Category Archives: public health

Why Posting Calorie Counts Will Fail, Part I: The Number Posted is Often Wrong

Introduction to this series here.

image stolen from some article about the new policy that I lost track of because I had 70 tabs open  When you see 450 posted, that might really mean 530. Or more.

Publishing caloric values right on the menu seems straightforward and transparent. The numbers offer what appears to be a simple way to compare items no matter how different they are based on what many people believe is, as Margo Wootan said, the “most critical piece of nutrition information.”  But even setting aside for a moment the issue of whether the number of calories should be the most important factor governing food choices or all calories are equal, there are problems with the numbers themselves.

Give or take 20%…but almost always give

According to a recent study at Tufts where a team of nutrition scientists led by Susan Roberts used a calorimeter to measure the actual caloric value of 39 prepared meals purchased at supermarkets and restaurant chains:

Measured energy values of 29 quick-serve and sit-down restaurant foods averaged 18% more than stated values, and measured energy values of 10 frozen meals purchased from supermarkets averaged 8% more than originally stated. Some individual restaurant items contained up to 200% of stated values and, in addition, free side dishes increased provided energy to an average of 245% of stated values for the entrees they accompanied. (Journal of the American Dietetic Association; full-text is subscription only—here if you have UM library permission)

As Roberts told Time, she decided to do the study because when she was trying to follow the diet advice in her own book, substituting prepared or restaurant meals, “the pounds stopped dropping off. Just as suspiciously, she always felt full” (more on the idea the fullness means a diet must be failing when I get to the issue of why calorie-restriction doesn’t work for long-term weight loss).

It’s worth noting that the results of the study didn’t reach statistical significance “due to considerable variability in the degree of underreporting.” However, they “substantially exceeded laboratory measurement error” and—as noted above—the average discrepancy was 8% or 18% higher, it didn’t even out. However, the average is actually within the Federal regulations—from the same Time article:

Federal regulations are strict about the accuracy of the net weight of a package of prepared food, which must be at least 99% of the advertised weight. When it comes to calories, the count can be a far bigger 20% off. The Federal Government plays no role in checking the calorie claims in restaurants, which means it’s up to the states to handle the job — with the predictable patchwork results.

What Roberts’ research suggests is that calorie counts aren’t just wrong, they’re wrong in one direction. As anyone who’s ever tried to count calories knows, a difference of +18% could be devastating to a diet. Say, for example, you think you burn 2000 calories/day, like the supposed average American adult, and you’re trying to generate a ~250 calorie/day deficit through your diet. Assuming you continue to burn 2000 calories/day, that diet should make you lose about 1/2 lb per week or 26 lbs in a year. However, if you were actually eating 18% more calories than the 1750 you’ve budgeted, or 2065 calories/day, and the caloric algebra worked perfectly, you’d gain 6.8 lbs in a year instead.

Even if you’re being reductive, food is more than the sum of its parts

One factor that may work in the opposite direction: the method used to determine the caloric  content of food may systematically overestimate how much energy most people get from some foods. A quick primer on the calorie (most people who are reading this probably already know this, but since lots of people don’t): a nutritional calorie is a measure of the energy contained in food. The base unit, a gram calorie, is the amount of energy required to heat 1 gram of water 1 degree Celsius. A nutritional calorie is a kilocalorie (kcal) or “large calorie” (C), the amount of energy required to heat a 1 kg water 1 degree.

William Olin Atwater c. 1900 from the USDA via the Wikimedia CommonsHere’s the part a lot of people don’t know: the caloric value on labels is calculated according to the “Atwater system” named after the USDA chemist William Atwater, who spent his career burning food and excrement (cue Bevis & Buthead laughter). Based on the formula Metabolizable Energy = Gross Energy in Food – Energy Lost in Secretions, Atwater came up with average energy values for each macronutrient: 9 Kcal/g for fat, 4 Kcal/g for protein, 4 Kcal/g for carbohydrates, and 7 Kcal/g for alcohol. For the purposes of nutrition labeling, even though fiber is technically a carbohydrate, it’s subtracted from the total carb weight before the calories are calculated since it’s not digested.

