How eating several smaller sized chocolates makes you look greedy and impulsive: the unit size effect of indulgent food

Imagine you are offered a package full of delicious chocolates. Would the size of the pieces of chocolate influences how much you eat?

Yes, the size of your piece of chocolate matters. This so-called unit size of food refers to the number of units in which a portion of food is divided. Earlier studies have shown that smaller units typically lead people to eat less. For example, Wansink and colleagues found that people being given four 100-calorie packs of crackers ate about 25% less than when given one 400-calorie pack. But why does this happen? Is it because everytime you start with a new piece, you realise you are still eating and wonder whether that is a good thing? A kind of pause moment? Or do other psychological processes play a role?

In a series of studies together with Hans van Trijp and Christos Kavvouris (published in Psychology and Health), we show that with a small unit size, people eat less because they have the impression (that others think) they eat more and are impulsive. Feeling or looking impulsive is something that many people want to prevent in our society.

Judging someone else eating chocolate (experiment 1)

In our first experiment, participants watched a movie featuring Michelle enjoying chocolate during a break. Half of the participants saw Michelle eating five small chocolates (about 50 grams in total). The other half of the participants saw Michelle eating exactly the same amount of chocolate, but now she ate one big chocolate bar. Interestingly, even though she ate the same amount of chocolate, participants considered the amount to be more excessive, impulsive and inappropriate in the case of the smaller pieces. 

 

Michelle eating 50 grams of chocolate in 5 small pieces (left) or 1 large piece (right)

 

Eating a fixed amount of chocolate (experiment 2)

In a second experiment, we asked one group of participants to eat all 5 small chocolates (50 grams) and another group to eat one entire large chocolate bar (50 grams). We asked them to imagine that they choose themselves to eat the amount they ate. Again, despite consuming the same amount of chocolate, eating smaller sized chocolates felt more excessive and inappropriate than eating one large piece.
 

Eating as much as you like (experiment 3)

Now participants got either 15 small-sized chocolates (150 grams) or 5 large-sized chocolates (also 150 grams) in a supposed taste test in which they were free to decide how much to eat. We also varied the wrapping of the chocolates (see picture below). Unwrapping a chocolate may draw attention to the decision to continue eating, which makes it less automatic.

About 23% less chocolate was eaten when it is presented in smaller units. Participants ate most in the groups being presented with unwrapped large chocolates. This unit size effect could be explained by people feeling more impulsive eating several smaller sizes chocolates than eating a large size chocolate.



Equal amounts of chocolate in the 4 conditions of study 3

Enjoy more, eat less
Across studies, the unit in which the chocolate was offered changed people's perceptions. Eating smaller units looks and feels more excessive and impulsive. Feeling more or less full had nothing to do with it. This brings us back to research on the numerosity effect in the 1990s. Essentially, we think that more pieces of something usually turn out to be more of something. In other words, bigger numbers equal bigger quantities. For example, a seven seater care is usually larger than a five seater car. A quick decision strategy that leads to good decisions most of the time, but it may also lead to wrong estimations.

Clearly, unit size is a cue that helps people to assess what an acceptable portion is. Smaller sized portions may help consumers to control themselves and eat less. Food companies could make item sizes smaller (indulgent snacks such as ice cream scoops or candies) or bigger (fruit, vegetables, whole wheat bread slices), depending on whether you want to make consumers effortlessly eat less or more.

van Kleef E., Kavvouris C. & van Trijp H.C.M. (2014). The unit size effect of indulgent food: How eating smaller-sized items signals impulsivity and makes consumers eat less, Psychology & Health, 1-41. DOI: 10.1080/08870446.2014.909426

Controversial marketing: The hidden empty calories in soft drink vendings machines at high schools

Last month, I visited a high school Open House with my almost 12 year old daughter. One of the staff members proudly told parents that the canteen only serves healthy foods. Good news. However, to my surprise I bumped into a soft drink vending machine in the hall way selling various sugary drinks (see picture).

Last week, a documentary about the powerful sugar and soft drinks lobby in the Netherlands opened my eyes (Zembla: De Zoete Verleiding). At 37 minutes into the documentary, a Dutch school principal states that the school earns about €19.000 each year thanks to a so-called 'pouring contract'. The school gives exclusive permission to sell soft drinks in vending machines in hallway or canteen ('pouring rights'). Although most revenues go to the soft drink company, for schools these contracts are very lucrative. It is a substantial source of revenue to pay for all kinds of extra school activities such as music and sports.

