The recent study challenges the theory that animal protein intake and a compromised metabolic status might also be accompanied by a decrease in gut microbiota.
Researchers are closer to completing the jigsaw, but are still puzzling over the precise biological mechanism that is responsible for the link between animal protein intake and the development of type 2 diabetes.
“In both cohorts, animal (but not plant) protein intake was associated with pre-type 2 diabetes and type 2 diabetes status…There was no significant association between protein intake with either gut microbiota alpha diversity or beta diversity, regardless of ethnicity,” wrote the researchers in the journal 'Nutrients'.
However, at the species level, the researchers identified gut microbial taxonomical signatures, which they said could function as potential modulators in the association between dietary protein intake and metabolic status.
“We reported several species associated with animal protein intake, which could serve as potential targets for future studies,” they wrote.
Multiple studies have shown that the gut microbiota composition and function of patients with type-2 diabetes is altered compared with healthy individuals. This alteration is mainly characterised by a decrease in diversity, which is attributed to the production of deleterious gut derived metabolites, such as branch chained amino acids (BCAA) and trimethylamines (TMA).
Diet is one of the main modulators of metabolic status (eg insulin resistance) as well as gut microbiota composition and function. Animal protein has been found to be associated with a higher risk of type-2 diabetes compared to plant protein. Dietary protein is also linked to the production of the above mentioned metabolites, which can increase insulin resistance via the gut microbiota.
The aim of this study was to investigate the interaction between dietary protein, the gut microbiota and metabolic status in two large cohorts from different European countries.
The researchers examined 1759 subjects from the MetaCardis cohort and 1549 from the Healthy Life in an Urban Setting (HELIUS) cohort. For the MetaCardis cohort, subjects were recruited from France, Germany and Denmark. The HELIUS subjects were recruited from Amsterdam and Holland. Data was obtained via food frequency questionnaires and gut microbiota composition.
Exploring microbiota diversity and macronutrient intake
Being a high protein eater was strongly associated with type 2 diabetes and pre-type 2 diabetes in both cohorts. In the MetaCardis cohort, the researchers observed that the association between animal protein intake and type 2 diabetes was more pronounced in Caucasians than non-Caucasians, however this was not the case in the other cohort.
The researchers then determined the links between alpha diversity and macronutrient intake. In both cohorts, unsaturated fat intake was positively associated with alpha diversity, while carbohydrate intake was negatively associated with alpha diversity. In contrast, there was no correlation between protein intake and alpha diversity.
Examining the link between beta diversity and macronutrient intake the researchers found that dietary fibre and plant protein were significantly associated with beta diversity, whereas animal protein was not.
“Overall…protein and specifically animal protein intake were not significantly linked with gut microbial beta diversity in our two cohorts, regardless of Caucasian vs non-Caucasian ethnicity,” wrote the researchers.
Since animal protein intake was linked with type 2 diabetes status but not gut microbiota diversity, the researchers sought to identify whether specific microbial species were associated with animal protein consumption.
Among the 30 most important species associated with animal protein intake, 11 were common to both cohorts. Most of these were positively associated with animal protein intake apart from Roseburia hominis, which showed a negative association. Interestingly, this bacteria strain has been identified as a major butyrate producer, which is associated with improved metabolic status. The closely associated Roseburia inulivorans, on the other hand, was positively associated with animal protein intake.
“This finding highlights the diverse effects of protein intake on bacterial species, warranting further studies in order to modulate metabolic status,” wrote the researchers.
For eight of the species, abundance was significantly associated with ethnicity, with the majority being more abundant in Caucasians.
“This increase in animal protein-associated bacteria could perhaps contribute to the more pronounced association of animal protein intake observed in Caucasians…This finding again highlights the importance of an ethnic specific approach to gut microbiota research,” they wrote.
They said future studies with well characterised ethnic groups, in-depth microbiota sequencing techniques and detailed dietary data were needed to shed further light on the complex interplay between diet, health and the gut microbiota.
Bel Lassen P, Attaye I, Adriouch S, Nicolaou M, Aron-Wisnewsky J, Nielsen T, Chakaroun R, Le Chatelier E, Forslund S, Belda E, Bork P, Bäckhed F, Stumvoll M, Pedersen O, Herrema H, Groen AK, Pinto-Sietsma S-J, Zwinderman AH, Nieuwdorp M, Clement K, on behalf of Metacardis Consortium.
“Protein intake, metabolic status and the gut microbiota in different ethnicities: results from two independent cohorts”