OBJECTIVE: Individuals with obesity and type 2 diabetes differ from lean and 
healthy individuals in their abundance of certain gut microbial species and 
microbial gene richness. Abundance of Akkermansia muciniphila, a mucin-degrading 
bacterium, has been inversely associated with body fat mass and glucose 
intolerance in mice, but more evidence is needed in humans. The impact of diet 
and weight loss on this bacterial species is unknown. Our objective was to 
evaluate the association between faecal A. muciniphila abundance, faecal 
microbiome gene richness, diet, host characteristics, and their changes after 
calorie restriction (CR).
DESIGN: The intervention consisted of a 6-week CR period followed by a 6-week 
weight stabilisation diet in overweight and obese adults (N=49, including 41 
women). Faecal A. muciniphila abundance, faecal microbial gene richness, diet 
and bioclinical parameters were measured at baseline and after CR and weight 
stabilisation.
RESULTS: At baseline A. muciniphila was inversely related to fasting glucose, 
waist-to-hip ratio and subcutaneous adipocyte diameter. Subjects with higher 
gene richness and A. muciniphila abundance exhibited the healthiest metabolic 
status, particularly in fasting plasma glucose, plasma triglycerides and body 
fat distribution. Individuals with higher baseline A. muciniphila displayed 
greater improvement in insulin sensitivity markers and other clinical parameters 
after CR. These participants also experienced a reduction in A. muciniphila 
abundance, but it remained significantly higher than in individuals with lower 
baseline abundance. A. muciniphila was associated with microbial species known 
to be related to health.
CONCLUSIONS: A. muciniphila is associated with a healthier metabolic status and 
better clinical outcomes after CR in overweight/obese adults. The interaction 
between gut microbiota ecology and A. muciniphila warrants further 
investigation.
TRIAL REGISTRATION NUMBER: NCT01314690.