Nudge150: Combining small changes to foods to achieve a sustained decrease in energy intake

Lead Research Organisation: University of Bristol
Department Name: Experimental Psychology

Abstract

Achieving sustained decreases in energy (food) intake is key to maintaining healthy weight and combating overweight and obesity. This project combines two approaches to meet this challenge.
The first of these arises from the fact that there is not tight physiological control of energy balance. While this underlies our vulnerability to overeating, it also means that it is possible to reduce our food intake without experiencing irresistible hunger. It has been found that if people under-eat at one meal, they do not fully compensate with increased eating at subsequent meals. So, if we ate 150 kcal less at lunch every day for a year we might expect to eat 18,000 kcal (365 x 50 kcal) less over that year, which would help to prevent weight gain, or might even cause slight weight loss. This focus on reduced portion size is consistent with the UK Government's 'Responsibility Deal' and public health initiatives in other counties.

We will test the feasibility of this -150 kcal 'nudge' to eating behaviour in this project. We will also investigate the effectiveness of various additional small nudges to the foods we eat aimed at increasing the effectiveness and long-term acceptability of the reduced portion size nudge (perhaps leading to up to a spontaneous 100 kcal per day reduction in food intake). An obvious approach would be to try to increase the fillingness of foods, but this has been tried in a variety of studies and has met with limited success. Instead we will investigate ways to increase meal 'satisfaction' and test whether this helps to control appetite - our approach here is 'reward your appetite,' rather than 'feel fuller for longer.'

Accordingly, in the first phase of the research we will investigate whether, for example, increasing taste intensity, increasing food variety, and modifying food texture (e.g., creamy versus chewy) and unit size (e.g., same item presented in a larger number of smaller pieces) will enhance meal satisfaction and reduce subsequent appetite. In preliminary studies we will also invite consumers and food industry experts to comment on these approaches and help us generate other ideas to test.

We will also investigate the 'breakpoint' in portion size reduction; that is, at what point do people choose supplementary items or even two portions? We will develop a method to do this based on established principles used widely in the measurement of other human perceptual abilities.

In the second phase of the research we will compare the effect on subsequent appetite and energy intake of (1) a standard lunch, (2) a smaller portion of the same lunch (-150 kcal), and (3) a smaller lunch (also -150 kcal) combined with a blend of the most feasible and effective manipulations for increasing meal satisfaction. This will be done at the beginning and end of ten exposures (days 1, 3 and 10) to these lunches to test for possible adaptation effects that might reduce the effectiveness of these 'nudges' over time.

The impact of this research lies in the innovation testing the short and longer term effectiveness of the -150 kcal nudge, and in emphasising meal satisfaction as a promising way to aid sustained acceptance of (slightly) smaller portion sizes, thereby providing a route for the food industry to help implement a widely supported public health approach to weight management.

Technical Summary

Achieving sustained decreases in energy intake is key to maintaining healthy weight. This project combines two principles to meet this challenge.

The first is that there is not tight physiological control of energy balance. While this underlies vulnerability to overeating, it can also be exploited to assist in reducing energy intake. The second is that the (biological) reward value of food is derived from its nutrient content, and not the extent to which it causes fullness. Thus reducing portion size or energy density will devalue food. We will investigate ways to compensate for this devaluation, including increasing taste intensity and food variety, and modifying food texture.

In consultation with consumers and food industry experts we will prioritise five 'manipulations' and test their effectiveness in increasing eating enjoyment (and other measures of food reward) and meal satisfaction and in decreasing short-term energy intake. We will also measure eating topography and memory for the food eaten as possible mediators of the effects of increasing eating enjoyment. Successful manipulations will be blended for testing in an RCT.

Another potential problem with a portion size intervention is that the consumer may choose supplementary items or two portions instead of one. To address this we will develop and apply psychophysical methods to identify and quantify 'breakpoints' in consumer behaviour and decisions around portion size.

