Introduction

 

Obesity has risen to become a global health problem with more than 500 million obese individuals worldwide [3].  Within Scotland, the Scottish Health Survey revealed that 35% of adults are overweight and 29% are obese [1].  As obesity predisposes people for multiple serious conditions including heart disease, stroke, cancer, and type II diabetes, it becomes highly relevant to better understand the reasons behind weight gain.  If weight gain is fundamentally a result of energy imbalance (i.e. increased energy intake and decreased energy expenditure), then becoming overweight could simply be solved with restoring this balance (i.e increased physical activity and calorie restriction).  However, research shows that only 25% of overweight people are actually successful at maintaining weight loss, defined by intentionally losing 10% or more of initial weight and keeping the weight off for at least 1 year [6].  This alarming statistic indicates that weight loss and more importantly weight loss maintenance, are more complex.  This article will function to highlight the homeostatic, environmental and behavioural mechanisms that drive weight regain following weight loss.

3 Factors Influencing Weight Regain

Homeostatic 

 

The body is regulated by a number of biological systems that maintain it in homeostasis, defined by a physiological sate of equilibrium [3].  A part of the brain, located at the base, called the hypothalamus, plays an important role in maintaining the body in homeostasis [5].  In addition to helping in the role of hormone release, the hypothalamus influences weight regulation by creating a “set point” for weight gain [4].  A “set point’ can be described as a specific, ideal body weight that body maintains for optimal functioning.  Much like a temperature thermostat, the body adjusts food intake and/or energy expenditure up and and down in proportion to its current body weight to maintain itself at its “set point” weight [4].  

Recent research demonstrates the hypothalamus receives signals from hormones from fat tissue that provide information about energy and fat stores [7]. A primary hunger hormone, discussed in a previous blog post, called leptin, communicates with the hypothalamus about fat mass [4].  Like a thermostat, the hypothalamus responds to signals from leptin by increasing energy expenditure and decreasing energy intake to regulate weight gain. For example, under conditions of excess food intake, leptin will release from fat cells to communicate with the hypothalamus to increase energy expenditure and lower food intake [7].

 

The hypothalamus also communicates signals from the cortio-limbic system, a network in the brain that process a broad range of cognitive and behavioural functions [4].  Within this pathway exists sensory systems responsible for sight, smell and taste [3[.  The cortico-limbic system together with the hypothalamus can be conceptualised as the core processor that controls appetite [4].  As the incentive to consume food is driven by both hunger and hedonic (pleasure) preferences, highly palatable, calorie-dense foods have been shown to increase the responsiveness of the cortico-limbic system and motivation state to consume these foods [5].  This increased hedonic reward from consuming calorie-dense foods further enhances the desire to consume these types of foods [5].  The result is a hedonic pathway that overrides the body’s homeostatic control leading to excessive food intake and ultimately weight regain.

Environment 

 

The dramatic rise in obesity in industrialised countries and high rates of weight regain parallel the increasingly “obesogenic” environment we live in.  This environment includes intense promotion of low-cost, energy-rich foods, considerably larger portion sizes, and increased accessibility and availability of such foods [3].  Collectively, these factors greatly challenge self-control and cognitive reasoning that consequently challenge homeostasis [2].    

Moreover, the modern environment contributes to heightened physiological stress that induces overeating [3].  Stress-induced eating has become somewhat of a disorder whereby in response to negative emotions, individuals over consume on energy-dense foods for comfort or self-medication [2].  Stress can then create an emotional connection between an individual and food and promote weight regain via the hedonic pathway.  

Evidence of the potential damaging environmental effects of energy-dense foods on weight regain were demonstrated by Kilgore and colleagues (2013). In their study, the authors used 38 subjects (22 male; 16 female) with low normal to Stage 1 obesity and had them undergo food imaging tasks under functional neuroimaging (fMRI) [5].  Subjects were exposed to visual images of various food and non-food items for 30 seconds that alternated between high-calorie foods (i.e cheeseburger) to low-caloric foods (i.e fruits), to non-food items (i.e. flowers). [5].     

Subjects were then asked to rate “how much would you like to eat each item right now?”  Results showed that visual cues to high-calorie foods heightened the cortico-limbic response in women meaning greater motivation to consume the highly palatable foods [5].  This response was found to be greatly predictive of body mass index suggesting that weight gain in women may be caused by a greater responsiveness of food motivation when exposed to high-calorie foods [5]. 

