A new study has found that junk food can be addictive, even when the person eating it knows it is bad for them.
Neurobiologist Associate Professor Paul Kenny from the Scripps Research Institute in Florida, and co-author of a paper published in Nature Neuroscience, says overeating junk food can lead to a compulsive habit.
Kenny, along with colleague Paul Johnson, tested the theory with laboratory rats, and found disturbing similarities with the way drugs collapse the brain's reward pathways by over-stimulating them.
"As a result the reward pathways become hypo-functional, they just don't work as well. And because of that we think that may drive further and further drug use," says Kenny.
"The second hallmark of excessive drug use is the fact your behaviour directed towards them can become very compulsive and inflexible.
"In other words, it almost becomes beyond your control, and you'll keep on taking the drug even when really you shouldn't."
Kenny says his study supports what people have intuitively known for a long time, that food can have addiction-like properties.
Challenge for society
He says the challenge in modern society is to try and remove temptation when it can be found almost anywhere.
Australian obesity expert Professor Boyd Swinburn from Deakin University in Melbourne agrees.
He says in the past 30 years, across the globe, there has been a revolution in the food environment.
"The products have become much more processed and manufactured and therefore energy-dense, and they worked out what things to add like sugar, salt and fat and a whole bunch of other chemicals to make it tasty," says Swinburn.
"So the food itself has changed enormously. The price has also come down in relative terms over the decade.
"The placement has just expanded enormously so food is absolutely everywhere that you turn.
"And of course the promotion and the marketing of food have changed to become much more sophisticated that it was thirty years ago."
Stand out examples
Swinburn says Japan, South Korea and some Scandinavian countries stand out as advanced economies where obesity has not grown with individual wealth.
In the case of Asia he puts that down to maintaining traditional cuisine and resisting the lure of junk food.
In Europe credit is given to a culture which embraces more active transport, including riding to work and school.