Your thoughts can easily fool your stomach -- a new study claims that metabolism speeds up when people believe they are consuming something very indulgent and high in calories, regardless of what the product actually is.

Alia Crum, a psychologist at Columbia Business School, conducted the Milkshake Study to find out the effect of reading calorie labels on the body. She measured the levels of the "hunger hormone" called ghrelin, before and after a group of people drank some milkshake.

Crum distributed each participant the same 380-calorie milkshake: half of them were labeled as containing 620 calories, while the other half were said to contain only 140 calories. As a result, she discovered that the ghrelin levels of the people who drank "high-calorie" milkshake dropped three times as quickly as those of the people who thought they were drinking "low-calorie" milkshake. The hormone not only makes people feel hunger, but also influences the speed of metabolism.

It was previously believed that the ghrelin levels were controlled by the consumed nutrients, and that people become hungry when the levels rise, while metabolism increases when levels of the hormone fall, burning calories. However, the study suggests that there is a placebo effect. In other words, it is not just actual calorie intake, but also perceived calorie consumption that affects the body's level of the hormone and the rate of metabolism.

So what is the best way to lose weight? Crum suggests that people should eat something that is very low in calories but which is believed to be high in calories.