Ever wondered why the more burgers, chips or chocolate you eat, the more you seem to want? It's because food that's high in calories really is addictive.
According to research, eating junk food floods the brain's reward system with the feel-good chemical, dopamine, the surge producing a euphoric effect and encouraging us to want more.
In experiments where mice were fed sweetened, high-fat foods over a 24-hour period, their dopamine levels rose, leading them to seek out more food.
However, scientists discovered when they injected insulin into the pleasure centre of the animals' brains - known as the ventral tegmental area - the mice experienced a drop in appetite.
Published in Proceedings of the National Academy of Sciences, it's believed the findings could also apply to humans.
Dr Stephanie Borgland, of Calgary University in Canada, explained that living in an environment "rich with easily accessible, low-cost, palatable food, this plasticity may be a significant driver of overeating".
She told the Daily Mail the data indicates "mice have increased food approach behaviours and consumption two days after the 24-hour access to the sugary and fatty food."
How does dopamine work?
Dopamine acts on the areas of the brain that regulate movement, emotion, motivation and pleasure.
When these regions are activated at regular levels the system rewards our natural behaviours.
It's when the system is overstimulated that a euphoric effect is created, and prompts the urge to repeat the stimulating action.
Dr Borgland said when we live in places that offer such easy access to "highly palatable and energy dense food" we are driven to seek food "regardless of satiety". It's an effect that can lead to obesity.
But she said insulin, which controls blood sugar levels and helps you feel full after eating, can reduce consumption.
"Targeting this circuit with brain delivered insulin may provide a strategy to suppress food cravings."
As addictive as cocaine
Research has previously shown that fatty or sugar-filled foods can be as addictive as cocaine.
In studies, obese and compulsive eaters were drawn to images of junk food in the same way as cocaine addicts when they were shown bags of the drug.
For the junk food eaters, the decision-making part of their brain was shown to release a surge of dopamine when they looked at unhealthy dishes - the same reaction drug users have when presented with cocaine.