The key to weight loss could lie in your gut.
That's according to a new study which shows that some of us have higher levels of a key bacteria that responds to diet and exercise.
The gut is still something of a mystery to even the most accomplished of researchers: we know that it can affect everything from immunity to brain function, and that everyone's personal cocktail of gut bacteria is different, but we are still working out how these types of bacteria work in each person.
According to the Daily Mail, in a significant development, researchers at the Mayo Clinic have shown that some people have much higher levels of an anti-inflammatory bacterium called Phascolarctobacterium - and that it seems to make them more responsive to weight loss.
Co-senior author Dr Purna Kashyap, a gastroenterologist, says the finding suggests we should aim to find a way to screen obese patients' gut bacteria make-up, to see whether it is a gut bacteria issue that is hampering their attempts to get fit.
"We know some people don't lose weight as effectively as others despite reducing caloric consumption and increasing physical activity," Dr Kashyap said.
His team at the Mayo Clinic in Rochester, Minnesota, wondered if there may be other factors at work that prevented these patients from responding to traditional weight-loss strategies.
Dr Vandana Nehra, another senior author on the paper, said: "Gut bacteria have the capacity to break down complex food particles which provides us with additional energy. And this is normally good for us.
"However, for some individuals trying to lose weight, this process may become a hindrance."
The researchers decided to test if certain functions performed by gut bacteria that provide people with more energy may be responsible for the inability of some individuals to lose weight.
They collected and analysed gut bacteria samples from a group of 26 participants enrolled in the Mayo Clinic Obesity Treatment Research Program between August and September 2013.
They found gut bacteria among those who did not lose weight were different from the others.
Specifically, the bacteria Phascolarctobacterium was associated with success, while Dialister was associated with difficulty.
More importantly, the increased ability to use certain carbohydrates was linked with failure.
Dr Kashyap said: "This suggested to us that gut bacteria may possibly be an important determinant of weight loss in response to diet and lifestyle changes."
Dr. Kashyap said more research is required to confirm the preliminary findings published in Mayo Clinic Proceedings.
But he said: "While we need to replicate these findings in a bigger study we now have an important direction to pursue in terms of potentially providing more individualised strategies for people who struggle with obesity."