Future microbiome research and therapy will have to take into account that diet affects the gut microbes of men and women differently. From Science Daily:
The microbes living in the guts of males and females react differently to diet, even when the diets are identical, according to a new study. These results suggest that therapies designed to improve human health and treat diseases through nutrition might need to be tailored for each sex.
The researchers studied the gut microbes in two species of fish and in mice, and also conducted an in-depth analysis of data that other researchers collected on humans. They found that in fish and humans diet affected the microbiota of males and females differently. In some cases, different species of microbes would dominate, while in others, the diversity of bacteria would be higher in one sex than the other.
These results suggest that any therapies designed to improve human health through diet should take into account whether the patient is male or female.
Genetics and diet can affect the variety and number of these microbes in the human gut, which can in turn have a profound influence on human health. Obesity, diabetes, and inflammatory bowel disease have all been linked to low diversity of bacteria in the human gut.
Why men and women would react differently to changes in diet is unclear, but there are a couple of possibilities. The hormones associated with each sex could potentially influence gut microbes, favoring one strain over another. Also, the sexes often differ in how their immune systems function, which could affect which microbes live and die in the microbiome.
One notable exception in Bolnick's results was in the mice. Although there was a tiny difference between male and female mice, for the most part the microbiota of each sex reacted to diet in the same manner. Because most dietary studies are conducted on mice, this result could have a huge effect on such research, and it raises questions about how well studies of gut microbes in lab mice can be generalized to other species, particularly humans.