That a Mediterranean diet might protect against breast cancer has been suggested by several human studies. Now, Shively and co-workers provide evidence that the mammary gland microbiome might form part of the explanation.

Female macaque monkeys were fed either a Western diet or a Mediterranean diet for 31 months. The Western diet was low in fibre, high in sucrose and high in animal fats. The Mediterranean diet had a higher fibre content and lower sucrose, and olive oil was the chief source of dietary fat.

Mammary gland tissue was then analysed to characterise its microbiome and metabolome. Compared with a Western diet, monkeys fed a Mediterranean diet had a 10-fold higher prevalence of Lactobacillus. They had a lower abundance of Ruminococcus and Lachnospiraceae bacteria. Metabolomic analyses demonstrated a reduction in metabolites associated with oxidative stress and inflammation in the Mediterranean diet cohort. Some of these beneficial metabolites are those which have undergone bacterial processing (from tryptophan into indole products, for example).

The authors therefore suggest that the microbiome might contribute to the mechanism by which diet influences breast cancer risk.

Read the full article in Cell Reports 25 47‒56