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

Portiegrootte bepaalt sterk hoeveel we eten; of het nu komkommers zijn of chips

Kinderen worden in ons land steeds zwaarder; ongeveer 1 op de 8 kinderen heeft overgewicht. Dit komt niet alleen door te weinig beweging, een belangrijke reden is ook dat we steeds grotere porties eten. De laatste decennia zijn portie groottes van veel voedingsmiddelen gegroeid. Een voorbeeld is de familiefles Coca-Cola die in 1957 werd geïntroduceerd in ons land. Deze fles bevatte maar 750 ml cola. Nu bevat een familiefles het dubbele of zelfs 2 liter. Dit fenomeen is ook te zien bij plakjes kaas, zakken chips en bakjes friet. Als consumenten houden we van ‘waar voor ons geld’ en fabrikanten en restaurants gaan hier op in door grotere porties aan te bieden. Onderzoek heeft echter laten zien dat mensen helemaal niet zo goed zijn in het bepalen van wat een normale portie is. Wat op ons bord of in de verpakking zit eten we voor 95% op. Het blijkt dat we dit teveel aan eten meestal niet compenseren door later minder te eten. Dit wordt ook wel het ‘portie grootte effect’ genoemd en is een belangrijke oorzaak van het overgewichtsprobleem.

Maar wat als we dit ‘portie grootte effect’ gebruiken om kinderen meer groente te laten eten? Groente bevat vitamines, vezels en is van nature ‘light’, maar kinderen eten er, net als veel volwassenen, te weinig van. Ga je ongemerkt meer eten als je meer krijgt, of stop je omdat je vol zit of je het niet meer lekker vindt? Deze vragen waren, kort gezegd, de aanleiding van de ‘komkommerstudie’ waarin 255 kinderen van de basisscholen de Springplank in Rhenen en de Koning Davidschool in Ede aan hebben meegedaan. Ilse Bruggers heeft de studie uitgevoerd als haar afstudeerproject, begeleid door mijzelf en Emely de Vet.

Hoewel een koekje de populairste schoolsnack bleek te zijn (bijna 77% van de kinderen gaf aan koekjes mee te nemen naar school), namen alle kinderen enthousiast deel aan de studie. ‘Ik vond het heel leuk en lekker! Kunnen jullie de volgende keer terugkomen met aardbeien?’ schreef een 9-jarige meisje op de vragenlijst. Elke klas kreeg de komkommer op een andere manier aangeboden. In sommige klassen kreeg elk kind wel twee derde komkommer en in andere klassen een derde. We varieerden ook de grootte van de stukjes; sommigen kregen plakjes komkommer en andere een heel stuk. Er mocht net zo veel of weinig gegeten worden als je wilde; zelfs niets of alles opeten was prima. Na het invullen van een vragenlijst namen we de resten op het bordje weer mee en wogen hoeveel elk kind gegeten had.

De resultaten waren duidelijk; hoe groter de portie komkommer op het bordje, des te meer er werd gegeten. De kinderen aten gemiddeld wel 54% meer komkommer. Dat is al ruim 70 á 93% van de aanbevolen dagelijkse hoeveelheid groente voor kinderen tussen de 9 en 13 jaar. Of de komkommers nu in stukjes waren gesneden of niet had geen invloed op hoeveel de kinderen aten. De grote stukken komkommer maakten wel indruk; kinderen dachten dat ze meer gegeten hadden dan de kinderen die dezelfde hoeveelheid in plakjes voorgeschoteld hadden gekregen. Wat betekent dit nu in de praktijk? Als u wilt dat u kind meer groente of fruit eet, geef dan meer. Snijd het wel even in stukjes, dan hebben ze niet door dat ze er veel van eten.
 

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.

Just a bite or the full portion size? Dramatically smaller snack portion sizes satisfy hunger and cravings

A key reason we are getting overweight is because we eat too large portion sizes of food. But is this overeating giving us more satisfaction? Could eating smaller portions be similarly effective in decreasing food cravings or feelings of hunger as larger portions? That was the key question in the study that I conducted with Mitsuru Shimizu and Brian Wansink while visiting the Food and Brand lab. The paper is now published in Food Quality and Preference (see also full-text paper).



We presented 104 participants with either a small portion of three commonly craved snacks - chocolate, potato chips and apple pie - or substantial larger portions of the same snacks. For example, the small portion of chocolate was 10 grams, while the large portion was 100 grams. Feelings of hunger and craving were assessed just before participants started with the taste test, immediately after the taste test and about 15 minutes later. Secretly, we also measured how much participants ate.

