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Finalist for IACP Cookbook Award in Food Matters category, International Association of Culinary Professionals
More Calorie Confusion
Portion Distortion, Health Halos, and Wishful Thinking
For many years Dr. Lisa Young, an expert on portion size and author of The Portion Teller (Crown, 2005), has taught an introductory nutrition class at New York University. As a favor to us, she agreed to devote some time on the first day of class to asking students about their basic understanding of food calories. Among her questions were these: How many calories are in an 8-ounce soda? How many calories are in a 64-ounce Double Gulp soda?
We did not expect beginning students to know the number of calories in an 8-ounce soft drink, and most did not. An 8-ounce soft drink contains about 100 calories. A drink 8 times larger should contain 8 times as many calories-800. Although this is not higher mathematics, only about a quarter of the class correctly multiplied the number they guessed for the size of the smaller drink by 8.
Instead, a large majority of students-nearly 70 percent-underestimated the calories in the larger drink. The underestimaters typically multiplied the calories in the 8-ounce drink by an average of 3, not 8. How could this be? We asked Dr. Young to try to find out from her students why their estimates were so far off. Their answer: 800 calories in a soda is impossible. They simply did not believe the math. Soda package labels, the students pointed out, never say "800 calories"; they say "100 calories per serving." Besides, drinking sodas doesn't make them feel full.
We should not have been surprised. In lectures, we often show a photograph of Dr. Young posed behind soft drink containers ranging from 8 to 64 ounces. When we tell audiences that a 64-ounce soda has 800 calories, we are met with gasps of disbelief-even from trained nutritionists. As we keep pointing out, calories are invisible and devoid of taste. You cannot tell how many are in a food just by looking at it or even tasting it. If you eat anything other than packaged foods with Nutrition Facts labels or anyplace other than fast-food restaurants that post calories on menu boards, you can only guess the number of calories in your foods. If you want to know how many calories you are eating, you have to weigh every ingredient in everything you eat and drink and look up the calories in food composition tables. Even so, these will only be estimates that depend on the accuracy of your weighing. Restaurant calories are particularly difficult because customers have no idea (and are not supposed to know) how the foods were prepared.
This is not because people are ignorant. Even professional nutritionists cannot estimate calories accurately. In the mid-1990s Marion Nestle and Lisa Young demonstrated this embarrassing fact when they were invited by New York Times reporter Marian Burros to lunch at a fine Italian restaurant in company with some other nutrition educators. Burros ordered two of everything on the menu. She asked the nutritionists to guess the calories in one set of meals and sent the matching meals off to a laboratory to be analyzed. Not one of the nutritionists came close to guessing that the small, lunch-size portion of risotto, for example. contained nearly 1,300 calories. These professional nutritionists underestimated the calories in those meals by about 30 percent. Errors of that size are typical.
In another such experiment, Lisa Young asked dietitians attending an annual meeting of the American Dietetic Association to estimate the number of calories in samples of several fast-food meals. The dietitians accurately guessed the calories in a glass of whole milk but underestimated those in the mixed meals by the usual 30 percent or so. For example, when shown a typical chain-restaurant hamburger and onion rings, they guessed 865 calories on average, whereas the meal actually contained 1,550.
Calorie estimations are especially inaccurate when the food portions are large and when the foods appear to be healthy, as researchers have repeatedly demonstrated.
The Portion Size Effect
Even students trained to know that portion size influences calorie estimations get fooled by large portions. Cornell professor Brian Wansink demonstrated this phenomenon in his famous Super Bowl experiment. He invited students to his home to watch a Super Bowl game. He put half of them in one room with 2-quart bowls of snacks and the other half in another room with 4-quart bowls. The students who were served snacks from the larger bowls consumed about 50 percent more calories than those served from the smaller bowls. Both groups underestimated the calories they had eaten, but those served the larger portions underestimated by a much larger proportion.
These students should have known better. Even though they had heard lectures from Professor Wansink about the influence of large portions on the amount of food people consume, they ate more from the larger bowls anyway. And so does almost everyone else when confronted with large food portions.
The "Health Halo" Effect
People tend to underestimate the calories in foods that they perceive as healthy. This has led researchers to suggest that health claims cause a systematic bias in calorie perception. Brian Wansink and his colleagues call this the health halo effect. We think of all such marketing methods as calorie distracters. Whatever you want to call the phenomenon, much evidence indicates that marketing a product as healthy makes people think it has fewer calories:
• When fast-food restaurants position themselves as healthy, customers tend to underestimate the calories in main dishes and choose higher-calorie side dishes, drinks, or desserts.
• When portions are labeled small, people believe they are eating fewer calories regardless of the number of calories the foods contain or their actual size.
