"The second thing is more insidious. We're pretty bad at deciding how much we are going to eat. We don't know what an appropriate amount is. So we look for some sort of cue as to what would be normal to take. And in the case of jelly beans, if there's a whole lot, it raises the estimate of what you believe is typical for somebody to take. If there's a whole lot of variety there, it's normal for me to take more."
We perceive variety, even if only in color, as meaning there's more available, even if the total number is actually the same. So if there's more there, it's OK to take more, although one of the studies suggested that if we think we might be depriving someone else of jelly beans, we might back off a little. It's not certain yet whether that was because the participants didn't want to eat someone else's candy, or they just didn't want to appear piggish, but the evidence suggests the latter.
There appears to be no limit in how far Wansink will go to understand our metabolic trickery. In one study, he designed a refillable soup bowl. Hidden tubes refilled the bowls so slowly that the participants didn't see it. Women ate 30 percent more soup if they had a refillable bowl than participants who had a regular bowl. Men ate 40 percent more. When asked later how much they thought they had eaten, there was no significant difference between those with, or without, refillable bowls. That suggests that when we are trying to determine how much we have eaten, we may be clueless.
Even the size of the container can make a difference. In one study the researchers gave participants buckets of 14-day-old popcorn. Some were given a large bucket, others a medium bucket. The stuff "tasted terrible," Wansink says, but people with large buckets ate 31 percent more than those with medium buckets, but both groups thought they had eaten about the same.
So where does all this leave us?
If there's more variety available, you'll probably eat more, so don't put a little bit of everything on your plate. Stick to a couple of items. Put the cheesecake where it's out of reach, and pull the broccoli closer. And put your meal in a smaller bucket.
Oh, and beware of jelly beans of many colors.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.