Behavioural 

 

It is evident that simply knowing exercise and healthy eating will prevent weight regain is not enough for reducing excess body weight [3].  While it is clear that environmental factors influence weight regain and obesity, the daily behaviours or actions an individual employs should not be undermined as contributing factors. The research identifies multiple obesity-promoting behaviours that can contribute to weight regain.  These include frequent consumption of high-calorie dense foods and sugary drinks, large portion sizes, and skipping breakfast, all of which contribute to overeating.  Likewise, low levels of physical activity and sedentary behaviour are further identified as weight regain and obesity risk factors [8].  

A study by Wilkie and colleagues (2016) found that reduced sleep and more time spent watching television and using the computer were positively associated with weight regain and obesity [10].  The increased use of technological devices, collectively referred to as “screen time,” plays an important role in promoting sedentary behaviour in modern day living [10].  Also, it has been well established that television watching specifically promotes high-calorie food consumption and creates further exposure to advertisements of calorie-rich foods [10]. 

Engaging in successful behaviours to prevent weight gain becomes challenging in the face of strong environmental cues. Promoting self-efficacy, a belief that someone can successfully engage in a behaviour, has been highlighted as being an important pre-curser to creating and applying healthy behaviours like exercise [3].  A number of studies have identified common behavioural patterns among individuals who successfully maintained weight loss.  These behaviours include physical activity, regular self-monitoring of body weight and food intake, flexible dieting strategies, selecting lower calorie foods, and planned meals in advance [9].   

Summary 

 

As weight gain and obesity in Scotland and across most westernised countries continue to rise, we are able to identify a complex interaction of homeostatic, environmental and behavioural factors that underpin weight regain following weight loss.  Homeostatic regulation is challenged by powerful hedonic reward pathways that influence our food decision making and reward [3].  Similarly, the role of the environment contributes to weight regain through the promotion of high-calorie foods, high-stress eating, sleep debt, and increased screen time.  Finally, behavioural patterns like consuming large food portions, selecting energy-dense foods, and maintaining a sedentary lifestyle all function to promote weight gain and make weight loss extremely challenging.  Coaching strategies require specific attention to each of these three areas to overcome challenges to weight regain. 

 

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References 

[1] Baker, Carl. 2019. House of Commons Library. Obesity Statistics. No. 3336, Pg.15. August. [Online] Taken From: www.parliament.uk/commons-library | intranet.parliament.uk/commons-library 

[2] Berthoud, H. R. et al. 2017. Blaming the brain for obesity: Integration of hedonic and homeostatic mechanisms. May. Issue.152, No.7, 1728-1738. Gastroenterology.

[3] Greenway, F. L. 2015. Physiological Adaptations to Weight Loss and Factors Favouring Weight Regain. No.39, pp.1188-1196. International Journal of Obesity.

[4] Keesey, R. E. et al. 1997. Body Weight Set-Points: Determination and Adjustment. September, Vol.127, No.9, pp.1875S-1883S. The Journal of Nutrition. 

[5] Killgore, W. D. S. et al. 2013. Cortico-limbic Responsiveness to High-Calorie Food Images Predicts Weight Status Among Women. Vol.37, pp.1435-1442. International Journal of Obesity. 

[6] Milsom, V. A. et al. 2011. Successful Long-Term Weight Loss Maintenance In A Rural Population. Vol.6, pp.303–309. Clinical Intervention Ageing.

[7] Muller, M. et al. 2010. Is There Evidence For A Set Point That Regulates Body Weight? August. No.2, pp.59. F1000 Medicine Reports.

[8] Rennie, K. L. et al. 2005. Behavioural Determinants of Obesity. September. Vol.19, No.3, pp.343-358. Best Practice & Research Clinical Endocrinology & Metabolism. 

[9] Varkevisser, R. D. M. et al. 2019. Determinants of Weight Loss Maintenance: A Systematic Review. February. Vol.20, No.2, pp.171-211. Obesity Review. 

[10] Wilikie, H. K. et al. 2016. Multiple lifestyle behaviours and overweight and obesity among children aged 9–11 years: results from the UK site of the International Study of Childhood Obesity, Lifestyle and the Environment. Vol.6. Issue 2. British Medical Journal Open. 

[11] Wing, R. R. 2011. Successful Weight Loss Maintenance. Annual Review of Nutrition. No.21,pp.323-341.