A psychology study published in the Journal of Consumer Research has shown that linking food to purchasing increases impulsive spending.
In the study, two groups of subjects were shown two different sets of photos. One group saw images of nature, while the other, images of food. Both groups then participated in a game in which they had to choose between taking a smaller immediate prize, or a bigger prize after waiting a period of time.
The results-people who viewed the images of food were far more likely to choose the smaller, immediate pleasure.
To test this behavior in a real world environment, researchers hid a cookie-scented candle in a room where female subjects were told to shop. The women were almost five times more likely to buy a new sweater on impulse than female subjects who were in a room without the candle.
This is because until very recently, food was hard to come by, so if we spotted it, we ate it right away. Thousands of years later our brains are still wired to decide that if we wait until later, the reward may be gone.
It seems that seeing, or smelling food primes our brains for immediate reward, altering our behavior.