Different bodies respond differently to the same diet and each of us have our own personal mix of bacteria that live in our intestines.
Which bacteria those are could make a difference as researchers attempt to answer the question of why some people are obese and others are not.
Experts believe a number of environmental and genetic factors lead to obesity.
But, scientists at the University of Maryland School of Medicine, have identified 26 different types of bacteria in the human digestive system that appear to be linked to obesity.
They believe these bacteria could cause a condition known as, metabolic syndrome which is made up of different factors that increase the risk of heart problems and diabetes.
"They include elevated cholesterol levels, elevated serum triglycerides levels, high fasting glucose levels, insulin resistance, high blood pressure," said Doctor Claire M. Fraser from the Institute for Genome Sciences at the University of Maryland.
Humans pick up bacteria from the environment, starting with the journey down the birth canal.
This field of study is growing by leaps and bounds thanks to advances in DNA sequencing
Scientists say there is an apparent link between bacteria in the gut and inflammation, a major factor in obesity and other chronic diseases.