A laboratory claims to have made a breakthrough in the search for obesity treatment.
Researchers at Brookhaven National Laboratory (BNL) used an expandable balloon in volunteers' stomachs to test brain function.
Gene-Jack Wang of BNLs Translational Neuroimaging centre said that the results revealed people who were overweight were less likely to be told by their brains that they had eaten enough.
"By simulating feelings of fullness with an expandable balloon we saw the activation of different areas of the brain in normal weight and overweight people," he said.
"These findings provide new evidence for why some people will continue to eat despite having eaten a moderate-size meal."
The balloons were swallowed by participants and varying amounts of water were used to inflate it while researchers used functional magnetic resonance imaging to monitor corresponding brain activity.
BNL is run by the US department of Energy.
The NHS describes obesity as being when a person's body fat is too much for their height and sex and if they have a body mass index of 30 or more.