In the RCT we will test the hypothesis that reducing portion size by 150 kcal at lunch will reduce 24-hour energy intake (nudge group), and that addition of 'nudges' designed to maintain meal satisfaction will reduce energy intake still further (nudge+). We will also investigate the effects of repeated exposure to these nudges.

The focus on portion size is consistent with public health initiatives and proposes an avenue whereby industry can help by providing products that are lower in energy and accepted over the long term.

Planned Impact

The main beneficiaries for this research will be consumers (the general public), the food industry and policy makers.

Consumers who wish to maintain a healthy weight will benefit because the research promises to identify ways to reduce energy intake that do not compromise eating enjoyment, and that can be maintained over the long term.

The food industry will benefit because the research will underpin innovation in relation to sustained acceptance of reduced portion sizes. In doing so, it will provide industry with a route to implement a widely-supported public health approach to weight management. It will also develop tools for measuring portion size 'breakpoint' that will be used to investigate consumer tolerance to reduced portion size, and which industry could use in future product testing and development work.

For policy makers the research will help test and develop the notion that portion size reduction is a potentially achievable and effective approach to weight management, and therefore to preventing levels of overweight and obesity continuing to rise.

The research also has potential to improve the nation's health and wealth. This is because overweight and obesity and related disorders, such as Type 2 diabetes, have a significant negative impact on quality of life, and the associated health care costs and days work lost are a major economic burden to society.

The present research will also have impact by contributing to knowledge and understanding of human appetite control. In particular our contention that the difficulty of eating less has to do with being deprived of something that is rewarding rather than not feeling full is important theoretically and has important implications for designing strategies to reduce energy intake. By promoting this distinction between reward and fullness the present research promises to have a significant influence on the future direction of research on appetite control and thereby provide new insights into the problem of weight management.

Publications

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Description Data collection is complete on three studies investigating portion size 'break-point.' The data indicate that people can discriminate small differences in food portion size when products are compared simultaneously, but differences have to be significantly larger to be noticed when portion size judgements are based on memory - even when the different portions are presented closely in time. Furthermore, a person's usual food portion size biases their memory for standard and reduced portion sizes.

Further research investigated effects of portion size on meal satisfaction and subsequent eating. In a study varying portion size, we found that there was increased energy intake in partial compensation for reduced portion sizes (25% and 50% reduction) when participants were given the opportunity to continue the meal with a further offering of foods, but almost no such compensation when further eating was delayed for 2½ hours. This confirms the potential for reduced portion size to reduce overall energy intake. Together with the previous study, it also demonstrates the potential to reduce within meal compensation for smaller portion sizes by enhancing meal satisfaction. Accordingly, and after consultation with industry colleagues and consumers, the next two studies tested the effects of food variety, food segmentation (i.e., serving the foods divided into several small pieces vs single larger pieces) and flavour intensity on meal satisfaction and compensatory eating.

Neither food variety nor food segmentation were found to affect eating enjoyment or meal satisfaction, and they did not offset compensation for reduced portion size. However, enhanced flavour intensity significantly increased food liking and eating enjoyment and in turn helped to compensate for the decrease in meal satisfaction, resulting from decreased portion size, but these effects were only evident when the manipulation was accompanied by a menu card ('hedonic label') describing the enhanced flavour (i.e., 'Gourmet Ham and Cheese Sandwich. Gourmet Flapjack. The ingredients of this meal have been carefully selected to be especially flavourful'). Further studies demonstrated that food variety was also successful in increasing eating enjoyment when accompanied by the hedonic label. Increasing the apparent volume of food on the plate, via pasta shape and an aerated chocolate bar for dessert, was found not to significantly enhance fullness or meal satisfaction.

