Body mass index may play a role in how the decomposition of the human body affects the soil around it, a new study has shown.

Researchers have looked in more detail at the factors within the body that may have an impact on decomposition, following on from conventional research which looks at environmental factors such as temperature.

The team from the University of Tennessee discovered that in the soil around bodies classed as underweight or a normal weight, the diversity in bacterial communities reduced. This diversity remained virtually constant in the soil surrounding bodies classed as obese or overweight.

What may play a part is that fat and muscle have different chemical properties that could play different roles in the effect on the soil. More fat means more moisture along with a higher ratio of carbon to nitrogen.

Dr Jennifer DeBruyn, a microbial ecologist at the University’s Anthropology Research Facility, said: “We know from plant litter studies that even slight changes in tissue chemistry can change the microbial decomposers.”

The study was launched after researchers noticed that donated bodies differed in how they decomposed, with Dr DeBruyn saying: “The bodies experienced identical environmental conditions, but we saw big differences in how quickly they decomposed.” The observations led the team to suspect that something within the body affected the process.

The study analysed 19 bodies between February 2019 and March 2020, with the donors’ ages ranging from 40 years to 91. Their BMIs ranged from 14.2 to 55.1. Researchers took soil samples and collected fluids released by the bodies during decomposition.

Their findings showed more diversity in the microbe communities in the soil than what they had found in the decomposition fluids.

Dr DeBruyn said: “My PhD student Allison Mason spent so much time digging into the data for any explanation of why we saw the differences we did. And then she stumbled on BMI as a predictor.”

She said further studies are required, adding: “The biggest problem with these humans is that we’re just a big mixed bag of chemicals, and that’s why this kind of study really hasn’t been done before.

“Our paper is really one of the first to use a large enough sample size of donors to reveal these patterns.”

Read the full study in mSphere.

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