The secret to eating less and being happy about it may have been cracked years ago-by McDonald’s. According to a new study from Cornell University’s Food and Brand Lab, small non-food rewards-like the toys in McDonald’s Happy Meals-stimulate the same reward centers in the brain as food does.

The researchers, led by Martin Reimann, carried out a series of experiments to see if people would choose a smaller meal if it was paired with a non-food item.

They found that the majority of both kids and adults opted for a half-sized portion when combined with a prize. Both options were priced the same.

Even more interesting is that the promise of a future reward was enough to make adults choose the s maller portion. One of the prizes used was a lottery ticket (彩票), with a $10, $50 or $100 payout, and this was as effective as a tangible gift in persuading people to eat less.

“The fact that participants were willing to substitute part of a food item for the mere prospect of a relatively small monetary award is interesting,” says Reimann.

He theorizes that it is the emotional component of these intangible prizes that make them effective. In fact, vaguely-stated possibilities of winning a prize were more effective than options with hard odds included.

“One explanation for this finding is that possible awards may be more emotionally provoking than certainty awards,” says Reimann. “The uncertainty of winning provides added attraction and desirability through emotional ‘thrills’. The possibility of receiving an award also produces a state of hope-a state that is in itself psychologically rewarding.” In other words, there’s a reason why people like to gamble.

How might this knowledge be used to help people eat more healthily?

One possibility is a healthy option that offers the chance to win a spa (温泉疗养) weekend. Or maybe the reward of a half-sized portion could be a half-sized dessert to be claimed only on a future date. That would get you back in the restaurant-and make you eat a little less.