Accordingly, for our longer-term randomised controlled trial (RCT), we selected flavour intensity and food variety, supported by hedonic labelling, as the intervention to offset portion size reduction. This three-arm RCT compared the effect of a 600 kcal full portion (standard) at lunch, versus half-portion (Nudge), versus half portion with the flavour, variety and hedonic label enhancements (Nudge+). The primary outcome measure was daily energy intake, measured on days, 1, 3 and 10 of the intervention. The participants consumed their allocated lunch on 10 consecutive weekdays (two Monday-Friday weeks), attending our Nutrition and Behaviour Unit Laboratory on days one, three, and ten. On those days they received in the laboratory, breakfast, the test lunch, and dinner. In between meals, participants were free to return to their place of work or home, etc as appropriate. Between-meal snacks and beverages were given to participants to take away. In addition to energy intake, meal satisfaction, meal enjoyment, body weight and other psychological variables (such as liking and satiety) were measured. On day two and days four through nine, participants collected their lunch from our laboratory, to take away to eat.

Two key hypotheses were: (1) a 50% reduction in portion size at a single meal (lunch) will decrease total daily energy intake, and (2) the Nudge+ enhancements to the foods (increased variety and flavour intensity, accompanied by a hedonic label) will at least partially offset the reduced meal enjoyment and satisfaction that occurs with reduced portion size. Other work in this project demonstrated that meal satisfaction is determined primarily by meal enjoyment and the fillingness of the food consumed. With a smaller portion there is both less oral contact with food (leading to reduced enjoyment) and less food entering the stomach (leading to reduced fillingness). A further objective of the RCT was to test whether there is adaptation to repeated exposure to a reduced portion size resulting in, for example, increased compensatory eating from day 1 to day 10.

157 non-dieting participants, 95 women and 62 men, BMI=23.4 kg/m2, completed the trial (the target was 156). Participant characteristics were very well matched across groups. Mean daily energy intake 2893 kcal, which was similar to participants' mean estimated energy requirements (2768 kcal). Results for energy intake showed, contrary to our hypothesis, complete compensation (p=.010) for the reduced portion size for both Nudge and Nudge+ groups, due mainly to increased snack (p=.021) and dinner (p=.020) intakes. In other words, the 50% reduction in portion size at lunch did not reduce daily energy intake (p=.734). Degree of compensation did not vary over the 10 days. Analysis of the data on meal enjoyment, meal satisfaction, fullness, etc is ongoing.

Within the constraints of accurate measurement of energy intake, the study modelled naturalistic eating behaviour and meal patterns, which included the ready availability of snacks throughout the day. The latter, together with the high salience of a 50% smaller than typical sandwich lunch, may have facilitated energy intake compensation. Indeed, memory of having eaten a small lunch may well have been responsible for both the higher snack intake, and the higher dinner intake 5 hours later.
Exploitation Route The findings confirm the importance of portion size in determining energy intake and support the potential for compensating for loss of reward value of smaller portions. This could potentially help industry to reduce food portion size without compromising acceptability and repeat purchase of products. Nonetheless, the RCT showed that a large reduction in portion size at lunch had no effect on daily energy intake. From industry and public health perspectives this suggests that stealthier approaches, such as small reductions in portion size at multiple eating occasions and/or covert reductions in food energy density, should be prioritised in the endeavour to reduce daily energy intake.
Sectors Agriculture, Food and Drink,Healthcare

 
Description British Psychological Society "Psychology in the Pub" - Don't tell me you're hungry; it's just your excuse for eating too much 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact Professor Peter Rogers was invited to deliver a talk at one of the BPS "Psychology in the Pub" events. In this talk, he challenged a range of common beliefs about eating and presented his bathtub and saucepan model of human dietary behaviour. Attendants reported thoroughly enjoying the talk and reported that it stimulated changes in views, opinions and behaviour.
Year(s) Of Engagement Activity 2015
URL http://www.bristol.ac.uk/expsych/news/2016/109.html
 
Description Campden BRI innovation showcase 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Presentation of research project aims and current findings to industry and to academic researchers. Feedback indicated considerable interest in the approach being taken and led to new contacts between the project team and industry.
Year(s) Of Engagement Activity 2015
 
