A new study has revealed a person's appetite can be affected by their state of mind.

Dr. Richard O'Neill explained the study where people were given a 380 calorie milkshake. Some people were told the shake actually contained 620 calories, while others were told it only had 140 calories.

The study focused on the "hunger hormone," which affects hunger level.

The study found that people who were told they were drinking the higher-calorie milkshake had a steep decline in hunger level, while those who were told they had the lower-calorie shake had normal levels of hunger drop off.

To read about the study, click here.