But now a new study is showing that, like drugs and alcohol, some people just can't say no.
"There's no doubt that specific components of our food supply, in particular, the big one is sugar, clearly affect the brain in ways that morphine, nicotine, cocaine, cannabis, ethanol all do as well," says Dr. Robert Lustig, of the University of California, San Francisco.
Dr. Robert Lustig and researchers are looking at how processed foods trigger dopamine receptors in the brain that cause the body to become physically addicted.
According to Lustig, there are four criteria for addiction in humans: Binging, withdrawal, craving and cross sensitization of other drugs of abuse.
He believes that you see all four of these factors when the body is given refined sugar.
A test done on animals, found that they did not over-eat when given their natural diet, but researchers found that the animals gorged themselves until all the cookies were gone.
The same was true when the animals were given Fruit Loops.
Christina Morrison has battled with her weight most of her life.
"I grew up with 'clean your plate, eat everything on your plate,'" said Morrison. "You come home after a long day at work and I'm like, 'I just want a glass of wine and some cheese,' and I may not necessarily be hungry for that."
After participating in a blind study at UCSF, Morrison has lost 30 pounds and kept it off.
She has learned to recognize her food habits and only eat when she's hungry. She's also more aware of how her body reacts to sweets.
"I think when I drink Diet Coke, it makes me want a cookie, like they kinda go together. It's weird" said Morrison.
Not weird, according to Dr. Lustig. Rather it's a chemical reaction.
"If you ask me, I think almost all of it is actually biochemical and there are specific biochemicals that are driving obesity."