According to them, food craving is not simply hunger -- in fact, it occurs for a variety of reasons like evolution; psychological factors such as stress, anxiety and unhappiness; and sometimes a genuine need for certain foods.

"Cravings are an overwhelming sensation of desire for a certain food. There are a number of chemicals in the brain that are associated with this."

"First, there is dopamine, a brain chemical that's involved in learning and concentration. When we experience something new, dopamine is released."

"This works in tandem with other brain chemicals called opioids, which give feelings of enjoyment. The combination of these factors mean the brain associates certain activities with pleasure , and it teaches us to do them again and again," Leigh Gibson of Roehampton University said.

Then, experts say, from an evolutionary point of view, junk food cravings are linked to prehistoric times when the brain's opioids and dopamine reacted to the benefit of high-calorie food as a survival mechanism.

"We are programmed to enjoy eating fatty and sugary substances, and our brains tell us to seek them out. Today, we still have the same chemical reactions to these foods," he said.

From the May 2, 2011, Prepared Foods' Daily News.