Background

Achieving sustained decreases in energy (food) intake is key to maintaining healthy weight and combating overweight and obesity. Our work shows that there is no tight physiological control of energy balance. While this underlies our vulnerability to overeating, it also means that it’s possible to reduce our food intake without experiencing irresistible hunger. Many of our projects capitalise on this basic principle.

Example publications:

• Rogers, P. J., & Brunstrom, J. M. (2016). Appetite and energy balancing. Physiology & Behavior, 164, 465-471. Click here to read.   
• Rogers, P. J., Ferriday, D., Jebb, S. A., & Brunstrom, J. M. (2016). Connecting biology with psychology to make sense of appetite control. Nutrition Bulletin, 41(4), 344-352. Click here to read.

NIHR Bristol Biomedical Research Centre

The NBU is a workstream lead in the  NIHR Bristol Biomedical Research Centre in Nutrition, Diet and Lifestyle. The workstream aims to improve metabolic control in people with type 2 diabetes. Our primary collaborator is Julian Hamilton-Shield, who is a Paediatrician and Professor of Diabetes and Metabolic Endocrinology.

1. We are exploring how hypoglycaemia (low blood sugar levels) impact food preferences and cognition. This understanding can guide development of strategies for managing hypoglycaemic episodes. Our work includes laboratory-based studies with adults and testing at the Clinical Investigation Unit of the Bristol Royal Hospital for Children.
2. WELMID is a weight-loss maintenance intervention for people living with type 2 diabetes. It focusses on equipping individuals who have completed a weight loss programme with detailed knowledge on how appetite and weight control work, and strategies that can help them overcome obstacles to sustained weight maintenance.
3. Using virtual reality as a research tool, Sarah Sauchelli Toran is studying the complex relationship between the personal experience of physical activity and how this impacts subsequent food intake. Can we help sedentary adults to avoid rewarding themselves with food after completing a workout?

Intermittent fasting

In recent years, intermittent fasting diets such as the 5:2 Diet, alternate day fasting and time-restricted eating have grown in popularity. For example, the 5:2 Diet requires individuals to restrict their caloric intake for two days of the week (500 calories/day for women or 600 calories/day for men) while eating normally for the remaining five days.

Intermittent fasting diets have been associated with beneficial health outcomes. In addition to weight loss, they have been associated with reduced risk of cancer and cardiovascular disease, as well as improved insulin sensitivity. One idea is that intermittent fasting has become popular because it is easier to maintain over long periods. We have been exploring whether this is the case and why.

Current research: Becca Elsworth (Ph.D. student) has been working with Jeff Brunstrom (primary supervisor), Julian Hamilton-Shield, Elanor Hinton, and Natalia Lawrence to explore why the experience of fasting might have long-term benefits for healthy weight maintenance. One of their questions is whether a single fasting episode can promote a change in personal beliefs about hunger and perceived need to eat regularly throughout the day. To test this idea, they are using ecological momentary assessment (EMA) to capture daily patterns in appetite. EMA involves repeated real-time sampling of an individual’s current appetite and dietary behaviour (using a mobile device). More generally, they are also investigating how appetite status/sensations influence the portions that people select and the foods that they choose.

Previous research: A few years ago, Becci Griggs and Christina Potter (two former Ph.D. students), began to address questions about intermittent fasting. Becci used the diet as a platform to understand the impact of expectations about hunger and eating on dietary behaviour and reactivity to food. Christina identified some of the perceived physiological and psychological barriers to fasting and showed that they predicted dieting success.

Over 1,000 volunteers have participated in our intermittent fasting research studies, from diverse backgrounds and with varied weight and dieting statuses, greatly enhancing our understanding of the psychology behind the success of these diets.

Example publications:

• Potter, C., Griggs, R. L., Brunstrom, J. M., & Rogers, P. J. (2019). Breaking the fast: Meal patterns and beliefs about healthy eating style are associated with adherence to intermittent fasting diets. Appetite, 133, 32-39. Click here to read.
• Griggs, R. L., Potter, C., Rogers, P. J., & Brunstrom, J. M. (2016). Intermittent fasting: not as hungry as you expected? Appetite, 100(101), 224. Click here to read.

Food cue reactivity

In the late 1960s, Stanley Schachter developed a highly influential proposal that became known as the ‘externality theory of human obesity’. This theory argues that the obesity (and overeating) occurs because people vary in their sensitivity to hunger and satiation cues, and some are more sensitive to external cues, including the sensory characteristics of food.

It is now well established that food-cue exposure (exposure to the sight or smell of food) can have a powerful effect on appetite. Even brief exposure to the sight and smell of food can initiate a ‘cephalic phase responses’ (the release of insulin, changes in salivation, heart rate, gastric activity, and blood pressure), and an increase the amount of food that people plan to consume.

Our work has helped to show how these responses vary across individuals, and how sensitivity to food cues can impact dietary behaviour.

Example publications:

• Ferriday, D & Brunstrom, JM 2011, 'I just can't help myself: effects of food-cue exposure in overweight and lean individuals' International Journal of Obesity, vol 35, pp. 142 - 149. Click here to read.
• Ferriday, D & Brunstrom, JM 2008, 'How does food-cue exposure lead to larger meal sizes?' British Journal of Nutrition, vol 100, pp. 1325 - 1332. Click here to read.
• ESRC Project: “Individual differences and food-cue reactivity: Predictors of BMI, portion size, and everyday dietary behaviour.” Click here to view.