Difficulty: Intermediate | Prerequisites: Intro to health psychology concepts (Exam 1 material)
Big picture: This section covers the psychological mechanisms behind why and how people eat, the major theories explaining obesity, and the role of exercise in health. It sits at the intersection of biological, cognitive, and social factors, which is a recurring theme across PSY 320. You should already be comfortable with basic biopsychosocial models from earlier in the course. Understanding these theories is essential because they reappear in discussions of body image, social class, and women's health later in Exam 2.
Psychologists explain eating behaviour through three main lenses: internal vs. external hunger cues, eating as mood regulation, and the self-defeating cycle of rigid dietary restraint. Obesity has multiple causes, from genetics and evolution to energy imbalance and short sleep in childhood. Personality traits (neuroticism, extraversion, low conscientiousness) are also linked to higher BMI.
Internal-external hypothesis (food reward theory)
The idea that eating is driven by two kinds of cues: internal signals (physiological hunger, satiety) and external signals (the sight or smell of appealing food). In simple terms, your stomach tells you one thing, but a fresh plate of chips in front of you tells you another.
Mood regulation (emotional eating)
Using food to influence emotional state, particularly to relieve stress or negative feelings. Stress eating is more commonly reported in women. Think of it as reaching for comfort food after a rough day, not because you are hungry, but because it makes you feel better.
Restraint theory
The observation that imposing rigid cognitive rules on eating ("I must not eat carbs") tends to backfire. Once the rule is broken, even slightly, the person abandons all restraint entirely. In simple terms, one slip leads to "I've already ruined it, so I might as well keep going."
Energy balance
The relationship between calories consumed and calories expended. Weight gain occurs when energy intake consistently exceeds energy output. Think of it as a simple accounting problem: more in than out means the surplus gets stored.
Evolutionary hypothesis (of obesity)
The theory that humans evolved to store fat efficiently during times of food abundance as a survival advantage during famine. In a modern environment with constant food availability, this once-adaptive trait contributes to obesity.
Developmental hypothesis (of obesity)
The idea that predisposition to being overweight can be detected as early as in the womb. Prenatal and early-life conditions may programme metabolic pathways that increase obesity risk later in life.
Internal-external hypothesis
Internal cues: physiological hunger signals from the body (stomach contractions, blood sugar drops)
External cues: environmental triggers such as the smell of food, seeing an attractive meal, or social pressure to eat
The theory explains why people overeat in food-rich environments even when not physiologically hungry
Mood regulation and emotional eating
People eat to change how they feel, not just to satisfy hunger
Stress eating is more prevalent in women than in men
This connects to broader health psychology themes about coping mechanisms and maladaptive behaviours
Restraint theory
Rigid cognitive rules about diet ("I will only eat 1,200 calories") create an all-or-nothing dynamic
When the rule is broken, the dieter abandons restraint entirely, often eating more than they would have without the rule
This is sometimes called the "what-the-hell effect" in the literature
Research has found that certain personality traits predict higher BMI:
Higher neuroticism (tendency toward emotional instability and stress)
Higher extraversion (sociability, which may increase exposure to social eating situations)
Lower conscientiousness (less self-discipline around health behaviours)
Genetic factors
Genes influence metabolism, fat storage, and appetite regulation
Obesity runs in families, though this reflects both shared genetics and shared environments
Evolutionary hypothesis
Natural selection favoured efficient fat storage when food was scarce
In modern environments with abundant, calorie-dense food, this creates a mismatch between biology and context
Energy balance
Weight gain is fundamentally about consuming more energy than the body uses
Calorie-dense, highly processed foods make it easy to tip the balance
Physical inactivity
Sedentary lifestyles reduce the "expenditure" side of the energy equation
Both occupational and leisure-time inactivity contribute
Developmental hypothesis
Obesity risk can be detected prenatally
Conditions in the womb (maternal nutrition, gestational diabetes) may programme the child's metabolism
Short sleep duration in childhood
Children who sleep fewer hours are at increased risk for obesity
Sleep deprivation affects hormones that regulate appetite (ghrelin and leptin)
Students often think the internal-external hypothesis says external cues are "bad." It does not. Both cue types are normal; the theory explains how external cues can override internal signals, not that they should never influence eating.
