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.
 

Interview Professor Paul Rozin: Why we have to change people's world if we want them to eat better

Retiring this year, but still busy doing research. Inspired by the way musical pieces often start out slow, build up and then climax, he enthusiastically talks about a new project. 'People come up with a summary judgement of how good a meal is. We are looking at the degree to which an ending is important. You put the best things at the end. People like things that rise', he explains a new study.

In December, I am invited to stay at the Centre For Advanced Studies at the Norwegian Academy of Science and Letters. Every year, this centre hosts three parallel research groups organized around a central theme. One theme of this year is 'The ecology of food perception'.  Researchers from Norway and abroad are invited to work together for several months. Paul Rozin is also invited and I visited him during his stay. He is a professor of psychology at the University of Pennsylvania. Paul Rozin is considered to be one of the most influential researchers on human food choice and particularly known for his work on the meaning of disgust.

We talked about working with Brian Wansink ('We have similar attitudes towards things and we are both outliers'), journals' bias to only publish positive results ('That is ridiculous') and pressure to publish or follow a particular model of how to do research. 'The basis question one should ask is how much the contribution adds to understanding', he writes in his 2009 paper in Perspectives on Psychological Sciences. In this paper, Paul Rozin talks about the value of moving from top-down hypothesis testing as dominant research model in many top psychological journals to research approaches that lead to broader generalizations of interesting phenomena. ''What they do is that they find something with a set of experimental parameters and then instead of saying 'Is this real?', 'Can I change the parameters a bit and is it still there?', they go ahead, they analyse it and they go down. That is what a journal wants', he said. Exploring the large picture of a phenomenon is key according to him; 'Even in the lab, you can vary your parameters. A parameter that you think is not critical, often is in real life'.

We went on to talk about obesity ('We plateaued, I think it is because we now drink more bottled water') and interventions that could help people to eat better. When I asked his opinion on Herman and Polivy's argument that not much progress has been made so far in combatting the obesity problem and that it is probably easier to make the case that things are getting worse, he strongly agrees. 'I think they are right. They are very smart people, they worked on this for decades. I have said that but I do not know whether I said it in print. Nothing has been shown to work except maybe bariatric surgery', he said.

This may seem a pessimistic view, but Paul Rozin has clear ideas about possible solutions. He is a believer of the nudge approach: 'I do not think that we can change people. I think we have to change their world. That is what I think has happened in France. Their world is different, the way their food is presented is different. That is why they have half our obesity rates. I cannot proof that, there are too many variables. That is encouraging, that their environment is so different and they are much thinner.'

Paul Rozin, however, is not yet convinced about the long-term potential of nudging: 'There is no question that it works in the short run. What we do not know is whether nudging will work in the long run. We know that it works over a week, but we don't know whether it works over a year, because there may be compensation in various ways. Doing a year's study will involve a lot of investment. You have to get too many people to support you', he said. An interesting perspective of Professor Paul Rozin; a leading expert you should definitely continue to follow.

Stealth Health - Guiding healthier eating in stores and schools: Presentation Brian Wansink at Wageningen University

Last week, Brian Wansink presented his latest nudging studies at Wageningen University. In one of the presented studies, consumer participants in a grocery store were nudged by changing their shopping cart. The nudge was not particularly high tech: Brian and his team put a line of duct tape across the width of the shopping cart and a sign 'put your fruits and vegetables here'. These changes to the shopping cart made consumers purchase more fruits and vegetables without affecting total sales. Have a look yourself.

Brian visited our Marketing and Consumer Behaviour group, because Evelien van de Veer defended her thesis 'Relying on satiety cues in food consumption: studies on the role of social context, appearance focus, and mindfulness'. Brian was opponent in her thesis committee. Read a interesting summary in Dutch of Evelien's thesis in the Resource.

Debunking fast food: How expectations shape our eating experiences

When I was at the Food and Brand lab at Cornell University, the crew of Penn and Teller (well-known US TV show) filmed a small-scale consumer experiment. They invited a food designer known for doing 'extreme makeovers' with fast food (see his blog 'Fancy Fast Food'). This designer changed the fast food bought at places like KFC, McDonalds and Dunkin' Donuts into beautifully looking restaurant dishes.

Then the experiment started. Visitors of the lab were tricked into believing they were eating fancy restaurant food. As a result, the food was highly liked. 'It is something my grandma would make', one guy told. Then a second experiment started. Here, one group was correctly told that the salad they were served came from the fast food chain Taco Bells. Not surprisingly, the response was accordingly: 'Big, greasy and maybe not so healthy'. However, when exactly the same salad was presented as coming from the 'California Garden Cafe', people were much more enthusiastic ('It's good... it's light').

We like to believe that we are experts in recognizing excellent cooking. In reality, how we experience food is not only determined by the characteristics of the food itself, but at least as much by our expectations, desires and beliefs. If we think that a food or drink is going to taste good, we look for positive qualities that confirm that belief and justify our choice. This is related to the health halo effect, which refers to consumers' tendency to think that when a food possesses one desirable feature ('freshly made'), the food is automatically assumed to have more desirable features ('it tastes light'). A risky bias, which may lead to underestimating how many calories we actually eat.

Watch this video, it is really fun. By the way, I am not in the video, I was washing the dishes...