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

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.

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.

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.