The findings from research in mice suggest that diets rich in beneficial omega-3 fats such as fish oil produce a different balance of bacteria in the gut microbiome than a diet rich lard.
Led by senior researcher Professor Fredrik Bäckhed from the University of Gothenburg, the team of European researchers also showed that the changes in gut microbiota make up caused by the dietary fats share some of the responsibility for their health effects.
"We wanted to determine whether gut microbes directly contribute to the metabolic differences associated with diets rich in healthy and unhealthy fats," explained study first author Robert Caesar, also of the University of Gothenburg.
“The study establishes the gut microbiota as an independent factor aggravating inflammation during diet-induced obesity and, therefore, a suitable target for therapies against associated metabolic perturbations,” said the team, who noted that it may be possible that a probiotic supplementation could counteract the effects of a ‘greasy diet’.
Writing in the journal Cell Metabolism, the team began by feeding either lard or fish oil to mice for 11 weeks and monitoring signs of metabolic health.
Bäckhed and his colleagues found that the type of dietary fat is a major driver of community structure, affecting both the composition and diversity of the gut microbiota.
Results from 454 pyrosequencing and qPCR showed that mice fed fish oil had increased levels of taxa from the genera Lactobacillus, and Akkermansia muciniphila, known to reduce weight gain and improve glucose metabolism in mice - while the consumption of lard promoted the growth of bacteria called Bilophila, which have been linked to gut inflammation.
In addition, mice fed lard for 11 weeks were reported to have increased Toll-like receptor (TLR) activation and white adipose tissue (WAT) inflammation and reduced insulin sensitivity compared with mice fed fish oil – with the team noting that phenotypic differences between the dietary groups can be partly attributed to differences in microbiota composition.
"We were surprised that the lard and the fish oil diet, despite having the same energy content and the same amount of dietary fibre - which is the primary energy source for the gut bacteria - resulted in fundamentally different gut microbiota communities and that the microbiota per se had such large effects on health," said Caesar.
In a further set of experiments, the team then transplanted the microbiome of the mice fed either fish oil or lard in to antibiotic-treated mice that were then fed a lard diet for 3 weeks, in order to test whether the changes in microbiota caused by the different dietary fats had any effect on adiposity and inflammation from a lard-rich diet.
“We found that the enrichment of Akkermansia co-occurred with partial protection against adiposity and inflammation in mice transplanted with fish-oil microbiota and fed a lard diet, highlighting Akkermansia as a potential mediator of the improved inflammatory and metabolic phenotype of mice fed fish oil,” said the team.
"Our paper supports previous reports indicating the bacteria Akkermansia muciniphila is a promoter of a healthy phenotype," added Bäckhed.
"However, further investigations will be needed to determine if this bacteria can be used as probiotic strain and, in that case, how it should be combined with diet to optimize health outcomes."