There's a reason people buy single-serving snacks: when presented with a giant bag of things that are tasty, it's hard to both keep track of how much you've eaten and convince yourself that no, you really don't need to eat just one more. Researchers from Cornell's Food and Brand Lab may have a solution: adding "stop signs" to food.
In a study published this month in Health Psychology, researchers presented tubes of Lay's Stackables (i.e. Pringles) to a group of about a hundred undergraduates while they were watching videos in class. Unbeknownst to the students, some of the tubes of chips had been tampered with, and included chips that had been dyed red interspersed with regular chips at intervals corresponding to either one or two serving sizes.
The students noticed the red chips, of course, but even though they didn't know why the chips were red, they still changed their eating behavior significantly, consuming about 50% fewer chips than students eating non-dyed control group chips. Furthermore, the dyed chips also helped students later estimate how much they'd eaten: while the control group underestimated their total chip consumption by an average of 13 chips (nearly two servings), students eating dyed chips were able to remember accurately within just one chip.
What's really cool about this experiment is that none of the students were told how much to eat or when to stop. It simply turned out that including a visual indication of serving size caused people to eat fewer chips, reducing caloric intake by about 250 calories. You can call these edible "stop signs" subconscious if you like, but the fact that such a simple change can prompt people to voluntarily eat less is remarkable.
This research has significant implications for public health (and follow-up research is already planned to investigate the concept further), it's just going to have to withstand what's sure to be very aggressive lobbying from the snack food industry: as it turns out, maybe you can eat just one.