The insight could pave the way for fecal transplants of bacteria to help people manage their weight, reduce their risk of certain metabolic diseases or, more simply, encourage them to broaden the bacteria found in their gut -- and therefore their poop -- by eating a healthier, more varied diet.
"We wanted to characterize how the microbiome changes in obese people ... and see which bacteria live in the gut," said Michelle Beaumont,
a research associate in gut microbiome and obesity at Kings College London, and lead author of the study. "This study has shown a clear link between bacterial diversity in feces and markers of obesity and cardiovascular risk."
Beaumont and her team examined stool samples from more than 1,300 sets of twins taking part in the TwinsUK study, the largest twin registry in the UK for the study of aging-related diseases.
DNA was extracted from the twins' samples to identify what fecal microbes were present. The researchers were eager to see the diversity of microbes rather than the volume, and the types of bacteria found were compared between lean and obese twins to spot any differences in gut flora.
When comparing samples, the team used six measures of obesity, including body-mass index, upper to lower body fat ratios and measurements of visceral fat, a form of fat typically found around important organs in the abdomen.
The greatest difference in the types of microbes was seen when comparing visceral fat. People with lower levels of visceral fat, or leaner people, had a more diverse range of bacteria in their feces. Greater fat levels were equally associated with a lower diversity of bacteria, according to the study, published in the journal Genome biology
"Visceral fat is one of the fats that's hardest to remove," Beaumont said, adding that the amount of this fat usually is proportional to weight. "(It) has a much stronger association with the microbiome than BMI."
Influenced by diet?
The team stresses that this is an association and that they cannot state that the differences in bacteria cause people to be more or less obese.
"At the moment, we cannot say anything about causality," Beaumont said. "It could be the diet that's influencing this."