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Food waste is a huge problem all around the world, especially in developed countries. In the US, for instance, about 40% of food in the United States is essentially thrown away, whereas globally, 1.3 billion tons get wasted every year — roughly one third of the total production. Sometimes, however, being mindful not to waste food can lead to overeating, researchers warn.

In many households, parents encourage their children to ‘clean their plates’ — that is, to eat all the food on the plate. While there’s a lot o merit to this attitude, a ‘clean plate’ mentality may actually do more harm and than good in today’s age when calories are abundant and cheaper than ever.

Writing in the journal Appetite, researchers at Vanderbilt University note that people have the tendency to engage in ‘consumption closure’ — a state characterized by perceiving a given eating occasion as finished or complete. In other words, leaving those leftovers on the plate triggers an uneasy psychological state that can be dismissed by cleaning the plate. What’s more, experiments carried out by the researchers revealed that individuals tend to justify their behavior by ‘healthifying’ — essentially downplaying the negative health effects of extra food.

“Many of us were raised with this ‘clean your plate’ mentality, stemming from a desire to ensure one is not being wasteful or their children are eating well; however, this can also lead to overconsumption,” said Kelly Haws, Vanderbilt marketing professor and lead author of the new study. “So, one could argue that good advice for someone trying to manage their food intake would be not to clean their plate.”

We often lie to ourselves to satisfy ‘consumption closure’

The research team performed four studies that explored what happens inside the brain when people have to decide whether or not they should continue consuming.

Haws and colleagues first asked participants to eat a variety of unhealthy foods, such as cookies, chocolate-covered almonds, and pizza. Later, the participants were interviewed about how hungry they were before the meal, how much more they wanted to eat, and how healthy they believed each food was.

During one interesting experiment, the participants had to eat three cookies from plates of a varying number of cookies. When there were only one or two cookies left on the plate, the participants were far more likely to have a go compared to situations when there were more cookies left over. It’s possible, the researchers theorize, that the last cookie is always tempting because we don’t view it as a full serving size, so “one more can’t hurt.”

In another experiment, participants had to imagine that they were eating cookies directly from a package, leaving 1, 3, or 6 cookies behind. When there was only one cookie left in the product’s package, participants were far more likely to eat the last cookie than store it for later.

The ‘last cookie’ also triggers some interesting psychological effects in which we rationalize or justify unhealthy behavior by perceiving it as less damaging. For instance, those who were tempted to eat another cookie tended to underestimate how unhealthy it was. Similarly, those who said they would eat the last cookie also anticipated the greatest satisfaction from it. The last cookie also seems to taste better.

So, if overeating is bad and food waste is bad, what’s the best thing we should do? The researchers found that when participants were offered the option to take their last slices of pizza home, they were less likely to clean their plates. When takeaway wasn’t available, the participants were more likely to be tempted by the last slices of pizza but also to downplay how unhealthy it was.

In conclusion, having a takeaway bag (or asking for one) can be a nifty trick which you can utilize to satisfy consumption closure. Especially this time of year, you should take your leftovers to go.