More dietary fibre


Beneficial bugs (Photo: NIAID)

Be kind to your intestinal flora and it will be kind to you in return. We are talking about the microbiome, the trillions of bugs in your large intestine living in symbiosis with you.

We have written about the microbiome before. All the good deeds the bugs can do if you just feed them the right raw material. And dietary fibre is the ideal food source to support the needs of the beneficial bugs.

The fibre gap

Insufficient nutrients for our gut bacteria have been linked to a loss of certain beneficial bacterial species in western societies and are likely impacting our immunological and metabolic health. Most westerners consume only half of the amount of dietary fibre recommended by dietary guidelines. Nutritionists refer to this as the “fibre gap,” and it is a problem because dietary fibre is the primary source of nutrition accessible to gut bacteria in humans.

Scientists have long promoted the importance of strategically increasing dietary fibre intake as one path forward in regaining gut microbial biodiversity. Although this advice is far from new, the now proven depletion of the microbiome with a fibre deficient diet adds a new perspective to the western diet that we are currently eating.

Comparative studies between rural communities from Africa and South America and industrialised western communities from Europe and North America have revealed specific adaptations of their microbiomes to their respective lifestyles. These adaptations include higher biodiversity and enrichment of Bacteroidetes and Actinobacteria in rural communities, and an overall reduction in microbial diversity and stability in western populations.

Restoring fibre intake can have immediate effects

Some scientists are concerned that a dramatic shift away from a diet similar to the one under which the human-microbiome symbiosis evolved is a key factor in the rise of non-communicable disorders like obesity. There is also a lot of epidemiological evidence that food products containing dietary fibre can help prevent the development of colon cancer and reduce the incidence of coronary heart disease.

It is clear that people living in non-industrialised societies have an average intake of fibre that is much higher than the low norms of western societies. In an experiment scientists compared the effects of a traditional South-African and a modern American diet.  Twenty South Africans gave up their corn porridge and vegetable stews for burgers and fries. And 20 Pittsburghians sacrificed fast food staples for the low-fat, high-fiber fare that South Africans traditionally eat that contained 55 grams of daily dietary fibre. Surprisingly, the Americans had improved markers for colon cancer already within two weeks, while the South Africans showed the opposite effects.

The good news is the finding that changes in the microbiome are largely reversible within a single generation if the fibre intake is increased. However, there are also bad news. With several generations on a fibre deficient diet a progressive loss of diversity is seen, which is not recoverable. So your children and children’s children will lack some of the beneficial microbial species, indicating that extinctions can occur in only a few generations.

Convinced yet?


Eat more fibre-rich food

It is recommended to eat 25-30 grams of dietary fibres a day from a variety of foods rich in both insoluble and soluble fibre.

Foods higher in insoluble fibre include:

  • whole grain breads and cereals
  • the outer skins of fruit and vegetables
  • nuts and seeds
  • raw lentil, kidney beans and chickpeas

Foods higher in soluble fibre include:

  • fruits and vegetables
  • dried beans and lentils
  • oats

To help meet your daily dietary fibre requirements look at the below table from the Dietitians Association of Australia:

Food Fibre content
3/4 cup whole grain breakfast  cereal  4.5g
2 slices wholemeal bread 4.5g
1 apple (with skin) and 1 orange  5.5g
2 cups mixed raw vegetables 10g
1/4 cup legumes eg. baked beans 3g
Total 27.5g

The fight for your attention

Cravings for a doughnut might be blamed on the microbiome (Photo: Makoto Satsukawa)


You’re working along doing your usual stuff and suddenly you feel a hunger pang. And you don’t just feel hungry, you crave fatty food. If you had a Krispy Kreme doughnut ready you would gulp it down. But fortunately there is none within reach. There are conflicting signals and you change your mind. Now you have a craving for sugar and you stretch for the Coke. You know you shouldn’t but you still do it. What’s happening here?

Your microbiome at work

You remember the microbiome we have written about in previous blogs, the 100 trillion bacteria in your gut that outnumber your own cells about 100-fold? They help breaking down your food, fighting off infections and nurturing your immune system. It’s a lovely, invisible garden that play a crucial role in your well-being. However, even if it sounds like science fiction, it seems they are not content with limiting their activity to the gut, but may very well affect both your cravings and mood to get you to eat what they want.

Bacterial species vary in the nutrients they need. What that means is that some for instance prefer fat, and others sugar. The creepy part is that they not only vie with each other for the food they need to try to retain a niche within the digestive tract, they also try to make sure that you select the food they need. Different species of microbes thrive on different kinds of food. If they can prompt us to eat more of the food they depend on, they can multiply.

Researchers in reviewing the recent scientific literature concluded that microbes in the microbiome influence human eating behaviour and dietary choice to favour consumption of the particular nutrients they grow best on, rather than simply passively living off whatever nutrients you choose to send their way. There is a diversity of interests represented in the microbiome, some aligned with our own dietary goals, and others not. Of course it makes sense for them, but the question is how they have the means to influence what you eat.

Signalling systems at work

While it is unclear exactly how this occurs, the research team believes this diverse community of microbes may influence our decisions by releasing signaling molecules into our gut. This alone might not send any red flags, but because the gut is linked to the immune system, the endocrine system and the nervous system, those signals could influence your physiologic and even your own behavioural responses.

Research suggests that gut bacteria may be affecting your eating decisions in part by acting through the vagus nerve, which connects 100 million nerve cells from the digestive tract to the base of the brain. Microbes have the capacity to alter the neural signals in the vagus nerve, changing taste receptors, producing toxins to make you feel bad, and releasing chemical rewards to make you feel good.

Who is the puppet master?

Who is the puppet master? (Photo: Luc De Leeuw)


Fortunately, it’s not a one-way street. In turn your own diet choice will have a huge impact on the microbial population in your gut. It’s a whole ecosystem, and it’s evolving on the time scale of minutes. You can influence the composition of the microbiome by deliberately change what you eat, with measurable changes in the microbiome within 24 hours of a diet change.

This may be accomplished through food and supplement choices, by ingesting specific bacterial species in the form of probiotics, or by killing targeted species with antibiotics. Because the microbiome is easily manipulated by prebiotics, probiotics, antibiotics, fecal transplants, and dietary changes, altering our microbiota might offer a possible approach to otherwise difficult problems of obesity and unhealthy eating. Optimising the balance of power among bacterial species in our gut might allow us to fight obesity and live more healthier lives.

We are only beginning to scratch the surface of the importance of the microbiome for human health. Targeting the microbiome could open up possibilities for preventing a variety of diseases from obesity and diabetes to cancers of the digestive tract. Although it is early days, it might pay off to attempt to be in charge of what you eat, now when you know the sneaky impact of your own bugs. Try to be your own puppet master.

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