However, there appears to be considerable variation within macronutrients. Sucrose burns at a lower temperature than starch and isolated amino acids vary in their heat of combustion. Additionally, the Atwater system doesn’t account for differences in how macronutrients behave in when combined—for example, fiber seems to change the amount of fat and nitrogen that turn up in feces, which suggests that its effect on caloric value might not be entirely accounted for by simply subtracting fiber grams from the total carbohydrates. And, as you might expect, “variations in individuals are seen in all human studies” (Wikipedia).

The differences between estimated calories and the actual caloric value (as measured by a bomb calorimeter like the one Roberts’ team used in their study, which still might not correspond exactly to how food is turned to energy in the human digestive tract–I’m not entirely sure how calorimeters account for fiber given that fiber is combustible even though it isn’t digestible) might not be very large—but perhaps more importantly, the discrepancies probably aren’t consistent. The Atwater system is probably more accurate for some foods than others, and seems especially likely to overestimate the energy value of high-fiber foods and distort the differences between starchy and sugary foods.

That might help to explain the discrepancy seen in studies on nuts: in controlled nut-feeding trials, people eating more calories in the form of nuts don’t gain the weight that they should based on their greater energy intake. Additionally, they excrete more fat in their feces (Sabate 2003, American Journal of Clinical Nutrition). This is similar to another issue I mentioned in the introduction—not all calories are the same—but it’s not actually the same problem. Non-random variance in the reliability of caloric estimation means that even if all calories were the same, the numbers on the menus might not be accurate, i.e. the way we estimate calories might not correspond reliably to the amount of energy people actually derive from the food they eat.

So what?

Well, this means that there are (at least) two possible ways that providing consumers with “more information” in the form of calorie counts might actually lead to worse decision-making:

1) Even if people do base their decisions about what to order on the posted calorie counts, they might end up getting many more calories than they want and eating more than think they are.

2) Certain kinds of foods—including high-fiber foods and nuts, which might be “healthier” than items with lower posted calorie counts according to more holistic metrics—might have misleadingly high calorie counts based on the Atwater system. That could dissuade customers from ordering them or restaurants from offering them in favor of less “healthy” foods that may  have lower counts based on the Atwater system but actually provide more energy.

NOTE: Comments disabled due to spam. Feel free to e-mail me with responses.

Why Posting Calorie Counts Will Fail: Introduction

Calories on menus are already a fact of life in New York City and were set to appear in a handful of states like California and Oregon in 2011. Instead, thanks to a provision in the health care legislation Obama signed in March, they’ll be required nationwide. The policy calls for all restaurant chains with 20 or more locations to publish calorie counts for all items on all menus. The policy also applies to vending machines, buffets, and bars. McDonalds menu with calorie counts from the website for the film Fat Head, click for info. I'm surprised to see that the fries actually aren't the best Kcal/$ bargain--the burgers and even the McChicken give you slightly more bang--or burn--for your buck. The profit margin on fries must be astounding.

The policy’s advocates and authors claim that it will reduce obesity rates and improve public health. In a press release from The Center for Science in the Public Interest, Margo Wootan, a nutritionist who helped write the calorie count part of the bill said:

"Congress is giving Americans easy access to the most critical piece of nutrition information they need when eating out…. It’s just one of dozens of things we will need to do to reduce rates of obesity and diet-related disease in this country…. Menu labeling at restaurants will help make First Lady Michelle Obama’s mission to reduce childhood obesity just a little bit easier.” (CSPI press release)

In an interview with the LA Times, she expanded on the logic of the claim: 

"People will be able to see that the order of chili cheese fries they are considering will be 3,000 calories.”

Well, probably more like 400500. But how could she be expected to know that before the law goes into effect?