Results show that although providing larger food portions increased snack calorie intake by 77% (103 calories), after 15 minutes, they do not reduce hunger or cravings any more than smaller portions. In other words, after 15 minutes, when all food was out of sight, everyone was equally happy.

A typical snack in the US contains about 264 calories (see Piernas and Popkin, 2010). This amount closely resembles the total calories consumed in the large portion size condition in our study (about 237 calories). Nevertheless, although participants in the small portion size condition ate considerably less (about 134 calories, which is about 51% of what people typically snack), they were equally tempted by the snacks. This shows that whereas large portions tend to increase food intake, smaller portions may make you equally satisfied. 

Going for the large portion size of their favourite food

How to stop eating when you are craving a food? One way is to make sure that there is less food in front of you in the first place. That is not simple. Large food portions are common in supermarkets, restaurants and even at home. Portion sizes of many foods have increased during the last decades and we are getting used to it. For example, snack foods and beverages are offered in increasingly large packages. Although many consumers find 'value for money' important, it would be better to stop the emphasis of getting more food for you money. Smaller portion sizes can help you limit the amount of food you eat.

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Satiety enhancing food development: State of the art in the field of nutrition, food technology, consumer, marketing and technology

Developing foods that keep you feel full for longer is not a matter of simply adding extra fibers, water or air to a food. For many people, the signs of fullness that their body is giving them after eating are easily overridden by the temptations in our environment that trigger to continue eating. Think of the high visibility of delicious foods and large, convenient portion sizes. They all have substantial influence on the amount of food we eat and the resulting satisfaction.

Satiety is a complex interaction of physiological, social and psychological mechanisms.

Food providing enhanced satiety will have to function in the life of people surrounded by cues that stimulate excessive eating. This requires an integrated approach between various food-related disciplines.

This month, our new paper has been published: 'Successful development of satiety enhancing food products: Towards a multidisciplinary agenda of research challenges'. The paper presents the state of the art and key research challenges around satiety enhancings foods in the field of nutrition, food technology, consumer, marketing and communication.

My co-authors are Hans van Trijp, Joost van den borne and Charon Zondervan. Just click on the Critical Reviews in Food Science and Nutrition-paper below to read it full-text.

 

Do increased serving bowl sizes influence how much we eat?

It is often stated that that the increasing size of food portions is a strong factor contributing to the incidence of overweight and obesity. Numerous studies have shown it again and again: larger portion sizes, serving devices and packages lead people to eat more, often without them realizing it. In particular, individual serving devices such as plates, spoons and bowl have been shown to influence food intake. However, what has not been shown is whether the most central focus of the dinner table, the main serving bowl, has a similar magnifying effect. When one is eating at home and eating out in buffet restaurants, food is often available in serving bowls from which individual portions are distributed.

This month, the paper 'Serving bowl biases the amount of food served' I wrote together with Mitsuru Shimizu and Brian Wansink came out in the Journal of Nutrition Education and Behavior. This paper reports our study in which we wanted to determine how serving bowls filled with food for many persons influence serving behaviour and consumption. We expected that the larger the size of a multiple-serving bowl, the more people will serve and consume. In the study, 68 participants were randomly assigned to a group serving pasta from a large-sized bowl (almost 7 litre capacity) or a medium-sized bowl (almost 4 litre capacity). When given a large bowl, diners served 77% more pasta compared with the diners serving from the medium-sized bowl. They ate more, even though the food was not rated tastier or otherwise notable different.


Bowl size matters, so fill your largest bowl with salad



We wondered about the reasons for our findings. It could be that more 'social' reasons inhibit an individual from taking too much food from a smaller common bowl. Perhaps people use the size of serving bowl filled with food for multiple persons as an indication of how much they can best serve themselves. It could even seem greedy to take more food from a smaller bowl.

In any case, small increases in food intake may lead to substantial additional caloric intake over a longer time period and even weight gain. Just like larger package sizes, large serving devices seem to suggest to people that large portions are appropriate to consume.

These findings again highlight the role that external cues play in food consumption and show the importance of considering serving bowl size in nutrition education. Maybe our findings can be used to turn bad habits around; just put your salad in bigger bowls.

Are you thinking too much or too little about food?

I came across a really good paper of Dan Ariely and Michael Norton about the fascinating research being done in human decision making: 'From thinking too little to thinking too much: a continuum of decision making'.

Basically, there are two approaches to thinking; on the one end of the extreme someone is thinking too much and too carefully. On the other end of the extreme someone is thinking too little; a thinking style based on intuition, heuristics and quick short cuts. Both thinking too little and too much can have negative consequences and lead to mistakes, they argue.


More ice-cream options is definitely better... 