Since the 1990s, targeting schools has been an important strategic direction of soft drink companies. School children are a highly relevant group to continuously confront with brand logos and advertising. It is a great opportunity to create a new generation of loyal consumers. However, it is a questionable marketing practice. Perhaps schools underestimate the negative consequences of consuming soft drinks at a regular basis. If that is the case, they should wake up. A recent study among 641 Dutch school children showed that children given sugar-free drinks gained less weight than those given regular drinks with sugars. This study adds to the growing evidence that sugary soft drinks directly contribute to obesity among children. As such, soft drinks are the prototype of junk food.

Reversing the obesity problem requires immediate action. I am in favour of using psychological insights to nudge consumers towards healthier food choices. Subtly pushing children towards healthier choices, for example by making fruits and salad more accessible, is a promising way to go. Increasingly, vending machines include healthier options, such as water. However, as a consumer scientist and a mother, I wonder whether a nudge is strong enough. Soft drinks are a huge temptation compared to water. Water is less cool and tasty. Seeing 'everyone drinking it' may influence my daughter to leave her common sense behind. Moreover, that athlete at the display looks real good. As teenagers are in the process of learning to control themselves, they need strong support at home, but also at school. Add this to the substantial financial benefits for both the soft drink industry and schools and I believe that we strongly need to consider banning soft drinks in school vending machines.

Why 'black and white' thinking makes you eat more

Many dieters who lose a lot of body weight will be back where they started or even heavier. Some dieters, however, manage to keep off some or all the weight. In a study of Susan Byrne and colleagues, aimed to learn more about successful and failing dieters, the most powerful psychological predictor of weight regain was a dichotomous thinking style. This thinking style is also called 'black and white' or 'all or nothing' thinking. Dieters think they have to eat perfectly or do nothing at all.

Dose insensitivity

Not only dieters, but many consumers label foods as either 'good for health' or 'bad for health', without any options in between and regardless of the amount eaten. In a survey of Paul Rozin and colleagues, 40% of the respondents agreed with the statement 'Although there are some exceptions, most foods are either good or bad for health'. They call this tendency to believe that something in large amounts is also harmful in small amounts 'dose insensitivity'.

People overgeneralize even to the level of gaining weight from eating foods. In a study of Michael Oakes and Carole Slotterback, participants were presented with food and their caloric content. One of their fascinating findings? One bag of potato chips (152 calories) was judged to promote more weight gain than a large raisin bran muffin (460 calories).

Venco Zwart-witjes Liquorice - good or bad?

The advantage of this thinking style is that it makes life simple and reduces the number of choices you have to make. You chose a 'good food' and you can eat how much you want, without worrying about gaining weight. Perhaps this tendency is not surprising as consumers are bombarded with advertising and claims focusing on benefits of consuming one food or meal. Perhaps even some over simplistic nutrition education campaigns can partly be blamed ('beware of fat').

This 'black and white' mind-set can make you overeat. No matter how large the portion size, you are likely to underestimate your calories and as a result overindulge. Dieters thinking 'black and white' also talk negative to themselves. Once they break a diet rule, pessimistic thoughts come up, such as: 'Now I have blown it; I ate three chocolates, I might as well finish the entire box' or 'this is not a dieting day anymore...'.  Consequently, they do not stop eating and ignore physical feelings of fullness ('what the hell effect').

Do you agree with the statement: 'I don't want to give up the foods I like'?

I do, and I am not alone in this. In a survey of the Academy of Nutrition and Dietetics, 82% of the respondents agreed with this statement. It is hard to abandon foods from your life that you really love. Tell yourself 'you can't eat that!', and the more tempting it becomes. It may help to identify such thinking patterns and replace them with a more realistic view on eating. For example, enjoy a little snack, just don't go overboard.

Impulsive snacking at the checkout counter: nudging consumers towards healthier 'grab-and-go'-snacks

Candy aisle near checkout 

Tempting snacks placed right near the checkout counter can be hard to resist. Even though you know buying one is not in your best interest, they catch attention. These high-profit 'grap-and-go' snacks are particularly hard to ignore at the end of a shopping trip after making dozens of decisions. Even at my local shoe store, they tried to tempt me in buying candy (see picture).

In our recent paper published in BMC Public Health, we (that is Hans van Trijp, Kai Otten and myself) report two nudging studies on whether assortment structure and accessibility of healthier snacks influences consumer choices. The idea was that providing a larger assortment of healthier snacks and putting them on top of shelves makes these snacks more salient, attractive and convenient, leading hopefully to higher sales.

To test this idea, we first carried out a study among students in which we asked them to make a hypothetical choice from a shelf displayed at their computer screen. The results of this study showed that when the majority of snacks is healthy, students were are more likely to choose such a snack. Although this may seem obvious, they were equally satisfied with their choice and did not feel restricted.

