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The Dieters Paradox – Research Review

Chernev A.  The Dieters Paradox.  Journal of Consumer Psychology.  (2001) 21: 178-183.

Despite the vast public policy efforts to promote the consumption of healthy foods and the public’s growing concern with weight management, the proportion of overweight individuals continues to increase. An important factor contributing to this obesity trend is the misguided belief about the relationship between a meal’s healthiness and its impact on weight gain, whereby people erroneously believe that eating healthy foods in addition to unhealthy ones can decrease a meal’s calorie count. This research documents this misperception, showing that it is stronger among individuals most concerned with managing their weight—a striking result given that these individuals are more motivated to monitor their calorie intake. This finding has important public policy implications, suggesting that in addition to encouraging the adoption of a healthier lifestyle among overweight individuals, promoting the consumption of healthy foods might end up facilitating calorie overconsumption, leading to weight gain rather than weight loss.



In introducing today’s paper, I am reminded of an old joke/quip to the effect that “All that separates man from the animals is our ability to rationalize.”   I’d add “And accessorize” but that’s neither here nor there.  But the reality is that humans are able to do a wide variety of mental gymnastics in how they approach life.  Effectively, we appear to be slave to what psychologists call cognitive biases, ways in which we think about the present, past, future or ourselves that often lead us to make some fascinatingly bad choices.  This is a topic that many recent books has discussed in a variety of contexts.

And while I don’t know if I can say that it occurs to a greater degree in terms of eating and health behaviors, there is no doubt that people often engage in some exceedingly interesting mental gymnastics when it comes to those topics.  Some of this is conscious but much of it can be chalked up to either unconscious behaviors, misunderstandings (or a lack of information/education) or mishearing/misinterpreting the message.   And these types of things, as much as anything else, often derail many people’s attempts to eat healthy, lose weight or simply avoid weight gain.

In the realm of exercise for example, many people grossly overestimate the actual caloric expenditure from activity, as I discussed in Normal Weight Men and Women Overestimate Energy Expenditure – Research Review, and this leads them to either expect far more of an impact on weight loss than is realistic or to eat more calories than they actually need based on the assumption that they burned it off during activity.

In the arena of eating, this issue can show up in a myriad ways.  A classic example of a misunderstanding/garbling of the message occurred back in the 80’s during the low-fat eating craze.   While it’s hard to say where the blame lies, the general public sort of got the message that so long as they kept fat intake low, nothing else really mattered.  Caloric intake and portions went out the window.

Food companies capitalized on this by rushing plenty of energy dense, high-calorie (but low-fat) foods to market and it all went wrong.  Studies routinely found that people ate more food when it was labelled ‘low-fat’ compared to one that was labelled as being higher in fat.  Either consciously or unconsciously, they gave themselves permission to eat more of it.  And often ended up consuming more calories than they would have otherwise.

Another example deals with artificial sweeteners where you often see a pattern where artificial sweetener (or diet soda) intake is associated with weight gain (or a lack of weight loss).  And while there is some speculation that artificial sweeteners do some odd things in the brain in terms of driving appetite, it’s probably more related to people rationalizing that they can eat more of something else because they are getting less calories by choosing diet soda or using artificial sweeteners.   That is, they figure that since they are ‘saving so many calories’ by making one choice, they end up compensating (or more than compensating) by choosing something unhealthy.  Call this the skim milk and chocolate cake or Diet Coke and cheeseburger approach to eating.

I’d note before continuing that this much of the above rationalizing tends to be more for people who are only paying somewhat ‘superficial’ attention to ‘eating well’ (or some other fairly abstract goal).  That is, the type of thing I’m going to talk about doesn’t generally occur among folks who are diet obsessed and track macros or calories or what have you.  Rather it’s for folks who, while they may say that they are concerned with their diet or body weight or body fat, are focusing on the wrong things (a topic I addressed in more detail in Fundamental Principles vs. Minor Details).

Finally type of behavior seems to occur more prevalently in people who tend to divide foods into ‘good’ and ‘bad’ categories (a category that many popular diets and dietary approaches tend to promote).  ‘Good’ foods become equated with healthy and, altogether too often, can be eaten without consequence (i.e. weight gain).  Researchers call this the ‘health halo’ by which supposed ‘healthy foods’ have a halo of invincibility around them  In the same vein ‘bad’ foods are equated with being unhealthy and this categories are not only absolute but cause us to do some of those strange mental gymnastics when it comes to how we approach our food intake.

You can find examples of this all over the place where people assume that ‘healthy/good’ foods can be eaten in uncontrolled amounts whereas the tiniest amount of ‘unhealthy/bad foods’ mean that the diet has failed, the dieter is immoral and weak, and health will simply be destroyed (this is seen at the greatest extreme in a psychological condition called orthorexia whereby people see food as a moral choice judging not only themselves but others by the foods that they choose to eat).  You can see some good examples of this in the comments section of Straight Talk About High-Fructose Corn Syrup: What it is and What it Ain’t. – Research Review.

Which basically segues into today’s paper which examines a behavior pattern that is often seen whereby folks tend to get fixated (or perhaps ‘blinded’ is a better word) by the concept of ‘healthy’ foods and end up missing the forest for the trees when it comes to their food and caloric intake.   There is also evidence that people who are (or at least state that they are) more ‘weight conscious’ are even more prone to make these kinds of mis-estimations which was a secondary aim of the study.


