Why a high-fibre diet doesn’t always lead to weight loss

Research into the human gut microbiota is increasingly playing a role in personalising nutrition. A new study published in the International Journal of Obesity shows why the increasingly popular fibre-rich ‘New Nordic Diet’ won’t work for everyone.

It depends on the particular combination of bacteria in the intestines of the dieter.

A group of 62 overweight participants were randomly assigned to follow either the Nordic diet or an average Danish diet. These eating plans vary greatly in the volume of dietary fibre and wholegrain being consumed. The former is the more fibre-rich option and places greater emphasis on wholefoods such as vegetables and fruits. The participants’ weight and body measurements were taken before and after they started their 26-week diets.

The results of their stool samples were used to divide participants into two different gut bacteria groups. This was done based on the amount of Prevotella bacteria types found in their intestines. About half of the group fell in the high volume group, whereas the other half were placed in the low volume group.

On average, the 31 subjects who ate the Nordic diet for 26 weeks lost 3.5 kilograms, whereas the 23 subjects following the average Danish diet lost 1.7 kilograms. The New Nordic Diet worked best for participants in the high volume Prevotella group. They lost 3.15 kilograms more body fat, and their waistlines also decreased more significantly.

The study’s co-lead author, Arne Astrup, said: ‘These results are a breakthrough demonstrating that certain bacterial species play a decisive role in weight regulation and weight loss. 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.’

‘The health promoting aspects of the New Nordic Diet in terms of body weight regulation seem mainly to apply to a subset of the population. This could apply to as much as half of the population.’