The idea is supported by a study of mice and gut bacteria.

A recent study showed gut microbes present in a diet with fish oil, once transplanted, protected mice on diets rich in lard against weight gain and inflammation normally associated with diets that include unhealthy fats.

"We were surprised that the lard and the fish oil diet, despite having the same energy content and the same amount of dietary fiber--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," study author Robert Caesar said.

"Our paper supports previous reports indicating the bacteria Akkermansia muciniphila is a promoter of a healthy phenotype," senior study author Fredrik Bäckhed said.

But Bäckhed said it’s not yet known if the bacteria “can be used as probiotic strain and, in that case, how it should be combined with diet to optimize health outcomes."