However, lab studies do not always provide reliable predictions about how people behave in real-life. Therefore, we conducted a  field experiment in hospital 'De Gelderse Vallei'. We now put an actual snack shelf near the checkout of the staff canteen. Each week, an alternative snack assortment was on display. The assortment included either 25% or 75% healthy snacks. We also altered their place on the shelf (either on the higher shelves or the lower shelves). On completion of the study, we also conducted a brief survey among employees.

When 75% of the assortment consisted of healthy snacks, sales of healthy snacks were higher. In contrast to our expectations, putting healthy snacks at the most convenient (top) shelf space did not impact consumer choices and sales. It could be that our manipulation was not strong enough (see picture). Interestingly, the majority of surveyed employees did not notice assortment changes. When asked, however, they preferred the shelf displays including the larger variety of healthy snacks.

Overall, these studies show the size of a healthy assortment of snacks matters. A relative large assortment of healthy snacks is able to influence consumer choices. However, we do not know whether this intervention really leads to better snacking habits at the longer term. Moreover, these types of interventions are typically more successful in canteens than those in restaurants and grocery stores, where financial interests are at stake.  


While not all nudges are effective (see for example our nudging study among children), this nudge might be worth to give a try. Without forbidding any foods, a larger assortment of healthy snacks may catch consumer attention and even seduce them to purchase. 


Nudging paper in BMC Public Health: Healthy snacking at the checkout counter: a lab and field study 


van Kleef E, Otten K, & van Trijp HC (2012). Healthy snacks at the checkout counter: A lab and field study on the impact of shelf arrangement and assortment structure on consumer choices. BMC public health, 12 (1) PMID: 23231863

Recommendable book to boost your willpower: The Willpower Instinct of Kelly McGonigal

The best way to make sure you never again give in to temptation (such as eating another chocolate) is to beat yourself up, so that you will never do it again. Quite logical, isn't it? However, it turns out that this is not such a clever way to motivate yourself, because if you feel guilty, this negative feeling is most likely to disappear by eating more. As a result, cheating a little may lead to the infamous 'what the hell effect'.


This is one of the many self-control undermining processes discussed in the book 'The Willpower Instinct' of Kelly McGonigal. Recently, it has been translated into Dutch ('De kracht van wilskracht - Hoe zelfbeheersing werkt en wat je eraan kan doen').

Willpower is one of the hottest topics in research and studied in a diverse range of fields. This book clearly explains the science behind willpower, how it functions and what key problems are. Moreover, informed by numerous studies, the author offers useful strategies to deal with tempation in daily life. After reading this book, it is obvious that willpower is much more than a simple 'just do it' strength that you need to finish your 'to do'-list or drop a few pounds of overweight.

What I particularly like are the chapters about the role of dopamine in anticipation of rewards. When you expect, see or eat food, the brain releases dopamine and gets excited. You can override this automatic system by using your prefrontal cortex in the front of your brain, which is responsibe for more reflective and conscious decisions. Indeed, that is where willpower is located in your head. Unfortunately, this cortex has many things to worry about and gets easily distracted. Small changes or new habits that make you remind your goals and create awarenes such as meditating and exercising will build the foundation for more enduring change. They make your willpower system more efficient and fuelled to do its tasks.

This book is definitely a must-read, also because willpower is not presented as a miracle solution to life's challenges. Yes, you can get more of it, but it has its limits. That reminds me of a sentence I read in a paper of Hofmann, Friese and Wiers (2008): 'Human life would be less pleasurable without our propensity to act impulsively: An over-controlled life can be even psychologically and physically damaging.' So, train your willpower, but give yourself the occasional break.

3 surprising insights on how food cravings relate to other desires in everyday life

What is harder to resist? Checking your Twitter or Facebook account at work or eating a delicious, but fattening snack when you try to watch your calories? Both are inner conflicts, best described as 'I really want to do this, but I should not'.

In many food studies it is assumed that people have conflicting feelings when being confronted with tempting foods. But is that really the case in everyday life? What type of cravings are felt most strongly? And if people do crave foods, how often are they trying to resist their desire?

Wilhelm Hofmann, Kathlees Vohs and Roy Baummeister recently tried to answer these questions in their Everyday Temptation Study. They gave BlackBerrys to 205 participants and contacted them on 7 random times per day for one week. When they were contacted, they had to indicate what type of desire they experienced within the last 30 minutes, how conflicted they felt about this desire, whether they tried to resist the desire and how successful they were in this. The study included all types of everyday desires, including the desire to eat, drink, have sex, sleep, spend money and use media (such as social media). Here are 3 insights that I found most surprising.

1)   Food is not the hardest desire to resist
People feel some desire about half the time they are awake. In hours, this is about eight hours a day. Almost half of those desires are conflicting at least somewhat with other goals in life.
Interestingly, food is not the hardest desire to resist. It is much more difficult to fight the desire for sleep and fun leisure activitities (such as checking Facebook). These two were considered to be the hardest to resist. Only 23% of all conflicting desires go against some health goals (for example healthy eating or exercise). The majority of reported inner conflicts were related to goals such as saving money, achievements at work or study, social appearance and efficient time use.

