Why don't we crave broccoli?

Katrina Purcell is a researcher who studies factors that contribute to people achieving or not achieving their weight loss targets.

“It‘s interesting how psychological factors can play a role in our appetite regulation,” Dr Purcell says.

“People who have been told they can't eat broccoli crave it! These people include those who are on warfarin and can't consume broccoli due to the high levels of vitamin K, which can interfere with warfarin’s effectiveness in preventing blood clotting.”

The temptation of the forbidden apple, broccoli or the sweet treat is akin to what psychologists call the ‘ironic processing theory’ where active suppressing of a thought only brings it to mind. The current trend in diets is to de-demonise treat foods and reframe them as an ‘okay to have occasionally at special events’ food. 

Cravings are different from real hunger. Science has shown that eating something sweet or sugary actually makes you ‘feel good’ because it affects endorphins and increases serotonin and dopamine levels in your brain. Humans are evolutionarily hardwired to crave these high calorie foods.

“If we craved low calorie foods, we would not be here today,” Dr Purcell explains.

“Animals that evolved to like ripe fruit, which has higher sugar content than unripe fruit, had more energy and this increased their chances of survival and reproduction. Sugar provides not just energy, but it helps store fat. Sugar is broken down to glucose for quick energy when required or stored as fat. In prehistoric times our ancestors may have faced periods when food was in short supply so having a better capacity to store fat helped survival.”

Emotions and memories also drive food cravings. We’ve all had the odd occasion when we yearn for a healthy bowl of grandma’s homemade vegetable soup and other family comfort foods and especially sugary treats. We crave these reward foods that were given to us as children as a gesture of love or reward. 

Moods like being stressed or bored can also trigger a preference for the not-so-healthy options. So can we curb craving by tricking our minds and bodies?

Katrina Purcell suggests a few options. 

“Exercising, drinking water or having a caffeinated drink can curb cravings in the short term,” she says. “All of these have been shown to decrease appetite. And exercise actually stimulates brain chemicals that will improve your mood.”

 Katrina Purcell is a dietitian who has been working with University of Melbourne’s Professor Joseph Proietto, Head of the Weight Control Clinic at Austin Health, on a study that found substantial weight loss is more likely to be achieved if weight is lost quickly. 

Their recent paper suggested a number of possible explanations for their findings including that the limited carbohydrate intake of very-low-calorie diets promotes greater satiety, and less food intake by inducing the production of hunger suppressants called ketones. 

Losing weight quickly may also motivate participants to stick to the diet.