The Paper

The study recruited 934 people, of whom the majority (74.2%) were female aged anywhere from under 20 to over 50.  Subjects were then shown 4 meals which either consisted of ‘unhealthy’ foods or those same unhealthy foods coupled with a healthy option.  The four meals, with the healthy addition shown in parentheses, were a hamburger (three celery sticks), bacon and cheese waffle sandwich (small organic apple), chili with beef (small salad without dressing) and meatball pepperoni cheesesteak (celery/carrot side dish).   So, for example, subjects were either shown a bacon and cheese waffle sandwich (which sounds amazing in so many ways) either by itself or side by side with a small organic apple.

Half the subjects were shown the unhealthy choice alone and the other half were shown the combination of the unhealthy choice with it’s healthy add-on and they were asked to estimate the caloric value of the meals.  I’d mention that this design is problematic because it’s not comparing how a given individual might rank each of the two meals; rather it’s comparing the average estimate of the caloric value of the different meals between people.  All subjects were also asked to rate how concerned they were with managing their weight on a scale of 1-5 (with 5 being extremely concerned).

The study generated a total of 2750 total observations of the different meals and, on average, subjects estimated that the unhealthy meal alone contained 691 calories.  Now, logically it’s obvious that a food consisting of an unhealthy item PLUS a healthy item would have to have more calories than the unhealthy item alone.   Clearly two foods can’t have less calories than either food alone.

Yet, on average, subjects estimated the unhealthy plus healthy choice as having only 648 calories.  I’d mention that as a third part of the study, a separate group was asked if they believed that the healthy foods contained negative calories and this was not the case.  So it doesn’t appear to have been the case where subjects figured that the healthy addition was literally ‘reducing’ the caloric value of the food by containing negative calories.  Rather, the ‘health halo’ effect caused people to systematically underestimate the caloric value of the combination of an unhealthy and healthy food.

But it gets even odder.  When the estimates were ranked by how folks reported their concern with managing their weight, the values changed even more.  The most ‘weight conscious’ subjects estimated the unhealthy meal as containing 711 calories while the combination of the unhealthy and healthy choice was only 615 calories. In contrast, the non-weight conscious individuals estimates were only 684 for the unhealthy choice versus 658 for the combination and there was a direct relationship between how weight conscious the subjects were and their mis-estimate of the different meals.


My Comments

I really don’t have a ton to add to the above, the paper goes into lot of discussion that I’ll spare you here since it’s a lot of detailed examination of the possible underlying mechanisms behind these types of odd cognitive biases.   One point that was made was that while one might expect more motivated/involved people to have less problems with these types of conceptual biases, this research found the opposite.  To whit:

The negative calorie bias is more pronounced for more involved/motivated individuals. Thus when evaluating vice/virtue combinations, greater motivation does not necessarily result in greater accuracy but instead can lead to more biased judgments.

I would add that I think really has more to do with what I mentioned in the background above, the issue isn’t with dietary motivation per se but rather with how people often conceptualize the process.  By focusing on things like good/bad foods, clean vs. unclean eating, meal frequency exclusively or organic vs. non, people lose sight of the issue of portions and calories which are what really matter when it comes down to it. They rely on estimates which are oh so often off.  And which appear to be colored heavily by the cognitive biases that many humans are so prone towards.

Make no mistake, certain types of eating patterns often automatically get people to reduce their intake, often by the outright removal of a so-called ‘bad’ food.  What is defined as good or bad depends on the diet in question and certainly these types of good/bad approaches to dieting can work in at least the short-term (and sometimes longer than that).  The problem is when people start focusing on the goodness/badness of the foods they are eating to the exclusion of everything else.  That’s when it often goes wrong; this is not helped by many dietary approaches telling folks that calories/portions don’t count and that focusing only on the aforementioned ‘good/healthy’ foods is all that matters.

In this vein, the paper’s author notes that:

In particular, the negative calorie illusion has been shown to be less pronounced when individuals pay attention to the quantity of the combined items, instead of focusing solely on the healthy/unhealthy aspects of the items.

In a related vein, the author points out that:

Another public issue raised by this research concerns the viability of promoting the very notion of stereotyping foods into vices and virtues.  Despite it’s intuitive appeal as a decision heuristic to simplify choice, vice/virtue categorizations focuses consumers’ attention only on one aspect of the meal [my note: whether the food is a ‘vice’ or a ‘virtue’] and ignores other important aspects such as its overall quantity.

And I really think that that’s the big take home message of this rather odd paper: people often get so fixated and focused on the wrong things that they end up hamstringing their own attempts to reach their goals.  Because while it’s all well and good to focus on healthy/unhealthy, good/bad, clean/unclean or whatever, at the end of the day quantities always count.  When people lose sight of that and focus on the wrong aspects exclusively, they often end up hurting their own progress.  This paper just points out one way that this happens.

I’ll finish by pointing interested readers to a book by the paper’s author titled  The Dieter’s Paradox: Why Dieting Makes Us Fat that addresses not only this research but a great deal of other research looking at similar issues.  How humans tend to categorize foods into good and bad and how it can lead them to make a lot of really weird assumptions about what they are actually eating.  It was a pretty fascinating read and shows how many different ways we can end up screwing our own progress by relying on our (often incorrect) intuition, primarily by focusing on the wrong factors that are relevant to what we are eating.

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