The Reward System and the Epidemic of Obesity
A recent review by Rajita Sinha and Ania Jastreboff from the Yale Stress Center, New Haven, CT, USA, provides an integrative perspective on the neurohormonal mechanisms by which stress affects the reward system, and how the interactions between the stress and reward systems may contribute to the epidemic of obesity.
In spite of the well-known link between stress and obesity, the nature of this association remains poorly understood, including why is it some people lose weight when stressed, whereas others gain weight?
Animal research indicates that stress in most cases is related to a reduction in food intake. Interestingly, in rats, when given a choice of highly palatable food, such as lard or sugar, stress, in fact, increases intake of that palatable food. In humans, most individuals increase their food intake during stress yet a much smaller number of people, roughly 30%, are able to reduce food intake and lose weight during or after stress (cf. TC Adam & ES Epel, Physiol Behav, 2007, 91: 449).
In addition, an increasing body of evidence indicates that the brain reward circuitry may play a major role in stress-induced food intake (TC Adam & ES Epel, Physiol Behav, 2007, 91: 449). Furthermore, hedonic systems in brain influence food intake and excessive consumption of palatable food can trigger neuro-adaptive responses in brain reward circuitries similar to drug abuse (PJ Kenny, Neuron, 2011; 69: 664).
As with drug abuse, palatable food can activate the brain reward system, comprising opioid, dopamine and endocannabinoid signaling. This, in turn, produces a powerful behavioral reinforcement for both acquisitions of drugs as well as palatable food (TC Adam & ES Epel, Physiol Behav, 2007, 91: 449).
In their review Drs. Sinha and Jastreboff sum up recent research indicating the involvement of brain reward regions in obesity. They discuss how stress and glucocorticoids potentiate dopaminergic transmission, while stress-induced release of orexigenic neuropeptide Y (NPY) and the increased NPY messenger RNA expression in the hypothalamus, amygdala, and hippocampus increase feeding but also decrease anxiety and stress.
These overall changes increase food craving, motivation and intake of highly palatable (HP) foods. Thus, stress has been reported to increase binge eating and the consumption of fast food, snacks, and calorie dense and HP foods. In addition, the craving for desserts, snacks, and higher HP food intake, particularly, in overweight individuals and/or obese women increase as well.
The authors suggest a heuristic model of how HP foods, food cues, and stress exposure through alterations of metabolic, stress, and reward-motivation pathways in the brain are able to drive increased HP food motivation and intake. This includes:
- Stress- and metabolic- related hormones influencing brain reward regions and prefrontal cortical circuits involved in reward prediction, self-control, and decision making;
- With weight-related adaptations in neurohormonal and behavioral responses, a vulnerable individual becomes highly susceptible to food cues-related and stress-related HP food craving, predicting HP food intake;
- Promotion of weight gain, and increased sensitization of brain motivation pathways, to raise HP food motivation and intake, exceptionally under conditions of food cue or stress exposure.
The authors conclude that despite some advances in behavioral and pharmacological obesity treatment, it is unclear how they relate to normalizing stress, metabolic, and reward disturbances in susceptible obese individuals.
This research is in its infancy, but given the current world-wide obesity epidemic, it may require greater attention in the future.
Source: Biol Psychiatry, 2013, 73:827-35. doi: 10.1016/j.biopsych.2013.01.032. Epub 2013 Mar 26.
Read More: Biol Psychiatry
Updates
2015
In 2015 David F Marks introduced the homeostatic theory of obesity or the ‘Circle of Discontent’ theory. This is based on the theory and term homeostasis, invented by Walter Cannon. By this term he referred to the stability of the inner world.
According to David Marks homeostasis maintains equilibrium at set-points using feedback loops for optimum functioning of the organism. Thus, in this new theory, homeostatic obesity imbalance is attributed to a hypothesized ‘Circle of Discontent’, a system of feedback loops linking weight gain, body dissatisfaction, negative affect and over-consumption.