Students often assume restraint theory means all dieting is harmful. The theory specifically targets rigid, all-or-nothing cognitive rules. Flexible, moderate approaches to eating do not trigger the same rebound effect.
Students sometimes treat obesity as caused by a single factor (usually willpower or genetics alone). The exam material presents it as multifactorial: genes, environment, behaviour, development, and sleep all contribute.
Students sometimes conflate mood regulation with restraint theory. Mood regulation is about eating to change how you feel. Restraint theory is about what happens when rigid dietary rules collapse. They are related but distinct mechanisms.
Be able to distinguish the three psychological theories of eating (internal-external, mood regulation, restraint theory) and give an example of each
Know the six causes of obesity listed in the review and be prepared to explain each briefly
The personality-BMI link (neuroticism, extraversion, low conscientiousness) is a specific finding worth memorising
Restraint theory and the "what-the-hell effect" are commonly tested because they are counterintuitive
The developmental hypothesis is easy to overlook; know that obesity risk can begin in the womb
Body dissatisfaction and obesity statistics have cultural differences (connects to the statistics section of the exam)
True or False: Restraint theory predicts that strict dieting rules make people eat less overall. (False: they tend to cause rebound overeating.)
Fill in the blank: People with higher ______, higher extraversion, or lower conscientiousness tend to have higher BMI. (Neuroticism)
True or False: The developmental hypothesis states that obesity risk can be detected as early as in the womb. (True)
Fill in the blank: Eating to change how you feel is called ______ ______. (Mood regulation / emotional eating)
True or False: The evolutionary hypothesis suggests that fat storage was once an adaptive survival mechanism. (True)
Q: What is the internal-external hypothesis, and how does it explain overeating?
A: The internal-external hypothesis (food reward theory) proposes that eating is driven by internal cues (hunger signals from the body) and external cues (environmental triggers like smell or sight of food). Overeating occurs when external cues override internal satiety signals, leading people to eat when they are not physiologically hungry.
Q: Explain restraint theory and the rebound effect it predicts.
A: Restraint theory describes how imposing rigid cognitive rules on eating creates an all-or-nothing pattern. Once the person breaks the rule, even slightly, they abandon restraint altogether and often eat more than they would have without the rule. This rebound is sometimes called the "what-the-hell effect."
Q: Name three personality traits associated with higher BMI and explain the direction of each relationship.
A: Higher neuroticism, higher extraversion, and lower conscientiousness are each associated with higher BMI. Neuroticism contributes through emotional instability and stress eating; extraversion through greater exposure to social eating; low conscientiousness through reduced self-discipline in health behaviours.
Q: List four causes of obesity discussed in the course and briefly explain each.
A: (1) Genetic factors: inherited differences in metabolism and appetite regulation. (2) Evolutionary hypothesis: natural selection favoured fat storage for survival, which now contributes to obesity in food-abundant environments. (3) Energy balance: consuming more calories than the body expends. (4) Physical inactivity: sedentary lifestyles reduce energy expenditure. (Other valid answers: developmental hypothesis, short sleep duration in childhood.)
Q: How does mood regulation differ from restraint theory as an explanation for eating behaviour?
A: Mood regulation explains eating as a strategy to change emotional state (e.g., eating comfort food to relieve stress). Restraint theory explains eating as a consequence of rigid dieting rules collapsing. The first is about why someone eats; the second is about what happens when dietary control fails.
This material connects directly to the Social Class, Race, and Health unit because socioeconomic status influences access to healthy food, opportunities for physical activity, and exposure to stress eating. The obesity and body image content also ties into Women's Health (body dissatisfaction statistics, pregnancy weight) and Sexual Health (body image and sexual wellbeing).
Internal-external hypothesis, food reward theory, mood regulation, emotional eating, stress eating, restraint theory, what-the-hell effect, dietary restraint, obesity causes, energy balance, evolutionary hypothesis, thrifty gene, developmental hypothesis, foetal programming, BMI and personality, neuroticism, extraversion, conscientiousness, body dissatisfaction, childhood sleep and obesity, PSY 320, health psychology, Michigan State University, Exam 2