Thinking too much makes decisions harder or leads to postponing them. They refer to the famous study of Iyengar and Lepper who showed that grocery shoppers who were offered free samples of 24 jam flavors were less likely to buy any jam at all than those shoppers who sampled only 6 flavors. This clearly shows that considering too many options made it too hard to choose one. Barry Schwartz calls this 'the paradox of choice. Why more is less' and argues that we are faced with far too many choices on a daily basis. Nevertheless, Iyengar and Lepper's study also showed that people given more options enjoy the process of choosing. That is what I recognize when looking at my daughters in an Italian gelateria. They love to take their time to make a decision, although they typically end up with the same familiar strawberry flavour.

Dieters tend to think a lot about eating, particular negative self-thoughts. Their long history of going on and off on diets and guilty thinking patterns makes them more likely to overeat when confronted with tempting foods. Clearly an example of thinking too much, with harmful consequences. That is because their thinking is too 'concretely' and too much about the struggles of the moment ('shall I take the apple or the chocolate cake?). This uses up a lot of self-control in contrast to thinking about long-term goals (such as being fit and healthy) which can enhance your self-control. This finding came out of a study of Fujita and Han in Psychological Science.

Relying on habits ('I have always done it in this way') can be harmful as well. For example, out of habit, people tend to eat the entire portion that is served to them, even when it is stale popcorn. A little bit more thought could be good in that case. In other words, you may miss out opportunities to eat healthier when you often make quick decisions out of habit.

In an interview, Norton concludes by saying: 'What we know now is that people sometimes think too much, and sometimes they think too little. But we still don't know the right amount to think for any given decision, which is a fascinating decision yet to be solved.'

Snacking: what to do with the fourth meal of the day?

Snacking now constitutes 25% of calories consumed in the US, according to a study that was presented at the Institute of Food Technology meeting last month. This is about 580 calories per day, about the same size as a meal, according to professor Richard Mattes of Purdue University.

Why? There are more situations in which we are confronted with tempting food. Our internal hunger and satiety signals are weak, particularly when looking at large assortments of delicious treats. Refusing would require quite some self-control. What does not help, is that self-control is like a muscle in your arm, according to the well-known psychologist Roy Baumeister and his 'self-control-as-a-muscle-theory'. When used too intensively, it gets tired and is more likely to fail. Baumeister came up with the term 'ego depletion' to indicate that self-control is a limited resource. So the more you try to not give in to temptations the more likely you are to go for the 'forbidden' food in the end. Coupled with increased snack portion sizes available, it is not surprising that people get overweight. I guess there are two basic solutions: don't snack or snack smarter.

1)      Just do not snack 
When I was at Cornell last year, Jan Chozen Bays gave a very inspirational workshop about mindful eating. Mindful eating is paying full attention to eating without negative judgments. It is about being aware of physical and emotional sensations when eating. What struck me most during this workshop is that she said that we could learn to accept an empty stomach. It does not need to be filled immediately. Like Buddha, listening to the ebb and flow of hunger and desire, she explained. We are not used to that anymore, conditioned that we should not accept that nagging hungry feeling in our stomach. This reminded me of an old Dutch commercial with the slogan: 'Four o'clock: cup-a-soup, more people should do that'. Mindful eaters, however, do not look at the clock to decide what and when to eat, but listen closely to what their body is saying. Unfortunately, I still not that far in mastering the art of mindful eating...

Accept the 'four o'clock' feeling without snacking? (Still Cup a Soup commercial 1990s)

2)      Smart snacking: cut up your food 

You could switch to healthier foods, such as fruits. Another solution and probably more realistic for many of us is to cut up your food into smaller portions (maybe an interesting nudge?). David Marchiori and colleagues (see Journal of the American Dietetic Association) gave a group of study participants unlimited consumption from a bowl of candies. About half of the participants received candies that were cut in two pieces and the other half got the normal sized candies. Participants with the tiny candies ate about half compared to the other group. Although this was only a 60 calories difference, it showed that consumers typically view their consumption in numbers ('oh, I already had 5 candies) rather than quantities ('e.g. a handful). 

A related idea is to package your snacks in small-sized portions. A recent study of the Food and Brand lab gave one group of participants one large 400-calorie package of crackers and another group four smaller 100-calorie packs of the same crackers to eat during a television show. Results show that only overweight participants consumed more than double the number of calories when eating from the bigger package (384 calories versus 176 calories). Interestingly, all participants underestimated the number of crackers eaten. So, it is not the tracking of calories that is easier with a smaller package. Apparently, overweight people are more likely to rely on external cues (such as the need to open a new package) to stop eating, according to Wansink and colleagues.