of the researchers, Dr Benjamin Marsland from the University of Lausanne, is quoted by the BBC as saying, "There's a very high probability it works in humans; the basic principle of fibre being converted to short-chain fatty acids is known.
"But we don't know what amount of fibre would be needed, and the concentrations of short-chain fatty acids required might be different. It is early days, but the implications could be far reaching."
Conclusion
The current study has discovered more about the role of dietary fibre in the gut and its effect on lung inflammation. The findings come from experiments with mice in the laboratory.
Importantly, the researchers only tested the effect of dietary fibre on airway inflammation in mice. The results of animal research often do not translate into the same results for people.
However, the basic biology of humans and mice is surprisingly similar in some aspects, so these findings give a good starting point for further study in humans.
Although these results can help scientists learn more about the role dietary fibre plays in protecting against airway inflammation, headlines stating that a high-fibre diet "prevents lung inflammation" are premature.
However, there is evidence that a high-fibre diet can protect against other chronic diseases. For example, a 2011 study found evidence that suggested a high-fibre diet could protect against bowel cancer.
If you are having problems controlling your asthma symptoms, your treatment plan may need to be reviewed. Read more about the available treatment options for asthma.
