The search for the most successful way to shed the pounds seems never-ending.
Now researchers in China have looked at what impact gut bacteria have on people's weight.
They think that changing the type of bacteria found in the gut may be more effective at helping people to shed weight than cutting calories alone.
But can it really be as simple as that?
Experts warn we shouldn't ditch the cucumber sticks and hot yoga just yet.
The latest World Health Organization figures show there were more than 1.4 billion adults aged 20 or older who were overweight in 2008.
Of these, 200 million men and nearly 300 million women were obese.
Those numbers are rising - they have doubled since 1980.
Lab tests in mice found an association between bacteria and obesity, but trials with people are only just getting started.
In a clinical trial, published in the journal Microbiology Ecology, scientists in Shanghai studied 93 obese people who started with an average Body Mass Index (BMI) of 32.
They fed the volunteers supplements that promoted the growth of certain types of bacteria and reduced the levels of other bacteria in the gut, alongside a balanced diet.