In 2016 Rachel Annunziato and Stephanie Grossman indicated that the homeostasis theory focuses on five feedback loops that form an insidious and vicious “Circle of Discontent”. If, for any reason, high levels of dissatisfaction, negative affect, consumption, or increased body weight should arise, then interactivity through feedback loops creates a vicious circle, a disturbance to the stability of the system that controls weight gain. When it becomes activated, the system drifts away from equilibrium toward a dysfunctional state of non-control.
2016
In a 2016 commentary David Marks proposed that when eating control is overridden by hedonic reward, a condition of obesity dyshomeostasis occurs. The breakdown of homeostasis causes disorders that include obesity, as well as addictions and chronic health conditions including stress in persons with diverse body shapes. All such conditions entail the self-reinforcing activity of a vicious the Circle of Discontent (COD). Hedonic reward overrides weight homeostasis to produce obesity dyshomeostasis (OD).
According to David Marks appetitive hedonic reward is a natural response to an obesogenic environment containing endemic stress and easily accessible and palatable high-energy foods and beverages. Obesity dyshomeostasis is mediated by the prefrontal cortex, amygdala and hypothalamic–pituitary–adrenal (HPA) axis. The ghrelin axis provides the perfect signaling system for feeding dyshomeostasis, affect control and hedonic reward. Dyshomeostasis plays a central role in obesity causation, the addictions and chronic conditions and in persons with diverse bodies.
2017
A 2017 study by Selin Neseliler et al. was based on the perception that psychosocial stress is associated with an increased intake of palatable foods and weight gain in stress-reactive individuals, and that personality traits predict stress-reactivity.
The authors reported that the effects of real life stress on appetitive brain function and self-control is modulated by a personality trait. This may help to explain why stressful periods can lead to overeating in vulnerable individuals.
2022
A 2022 study by Jason Bini et al. was the first to demonstrate that single acute overnight administration of glucocorticoids at physiological levels akin to acute life stress resulted in increased fasting hunger and decreased perfusion in regions of the brain which regulate reward-motivation, homeostasis, taste and flavor perception/interoception, emotion-memory, and executive function.
Also, the authors reported that glucocorticoids significantly decreased whole brain voxel based cerebral blood flow responses in the hypothalamus and related cortico-striatal-limbic regions, while increased hunger, glucose, insulin and leptin.
The investigators concluded that their study suggested that increased glucocorticoids at levels akin to those experienced during psychological stress, may result in increased fasting hunger and decreased regional cerebral blood flow in a distinct brain network of prefrontal, emotional, reward, motivation, sensory and homeostatic regions that underlie control of food intake.
2025
A 2025 opinion paper by Paulina Jankowska discussed the psychological mechanisms linking stress and obesity, highlighting several key mechanisms by which stress and mental health influence obesity in adults, notably through stress-induced eating and impaired emotional regulation.
According to this author, chronic stress can lead to overeating of unhealthy comfort foods, reduced self-control, and lifestyle patterns that favor weight gain, whereas emotional distress can push individuals toward food as a coping mechanism and interfere with healthy habits.
Thus, the author concluded that psychological stress and poor mental health can drive behaviors and biological responses that significantly contribute to weight gain and make weight management more challenging.
At the same time, living with obesity can generate additional stress and psychological strain, creating a self-perpetuating cycle. Breaking this cycle requires recognizing that obesity is not solely a matter of willpower or caloric balance, but also of managing stress and emotional well-being.
“People may very well choose to trade off years of their life,
or the possibility of disease or injury,
in exchange for the current pleasure, excitement,
or stress relief they get from food”
Jacob Sullum
Cover Image Credit: (Left panel) Brain Structures Involved in the Reward System. From Telzer (2016). Adapted with permission from Elsevier. Downloaded from: https://www.ncbi.nlm.nih.gov/books/NBK576548/box/ch2.b3/?report=objectonly
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