In other words, it is harder to resist impulses to spend money, participate in sports, use (social) media and smoke than it is to resist eating.

2)   We spend three hours a day resisting desires
The majority of desires in everyday life are not resisted. We have to eat anyway, so why trying to resist it? When people do try to resist them, they are quite successful in it; in 83% of all inner conflicts, they succeed to not give in. Still, in 17% of all occasions, people do give in. They particularly fail to resist checking e-mail, Facebook, Twitter of other social media when they do not want to do that.

3)   Stop resisting the numerous cravings throughout a day
Besides that we spend about three hours per day resisting desires, we also spend half an hour giving in to desires that we initially resisted. The more often you try to resist a desire, the less willpower is left at the end of the day and the more likely it is that you go for the 'forbidden' food. This confirms the 'muscle model' of willpower, which states that willpower is like a muscle that needs refuel.

So, do not replete your willpower, stop reading this blog post and go back to work.



What is harder to resist; Twitter and Facebook at work or the temptation of an unhealthy snack?

Hofmann W, Baumeister RF, Förster G, & Vohs KD (2012). Everyday temptations: an experience sampling study of desire, conflict, and self-control. Journal of personality and social psychology, 102 (6), 1318-35 PMID: 22149456

Wanting to eat healthier, but little healthy foods sold at McDonalds

Most fast food restaurants do not share their sales data of healthy foods, but that did not stop Lyndall Wellard and colleagues to find out how many healthy items are actually sold at the biggest fast food chain in the world. They observed what people bought at 20 McDonalds restaurants in Australia. Of the 1449 meal purchases observed, only 1% could be considered healthy, 65% were unhealthy and 34% were take-away (so impossible to determine whether food is healthy or not).

Only 1% of all meals eaten in the restaurant! That is not much... Why would you sell healthy foods in a restaurant when hardly anyone is buying it? As a service to the 1% die-hard dieters who really do not want burgers and fries? Or to create a healthier image which may lead to higher overall sales?

According to a survey among Americans, 47% said they wanted restaurants to offer healthier items like salads. Even 23% said they tend to order those foods. Apparently many consumers like to have these items on the menu. Maybe as a license to indulge? Research of Wilcox and colleagues already showed that adding a salad or fruit to the menu makes you more likely to order fries. And to make it worse: consumers also tend to believe that adding a healthy item to a meal magically decreases the number of calories of the total meal.

In my previous blog post, I discussed the essay of Marion Nestle and David Stuckler on the influence of large food companies on public health. They are right, healthier foods are inherently less profitable. At least when eating out, most consumers seem to just want to indulge (without feeling too guilty).

The Oprah Paradox: why people with excellent self-discipline also have a hard time controlling their body weight

Willpower has typically been looked at as a trait that one has or has not. For decades, self-esteem was the concept that needed to be promoted while self-control was viewed as old-fashioned. But willpower is back in fashion as research has shown that it is a key positive factor predicting happiness and well-being.

I just finished reading the book 'Willpower' of Roy Baumeister and John Tierney (In Dutch: Wilskracht: De herontdekking van de grootste kracht van de mens). Roy Baumeister is a leading scientist in the field of willpower and self regulation and became widely known for the process of 'ego depletion'. Having too many choices will exhausten your self-control as we draw on the same source of willpower for various tasks, not just related tasks. That means that willpower is like a muscle which needs to be fuelled by sleep and food (glucose).

Wilskracht - Baumeister & Tierney

In chapter 10, Baumeister and Tierney discuss what they label the 'Oprah Paradox'. Oprah Winfrey must have had excellent self-discipline and willpower to achieve the success that she did. Nevertheless, even she has a hard time to consistently control her weight. The authors discuss this paradox by listing some reasons why dieters fail. In order not to eat, a dieter needs willpower. Willpower runs on glucose. So, to fuel willpower, a dieter needs to eat. In other words, dieters deprive themselves from what they need the most. Another big threat is that dieters often fall for the so-called 'what the hell effect'. A small slip in their diet will make them blow off the dieting rules entirely. Dieting is obviously not the solution. The authors argue for small manageble changes. Over time, these small changes will become habits and having good habits saves willpower.

Overall, this is a book absolutely worth reading as it clearly shows how important willpower is. In an entertaining way the authors offer advice on how to strengthen self-control and use willpower wisely. One of them is: never say never when it comes to dealing with tempting foods. It is better to tell yourself to eat a small portion later than forbid yourself to eat them at all. This postponement method allows the impulse to fade away and in this way encourages self-control.