Kelly Brownell, director of the Rudd Center for Food Policy and Obesity at Yale told the NYTimes that even if some consumers ignore the information, it will affect enough people to create a public health benefit. However, he also hedged his bet—saying that even if it doesn’t make people eat better, it’s an issue of rights as much as an issue of health:

“You don’t need a study that proves anything,” Mr. Brownell said. “You just have a right to know.”

Proof? Who needs proof? His disclaimer is savvy, because now in 5 or 10 years if obesity rates are still the same* or higher and there’s been no significant decrease in cardiovascular disease, diabetes, cancer, or any of the other conditions correlated (albeit often weakly) with obesity, Brownell can claim we’re still better off knowing than not knowing.

I’m not so sure. While I don’t think posting the number of calories is likely to have a significant, negative impact on public health, nutrition is one realm where more information isn’t always better. The usefulness of information always depends on its reliability, relevance, and people’s ability to place it in meaningful context. Calorie counts fail on all three measures, which is why I suspect the new policy isn’t going to have the desired effect on obesity rates or public health.**

Here are a few of the problems with calorie counts I’ll address in this series:

1) The number posted is often wrong (a problem for reliability)

2) Most people don’t know how many calories they burn (a problem for meaningful context)

3) Even though calorie restriction is a highly effective short-term weight loss strategy, it doesn’t work long-term (at least for 90% of dieters) (a problem for relevance)

4) Not all calories are equal (another problem for relevance)

Furthermore, the limited evidence available so far about how calorie counts on menus affect purchasing decisions based on the New York City law is mixed. That calls into question the mechanism by which the policy is supposed to improve public health. Apparently, knowing the calorie content of menu items doesn’t necessarily reduce the number of calories people purchase. And that’s before even beginning to try to measure whether purchasing fewer calories on single visits to restaurants actually leads to weight loss or if people just compensate by eating more on other occasions or eating more often.

One response might be: well, it can’t hurt. I’m also not so sure about that. While I don’t think it’s likely to make public health worse, by reinforcing the idea that your health (or your weight) is based on the number of calories you eat, it may prevent people from taking steps that would actually improve their health, which the preponderance of evidence suggests that calorie-restriction dieting will not.

Part I in this series, on why the number posted is often wrong, coming later today.

*The rate of increase in obesity has already been slowing down so even if it plateaus, that’s not necessarily evidence this or anything else is “working,” it may simply mean that obesity rates have reached an upper limit.

**Two separate issues which are often unjustly conflated. For more on that, see Paul Campos’ The Obesity Myth, J. Eric Oliver’s Fat Politics, Glen Gaesser’s Big Fat Lies, or Michael Gard and Jan Wright’s The Obesity Epidemic: Science, Morality, and Ideology—if you feel like I’ve said that before, it’s because I have. The reason I bring them up again and again is that they completely changed my thinking about nutrition, fatness, and health. The authors of those books all—independently—examined the evidence for the argument that obesity is dangerous and all reached the same conclusion: it’s not, and the belief that it is is based on some shockingly bad science. They also argue convincingly that the actual increases in Americans’ weight in the last few decades are actually quite modest (it’s the rate of people being defined as obese that’s trumpeted, not the amount of weight people have gained on average and some of the increase is based on changes in the definition of “normal” or “healthy” with no medical justification); that the correlations between obesity and disease or early mortality—many of which are quite weak—can be entirely explained by other factors that also happen to be correlated with BMI like differences in physical activity, income, and insurance status; and that weight-loss dieting, especially low-fat and calorie-restrictive dieting, do more harm than good. You don’t have to take my word for it. Substantial portions of the books are available for free online, as are many of the studies they cite (including the CDC study that revised the widely-cited statistic that overweight and obesity causes 300,000 deaths per year in the U.S. and said, effectively, “Actually make that 26,000 and by causes we mean correlates with.”)

NOTE: Comments disabled because of spam, but I welcome e-mail responses.