According to obesity researcher, Biochemist and Neurobiologist Stephan Guyenet, cravings have ancestral roots. When we were cavemen, many thousands of years ago, ensuring we had enough calories to survive and reproduce was of paramount importance. We are primed, therefore, to be motivated by foods that have a high reward value. These foods tend to have the highest concentrations of one (or a combination of) sugar, starch, protein, fat, salt and glutamate. However, we now find ourselves in a situation where we can regulate our food intake rather easily. We do not have to hunt and forage for a foods. However, our brains have not evolved at the same pace as our environment. 
Guyenet has termed this an 'evolutionary mismatch'. That is, a situation in which once useful traits become harmful once they're dragged into an unfamiliar environment. 

So why do we crave some foods more than others? Why are Brussels sprouts far less seductive than ice cream, for example?
It appears we have developed a conditioning for foods that deliver the most calories per bite. Flavours and smells are a quick way for the brain to gather information about the nutritional quality of a food before it enters the digestive tract. When we eat foods that deliver the properties we seek, our brain releases dopamine, which drives us to seek the favours, smells, textures, appearances and places we've learned to associate with foods that contain those properties.

Chocolate has been found to be the most craved food in America

Chocolate has been found to be the most craved food in America

As Guyenet explains: -
"As far as the brain is concerned, the fact that Brussels sprouts are loaded with vitamins and minerals counts for approximately nothing, because they are low in calories. In contrast, we crave ice cream because our brains know that its flavour, texture, and appearance predict the delivery of a truckload of easily digested fat and sugar. Having evolved in an era of relative food scarcity, the human brain interprets this as highly desirable and draws us toward the freezer."
The unconscious parts of the brain can drive us to seek out these highly valuable foods, even if we aren't hungry. This is why most of us can eat dessert, even after a large meal.

So what can we do to avoid these cravings? Well the first point to make here is that if someone were looking to quit smoking, they wouldn't leave packets of cigarettes lying around their home or office. In fact, you would do all you can to actively avoid cigarettes, cigarette smells, cigarette advertising etc. Similarly with food it is important to limit what Guyenet calls ‘cue exposure’, such as: 

  • Try to avoid advertisements on TV, magazines etc
  • Controlling home and work food environments

Guyenet also suggests focusing on simple, unrefined foods such as fruits, vegetables, meat, dairy, potatoes, sweet potatoes etc. These foods do not have the high concentrations of nutrients that spike the dopamine response in the brain.

The reward associations that you form with certain foods can be forgotten over time - therefore ‘starve a craving’. Cheat days/meals can re-active a craving for a certain food.