Is dietary fibre the key to a longer life?

Wednesday, 27 May 2020

Two recent studies from University of Otago researchers have shown eating more dietary fibre improves life expectancy, although food processing may remove these benefits.

About the research

One study using data collected from 8300 adults with type 1 or type 2 diabetes found those with a higher fibre intake had a significant reduction in premature mortality compared to those eating lower levels of fibre.

Lead author Dr Andrew Reynolds says people consuming 35g of fibre per day have a 35% less risk of dying early compared with people who eat 19 grams of fibre per day.

His advice is to increase fibre intakes by eating more wholegrains, legumes, vegetables, and whole fruit applies to people across the globe.

New ways to add fibre

“Try a few different ways to increase your fibre intake, see what works best for you,” Dr Reynolds said.

“If you eat white refined bread or rolls, try changing to wholegrain bread or rolls. Try brown rice, try brown pasta, try adding half a tin of legumes to meals you already make.

“Try an extra vegetable with your main meal – fresh, frozen, or canned without sodium are all good choices.”

The health benefits of fibre

The research team also analysed 42 trials with 1789 participants where adults with prediabetes, type 1 or type 2 diabetes were given more fibre and wholegrains for at least six weeks.

They found consistent improvements in blood glucose control, cholesterol levels and reductions in body weight when adults with prediabetes, type 1 or type 2 diabetes increased their fibre or wholegrain intake.

Senior author Professor Jim Mann has been involved in diabetes research for more than 40 years and led the first controlled trials of high fibre diets in diabetes in the 1970s.

“When our controlled studies confirmed the benefits of dietary fibre four decades ago, we never suspected that they would be quite so impressive,” he says.

“It has taken 40 years of research and these meta analyses to be able to show that this dietary treatment can have an effect as striking as that produced by medications.”

Not all fibre is created equal

In the second study, researchers found not all foods that contain fibre are created equal – while wholegrains are an important source of fibre, their benefits may be diluted when heavily processed.

For this study, Dr Reynolds and Prof. Mann led a trial in adults with type 2 diabetes to consider the effects of food processing on the health benefits of wholegrains.

Participants ate minimally processed wholegrain foods such as wholegrain oats and chunky grainy bread for one fortnight, then more processed wholegrain foods such as instant oats and wholemeal bread for another fortnight.

“Wholegrain foods are now widely perceived to be beneficial, but increasingly products available on the supermarket shelves are ultra-processed,” says Prof. Mann.

Researchers used cutting edge glucose monitors to record participant blood glucose levels over the day and night during the two-week intervention periods.

Results showed improved blood glucose levels after meals and reduced variability of blood glucose levels throughout the day when participants consumed the minimally processed wholegrains.

The results were most striking after breakfast, as that was when most of the wholegrains were consumed.

Something unexpected

Although participants were asked not to lose weight by eating less during the trial, results showed their average weight increased slightly after two weeks of eating processed wholegrains and decreased slightly after eating minimally processed wholegrains.

These two studies, along with previous research, confirm choosing high fibre foods such as wholegrains, whole fruit, dark leafy greens or legumes is good for everyone, and important in managing diseases such as type 1 or type 2 diabetes, explained Dr Reynolds.

“However, we are now beginning to understand that how foods are processed is also important, and for wholegrains when you finely mill them you can remove their benefits,” he concluded.

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