• When Oreo cookies are labeled as organic, people perceive them as having fewer calories than conventional Oreos. This happens even when the study subjects have been shown package labels indicating that calories are equal in both kinds of cookies.
Studies suggest that any health label on a food product-"no trans fat," "vitamins added," "contains antioxidants," "contains probiotics"-will encourage customers to believe that the calories don't count, or don't count nearly as much.
The Dieting Effect
Some research has suggested that overweight people tend to underestimate the number of calories they eat to a greater extent than do people of normal weight. It also suggests that the degree of underreporting increases with increasing overweight. But as Brian Wansink and his colleagues point out, underreporting is more likely to be due to the effect of the size of the meal than to weight itself. People who are overweight eat larger meals and, therefore, underestimate calories by a larger fraction. Although some studies suggest that people who are dieting deliberately underreport calorie intake, most research finds that nearly everyone underestimates calorie intake regardless of their body weights or dieting status.
The "Negative Calorie" (or Wishful Thinking) Effect
We have argued throughout this book that calories do count, so we are especially amused by the claims of some diet books that certain foods use up more calories in digestion, absorption, and metabolism than they contained in the first place-that their thermic effects are greater than their calorie values. This, of course, is physiologically impossible. The maximum thermic effect of food, as we discussed in previous chapters, is 20 to 30 percent (for protein), which still leaves plenty of calories left over. The only example of negative calories that we can think of is what happens when you drink ice-cold water. Water has no calories, but it takes some heat-about 100 calories per quart-to warm it to body temperature. A quart is quite a lot of water, and ice-cold water is not always comfortable to drink. We do not view this method as a convenient way to waste calories.
But we enjoy negative-calorie studies, and here is a favorite. The investigator came up with the idea that "people intuitively believe that eating healthy foods in addition to unhealthy ones can decrease a meal's calorie count." To test this idea, he showed bowls of chili with and without a side salad to volunteers. On average, the study subjects guessed that the chili alone contained about 700 calories. But when they saw the chili along with a green salad, they thought the meal provided only 655 calories, 45 fewer than the chili alone-as if, as the investigator put it, the salad had negative calories. People who said they were dieting were twice as likely as nondieters to make this error.
And then there are the claims of the Negative Calorie Diet, ostensibly "based on more than 100 negative calorie foods requiring your body to BURN more calories than the actual calorie content of the food itself!" On this diet you are supposed to be able to eat all you want of more than a hundred negative-calorie foods, lose weight, and not feel hungry. What are these magic foods? Just the low-calorie, high-nutrient-density fruits and vegetables that you might expect to be recommended to someone who is dieting: celery, grapefruit, lemon, lime, apple, lettuce, broccoli, cabbage, and other such items.
In practice, the negative-calorie idea sounds much like the well-researched volumetric approach developed by Professor Barbara Rolls at Pennsylvania State University. Eating low-calorie fruits and vegetables helps with weight loss because they fill the stomach and make you feel satisfied. As Julie Upton explains in an article on myths about metabolism, "A medium-size rib of celery has only about 6 calories; its [thermic effect] is approximately half a calorie. In reality, 'negative calorie foods' are nothing more than wishful thinking."
The "Calorie Oblivion" Effect
Overall, surveys and research studies consistently report widespread public misunderstanding of calories not only in food but also in the body. In May 2011, for example, the International Food Information Council, an educational arm of the food industry, published the results of its sixth annual survey of consumer attitudes toward food safety, nutrition, and health. The survey asked about perceptions of caloric intake and expenditure. Here are some of its findings:
• Only 9 percent of respondents came close to estimating the correct number of calories they might need each day.
• One-quarter thought they required 1,000 calories a day or less.
• Sixty percent said they had no idea how many calories they needed to eat.
These results were similar to those obtained a year earlier, when USA Today quoted the nutritionist Dawn Jackson Blatner: "Nobody knows how many calories they should be eating, nobody knows how many they are eating, and nobody knows how many calories are in foods. ... I would say it's beyond calorie-confused. It's calorie-oblivious."
Given widespread calorie oblivion, and short of doubly labeled water experiments, how are you supposed to know whether your calories are in balance? We know only one way: weigh yourself on a scale at regular intervals. If your calorie intake pretty much equals your expenditure, your weight should stay about the same over time, within a range of a couple of pounds. And your belt should not require adjustment.
But it is worth knowing about calorie oblivion for one other reason. The inability to judge calories with reasonable accuracy is reason enough to support better public education about calories in food and the number required to maintain body weight. And that brings us to recent efforts to improve calorie information on food labels and restaurant menus.