Not adding up: Mental math may equal higher-calorie dining

· 5 min read

Not adding up: Mental math may equal higher-calorie dining

Craig Chandler | University Communication
Christopher Gustafson and a colleague have found that people may subconsciously underestimate the number of calories they order when dining out.

Restaurant-goers could apparently use some help calculating more than just tips.

Those who use mental arithmetic to estimate calorie totals may order higher-calorie meals than patrons who are presented with the hard numbers, says a new study led by the University of Nebraska–Lincoln.

As part of an experiment co-designed by Nebraska’s Christopher Gustafson, 344 people were randomly placed into one of two groups. Both groups ordered sandwiches by selecting from five categories of ingredients: meat, cheese, spread, bread and vegetable.

Members of one group received continual, precise updates on their calorie counts after choosing each ingredient. Though members of the other group also had access to the calories contributed by each ingredient, they had to do the math themselves if they wanted to know their totals.

When Gustafson crunched the data with Eliana Zeballos, a researcher from the U.S. Department of Agriculture’s Economic Research Service, the duo found that the mental-math group ordered sandwiches containing about 5% more calories.

And after comparing the calorie disparities across each category of ingredient, the researchers saw evidence that the mounting calorie information influenced the choices of the hard-numbers group. That group selected meat containing just 2.7 fewer calories, on average, than the mental-math group. But as both groups proceeded to choose cheese, then spread, then bread, those per-category differences rose to 6.3, 7 and then 17.2 calories, respectively.

“It suggests that if there were a way to keep this information relevant for people, the bigger gains might come from the dynamic decision-making component,” said Gustafson, assistant professor in the Department of Agricultural Economics. “If people are getting a more accurate view of the number of calories that they’ve ordered or consumed throughout the day, that might lead them to reduce (caloric intake) or change their behavior later on.”

Gustafson said that’s especially likely to be true when dining out, which often forces people to make multiple decisions within a relatively limited timeframe. Those factors led the researchers to design their experiment around sandwich-building, though the study’s findings may well apply to other restaurant settings, he said.

“Take McDonald’s: sandwich, a side, drink, possibly dessert,” Gustafson said. “You’d have to remember how many calories that hamburger you’ve ordered has, then (calculate) the number that a drink would add to it and that fries would add to it.

“It’s hard to keep all of those things in mind, particularly while your brain is engaged and thinking about the next thing you’re ordering.”

But the study suggests there may be more at play than just this cognitive burden. Gustafson and Zeballos later asked participants from both groups to report how many calories were in the sandwiches they ordered. On average, members of the hard-numbers group — those previously given their actual calorie totals — reported numbers relatively close to what they ordered.

The mental-math group missed the mark more frequently and widely, as would be expected when estimating. Yet some data indicated that participants from the group may have deliberately, if subconsciously, fooled themselves into believing they ordered fewer calories than they actually did.

If random errors and faulty shortcuts were solely to blame, the percentage of underestimates vs. overestimates should have been relatively equal, or at least skewed in ways similar to the hard-numbers group. Instead, roughly 70% of the mental-math group underestimated the total calories, with just 27% overestimating.

On the whole, the mental-math group underestimated its total by an average of about 130 calories — a number that could partly explain the disparity in how many calories the two groups actually ordered, Gustafson said.

“If people are subconsciously or consciously trying to justify their behavior to themselves and leave room to get a cookie afterward — or if they just want to have a better view of themselves — then you would think that they would, as we saw, underestimate the number of calories they’d ordered,” he said.

‘Technology is an interesting frontier’

Over the past few decades, in efforts to curb the obesity epidemic that now afflicts about 40% of its adult population, the United States has enacted policies and initiatives that give consumers better access to calorie information. One of them requires restaurants and retailers with more than 20 locations to post calorie counts on request. Some restaurants now voluntarily post them.

As the new study and others before it have shown, though, making that information salient and easily available seems to be critical, Gustafson said.

“In general, the overarching findings from research on nutrition-facts panels and on calorie labeling in restaurants is that there isn’t much of an effect on behavior from just providing that information to consumers,” he said. “A significant percentage of people don’t even notice that information is there.”

One potential solution: ordering online via websites that automatically calculate calorie totals. A few restaurants, including HuHot Mongolian Grill, already offer the feature in some capacity, Gustafson said.

The study’s findings also make a case for using personalized technology — a calorie-tracking app, for instance — rather than relying on fuzzy or biased math that doesn’t quite add up.

“For people who are interested in losing weight or controlling it, an app or something that they could use when making these ordering decisions could be relevant for this,” Gustafson said. “I think technology is an interesting frontier for helping people make healthier choices.”

Gustafson and Zeballos reported their findings in the journal Appetite.

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