Guest blog by Dr Joanna McMillan.

The link between whole grains, cereal fibre and a healthy gut

While a healthy diet includes a wide variety of foods to provide the full range of nutrients, research shows there are particular benefits that come from the whole grains and cereal fibres in the food we eat.

A recent Lancet review found a low intake of whole grains is even more closely associated with mortality and health than a low intake of fruit and vegetables.

To find out what the latest research says about the role of whole grains and cereal fibre in gut health, I recently undertook a review of the literature and discovered some new insights into the unique contribution whole grains and cereal fibres make to our health and wellbeing. 

We’re really only just beginning to understand the complex role the gut microbiome plays in human health, and how food choices may be of benefit, but there are already some clear biological mechanisms linking it with numerous aspects of metabolic, physical and mental health.

The good news is that dietary changes are thought to be responsible for around 57% of the variation in the gut microbiota, so there is a huge potential for diet to modulate the microbiome towards shifts associated with better health outcomes.

Whole grains, cereal fibres and the microbiome

Whole grains contain a distinct combination of cereal fibres and potent phytochemicals that are important for a diverse microbiota and healthy microbiome, which have knock-on benefits for physical and mental health.

One research area has focused on MACs (microbiota-accessible-carbohydrates) a term coined to refer to the fermentable fibres including resistant starch, most soluble fibres, and a smaller percentage of insoluble fibres.

Research shows MACs increase the number and diversity of gut bacteria and provide the prebiotics to feed them. Greater consumption of MACs also leads to increased production of the short chain fatty acids propionate, acetate and butyrate from bacterial fermentation. This helps to regulate appetite, increase absorption of some nutrients and lowers the pH in the lumen, inhibiting the growth of many pathogens.

Insoluble fibres also play a crucial role in carrying MACs through the length of the colon, slowing their fermentation and by doing so, releasing important phytochemicals in areas of the colon that are more prone to cancerous changes. The insoluble fibres also have the highest phenolic content and greatest antioxidant capacity.

This emerging evidence reveals new insights into the benefits of whole grains and cereal fibre and may help explain the association between their consumption and weight management benefits, as well as a lower risk of several chronic diseases, including some cancers (especially colon cancer), type 2 diabetes, obesity and cardiovascular disease (CVD).

More on phytochemicals

Most of the phytochemicals found in whole grains and cereal fibres – in fact 90% of phenolics – are only released through microbial fermentation.

This slow release of phytochemicals can provide longer lasting antioxidant and anti-inflammatory protection and is a unique benefit of diets rich in whole grains and cereal fibres.

As an example, ferulic acid is the most abundant phenolic in whole grains and cereal fibre, particularly whole grain wheat, wheat bran and corn. It is one of the most potent antioxidants found in plant cell walls and may have benefits in preventing and managing various disorders associated with oxidative stress.

Very little of the ferulic acid in whole grains and cereal fibre is directly absorbed because
it is bound to the cereal fibres. Once it reaches the colon, it is gradually released via microbial fermentation. This slow fermentation process keeps levels of ferulic acid elevated in the blood, providing antioxidant protection for up to 24 hours. In contrast, ferulic acid from fruits or drinks, such as coffee, increase blood levels for only 0.5-3 hours.

Many of the antioxidants and other phytochemicals, found in whole grains and cereal fibre are either unique to the grain, such as avenanthramides in oats, or are present in much higher amounts than in any other plant-based foods, as with ferulic acid.

Breakfast cereals and gut health

Regular consumption of whole grain or high fibre breakfast cereals has been shown to have a positive effect on the microbiota and microbiome, with significant changes evident in just three weeks.

For Australians, breakfast cereals are a leading food source of whole grains, cereal fibre and dietary fibre. However, most Australians (70%) still don’t get the recommended 48 grams of whole grains a day. In fact, the median intake for an Aussie adult is only 21 grams a day. For children, the goal is 32-40 grams per day, but their median intake is just 16 grams a day.

Recommendations to consume a bowl a day of whole grain or high cereal fibre breakfast cereal, porridge or muesli, is a cost-effective and convenient means of helping Australians to meet their target intakes for fibre, cereal fibre and whole grains. In fact, the research suggests it is difficult to reach these targets in typical Australian diets without regular consumption of breakfast cereal.

Eating for a healthy gut microbiome

A healthy microbiome is one with a diverse and even mix of different micro-organisms. Here are my tips on eating well for a healthy gut microbiome:

  • Focus on a plant-rich diet, whether or not you choose to also consume animal foods.
  • Include a diversity of plant foods to ensure a diversity of fibres to fuel a diversity of microbes.
  • Choose foods high in wholegrains and cereal fibre daily.
  • Include legumes at least two to three times a week.
  • Try to eat a daily handful of nuts and/or seeds.
  • Eat a variety of different vegetables and fruits each day. 

Dr McMillan conducted a review of the scientific literature on whole grains, cereal fibre and the microbiome, published in the report: ‘The Guts of It: Latest evidence on the critical role of whole grains and cereal fibre for a healthy gut microbiome’. The review and report was funded by a grant from the Australian Breakfast Cereal Manufacturers Forum (ABCMF). 

Always get the best advice

This information is provided for health and nutrition professionals review. It is not a substitute for medical advice. A trusted medical advisor and an Accredited Practising Dietitian provide personalised health and nutrition advice.

September 2019

Dr Joanna Dr Joanna McMillan is one of Australia’s most trusted health and wellbeing experts and a regular commentator on television, radio and in print media. Born and raised in Scotland, Joanna emigrated to Australia in 1999. She is a PhD qualified nutrition scientist, an Accredited Practising Dietitian, Adjunct Senior Research Fellow at La Trobe University and a former fitness instructor, giving her unique credentials to help us all make our way through the increasingly confusing nutrition and health messages in the media.

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