Benefits of high-fibre diet may depend on gut bacteria

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A high-fibre Nordic diet may only be effective for losing weight if certain bacteria are present in the gut, say Danish researchers, but manufacturers should still add fibre to processed food thanks to its many other health benefits.

Ingredients local to Nordic countries, such as cabbage, fish, wild native berries, oats and rye are high in the Nordic Diet but they do not form the basis of the everyday contemporary Danish diet. This is characterised by an increasing amount of processed food that is low in fibre, fresh fruit and vegetables.

This trend has been linked to rising obesity rates in Scandinavian countries, prompting calls for a return to traditional eating habits to counter this. However, Danish researchers have found that the efficacy of the high-fibre diet may be significantly impacted by gut bacteria, with the Nordic diet only beneficial for weight-loss for those who had plenty of Prevotella bacteria.

But the findings are not a blow for the high-fibre health message.

Mads Fiil Hjorth, assistant professor at the University of Copenhagen’s department of nutrition, exercise and sports and co-author, told us: “Fibre has in general been associated with other health benefits. Therefore, we are not putting restrictions on the intake of dietary fibre for anyone but just highlighting the importance of dietary fibre among half the population.

“[Our findings] mean that approximately half of the population should strive to eat more fibre in their diet. As it for some might be difficult to achieve this relatively high dose without having to change most of their dietary habits it would be relevant for the food industry to add more dietary fibres to processed foods.”      

The study

A total of 62 overweight individuals took part in the study, which was funded by Gelesis, a biotechnology firm which sells a drug to treat obesity and diabetes, with 31 following a ‘New Nordic Diet’ and 23 people following an ‘Average Danish Diet’ for 26 weeks.

As well as taking height and weight measurements, the researchers collected stool samples at the start of the experiment and analysed the microbiota content.

According to the researchers, Bacteroides-driven enterotype tends to be more predominant in individuals consuming more protein and animal fat (typical in a Western diet), whereas the Prevotella-driven enterotype appears to be predominant among people who eat more carbohydrate and fibre.

At the end of the 26 weeks, the Nordic dieters came out top for weight loss, losing an average of 3.5 kilograms, compared to 1.7 kg for the Average Danish Diet. However, the New Nordic Diet worked best for those who had high levels of Prevotella.

They lost 3.15 kilograms more body fat when they followed the New Nordic Diet compared to the Average Danish Diet. Their waistlines also decreased more significantly, and their weight loss was maintained after following the diet for one year. However, the type of diet followed had no influence on how much weight participants in the low ratio group lost.

"These results are a breakthrough demonstrating that certain bacterial species play a decisive role in weight regulation and weight loss," said lead-author and professor at the University of Copenhagen Arne Astrup. "Now we can explain why a high fibre diet does not always lead to weight loss. Human intestinal bacteria is an important part of the answer and will from now on play a role in the treatment of the overweight.”

Source: International Journal of Obesity

“Pre-treatment microbial Prevotella-to-Bacteroides ratio, determines body fat loss success during a 6-month randomized controlled diet intervention”

Article available online 8 September 2017, doi: 10.1038/ijo.2017.220.

Authors: M. Hjorth, H. Roager, T. Larsen, S. Poulsen, T. Licht, M. Bahl, Y. Zohar and A. Astrup

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