Description Industry/Academia dissemination event (organised by BBSRC DRINC) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Presentation of research project aims and current findings to industry and to academic researchers. Feedback indicated considerable interest in the approach being taken and contributed to ideas for the continuing research.
Year(s) Of Engagement Activity 2014,2015,2016,2017
 
Description Live experiment for AT-Bristol Science Centre 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact In collaboration with At-Bristol Science Centre colleagues conducted live experiment on eating behaviour, namely sensory-specific satiety for popcorn flavours. Audience/participants were adults attending 'After Hours' event. Results were updated as each participant completed their session, accompanied by live feedback and explanation of the study and the background science.
Year(s) Of Engagement Activity 2016
URL http://www.bristol.ac.uk/expsych/research/brain/nbu/news/2016/afterhours.html
 
Description Live research demonstration at Bristol Half Marathon 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact On Sunday 13th September 2015, thousands of runners took part in Bristol's 27th annual half marathon. Dani Ferriday, Duncan McCaig, and Christina Potter from the Nutrition and Behaviour Unit (NBU) were on site in Anchor Square to speak to interested members of the public about the group's research. Using an interactive demonstration, they discussed the meaning of the term 'calorie' and illustrated how our beliefs about the amount of fullness that a food will deliver ('expected satiety') are not based solely on the number of calories that a food contains but other factors as well. For example, they showed that foods that are more familiar to us and foods that are larger are expected to deliver more fullness even when they are presented in portions with an identical number of calories. There was a lot of interest from those who participated in taking part in further NBU research.
Year(s) Of Engagement Activity 2015
URL https://www.bristol.ac.uk/expsych/news/2015/266.html
 
Description Live tasting experiment in Anchor Square, Bristol 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Dr Ferriday and Dr Fielding conducted a live tasting experiment in Anchor Square, Bristol. The stall asked participants to taste and rate different varieties of flapjacks for various sensory attributes. These data were used to inform the choice of foods for a subsequent experiment in the Nudge150 project. After participating, participants were informed about sensory specific satiety, the variety effect and their effects on food intake.
Year(s) Of Engagement Activity 2016
 
Description Nudge150 research talk at Mondelez research facility in Reading 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Researchers from the Nudge150 project were invited to tour the Mondelez research facility in Reading and to provide a 20-minute oral presentation on the project and supporting research. Interested members of the research facility attended the presentation which sparked discussion on the research themes throughout
Year(s) Of Engagement Activity 2018
 
Description Nudge150 research talk at University of Bristol - Wageningen University seminar 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact PhD students from Wageningen University visited University of Bristol to find out more about our lab and our research. Dr Ferriday delivered a 30 minute research presentation of the Nudge 150 project and its associated findings. The talk generated discussions and requests for more information from interested postgraduate students.
Year(s) Of Engagement Activity 2017
 
Description Portion size conference (Liverpool) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Conference discussing food portion size research and its application. Participants included scientists, food industry and postgraduate students.
Year(s) Of Engagement Activity 2017
 
Description Stall at Food Matters Live 2016 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact More than 13,500 experts from across the food, health and nutrition sectors attended Food Matters Live 2016. The Nutrition and Behaviour Unit hosted a stall at this event and featured a Powerpoint projection which detailed current research projects/ideas, methodologies, facilities. Recent scientific publications were also available for distribution. This stall sparked interest, conversations and requests for further information.
Year(s) Of Engagement Activity 2016
URL https://www.foodmatterslive.com/
 
Description Talk on portion size and The Calorie Reduction Summit 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Talk on role of food portion size in influencing energy intake, and how to reduce portion size without affecting eating enjoyment. Panel discussion with other speakers and discussion with other conference attendees afterwards.
Year(s) Of Engagement Activity 2018
URL https://twitter.com/caloriesummit?lang=en-gb
 
Description Webinar on calorie reduction (for NutriWebinar) 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Webinar involving three experts in nutrition, eating behaviour and market research concerned with effective approaches to calorie reduction.
Year(s) Of Engagement Activity 2018
URL http://nutrilicious.co.uk/calorie-reduction-webinar/