A-Level Psychology: Comprehensive Notes on Eating Behavior

Evolutionary Explanations of Food Preferences

• Evolution is defined as the biological process by which species gradually adapt to their environment over many generations. Random gene mutations that provide a survival advantage become more widespread as they aid in the survival and reproduction of the species.
• Evolutionary psychology explains human food preferences as adaptations to ancestral environments:
  • Sweet Foods: These are typically high in energy. Ancestrally, consuming sweet foods allowed individuals to store energy as fat, which reduced the risk of starvation during periods of food scarcity.
  • Bitter Foods: Often, a bitter taste in nature indicates that a plant or substance is poisonous. Humans evolved a natural aversion to bitter tastes as a defense mechanism to avoid ingesting toxins.
• Neophobia: This is an innate dislike or fear of foods that an individual hasn't tried before. From an evolutionary perspective, this protected ancestors from potentially poisonous or unhealthy substances. Neophobia can be overcome through learning or repeated exposure.
  • Birch et al. (1987): Found that repeated exposure to unfamiliar foods can eventually reduce neophobia in children.
• Taste Aversions: This occurs when an individual develops a strong dislike for a specific food after becoming ill after eating it.
  • Biological Preparedness: Proposed by Seligman (1971), this theory suggests that humans are biologically predisposed to learn associations between certain stimuli (like food) and negative outcomes (like illness) very quickly to ensure survival.

Social and Learning Explanations of Food Preferences

• Social Influence and Prenatal Development: A child's food preferences begin to form in the womb. The nutrients and flavors from the mother's diet are passed to the baby through the amniotic fluid and later through breastfeeding. This early exposure shapes the child's later preferences.
• Social Learning Theory (SLT): Children observe the eating behaviors of parents and other role models. By imitating these models, children learn which foods are safe to eat, which helps reduce neophobia.
• Operant Conditioning: This playing a role in food consumption when enjoying a food acts as a positive reinforcement. This reinforcement increases the likelihood that the individual will choose to eat that food again, although it may not be the primary cause of the preference itself.
• Cultural Influence: Cultural background significantly dictates eating behaviors and rules regarding food.
  • Religious Restrictions: Certain religions forbid specific foods, such as Judaism forbidding pork or Hinduism forbidding beef.
  • Cultural Delicacies: Food availability and tradition vary by region; for instance, snails are common in France and raw octopus is a staple in Korea, whereas these are less common in regions like the UK.
• Applications: Understanding these factors is useful for child-rearing and for health agencies to tailor nutritional offerings to specific cultural populations.

Neural and Hormonal Mechanisms in Eating Control

• The Hypothalamus: The primary brain region responsible for maintaining homeostasis, including the regulation of body temperature, sleep, and hunger.
• The Dual-Center Model of the Hypothalamus:
  • Lateral Hypothalamus (LH): Known as the "hunger center," it is responsible for triggering the sensation of hunger and the initiation of eating. When blood sugar levels are low, the liver sends signals to the LH, causing neurons to fire.
  • Ventromedial Hypothalamus (VMH): Known as the "satiety center," it is responsible for making an individual feel full. Once food is consumed and glucose is released into the blood, the VMH detects this and triggers neurons that make the individual feel satiated.
• Hormonal Regulation:
  • Ghrelin: A hormone secreted by the stomach into the bloodstream when it is empty. It is detected by the hypothalamus and signals hunger. Once eating begins, the stomach stops releasing ghrelin.
  • Leptin: A hormone secreted by fat cells into the bloodstream. It signals to the hypothalamus that energy stores are high and that eating should stop. If an individual does not eat for a long period, fat deposits are used for energy, fat cells shrink, and leptin production ceases, leading to hunger.

Biological Explanations of Anorexia Nervosa

• Anorexia Nervosa: An eating disorder characterized by an obsession with weight loss, body image distortion, restricted food intake, and a dangerously low body weight.
• Genetic Factors:
  • Holland et al. (1988): Conducted a twin study and found a concordance rate of $56\%$ for identical (MZ) twins and only $5\%$ for non-identical (DZ) twins.
  • Bulik et al. (2006): Analyzed $31,000$ pairs of Swedish twins and estimated the heritability of anorexia at $56\%$.
  • Gene Association Studies: Comparing DNA profiles of sufferers versus controls has identified candidate genes such as $OPRD1$, $HTR1D$, and $EPHX2$.
• Neural Factors:
  • Individuals with anorexia often show reduced blood flow to the Lateral Hypothalamus, though it is unclear if this is a cause or an effect of the disorder.
  • Nunn et al. (2011): Proposed that damage to the orbitofrontal cortex is a key cause.
  • Serotonin: Kaye et al. (2009) hypothesized that patients have elevated serotonin activity which causes chronic anxiety. Starvation is used as a mechanism to reduce serotonin levels and alleviate this anxiety.
  • Dopamine: Bailer et al. (2013) suggested that an overproduction of dopamine may contribute to the disorder.

Psychological Explanations of Anorexia Nervosa

• Family Systems Theory: Proposed by Minuchin (1978), this psychodynamic theory suggests anorexia results from family dysfunction. Families of sufferers often exhibit four traits:
  • Enmeshment: No clear individual identities; the family functions as a single, blurred unit.
  • Overprotectiveness: High levels of control and protection.
  • Conflict Avoidance: The family avoids addressing disagreements at any cost.
  • Rigidity: The family structure is inflexible and resistant to change.
• Autonomy and Control: Bruch (1978) suggested that anorexia is a way for a young person to assert autonomy and gain control over their life in a rigid family environment.
• Social Learning Theory (SLT):
  • Modeling: Patients observe and imitate role models (siblings, celebrities).
  • Vicarious Reinforcement: Observing role models being praised or rewarded for being thin provides motivation to restrict eating.
  • Media Influence: Gossip magazines and social media often scrutinize celebrity weight gain, reinforcing the idea that slimness is the only desirable state.
  • Dittmar et al. (2006): Provided research support for the role of social learning in body dissatisfaction.
• Cognitive Explanations:
  • Distortion: Inaccurate perception of body image, potentially leading to body dysmorphia.
  • Irrational Beliefs: Maladaptive thoughts, such as "Eating one biscuit will make me instantly obese."

Biological and Psychological Explanations of Obesity

• Obesity: A condition of excess body fat leading to health issues like heart disease and diabetes. In the UK, approximately $30\%$ of the population is classified as obese.
• Biological Explanations:
  • Genetics: Stunkard et al. (1990) studied twins raised together and apart. Concordance for those raised together was $74\%$ for males and $69\%$ for females. For those raised apart, it was $70\%$ for males and $66\%$ for females, suggesting a heavy genetic influence.
  • FTO Gene: Fallon and Ingelson (2012) found the $FTO$ gene correlates with obesity, though it increases risk rather than acting as a direct cause.
  • Neural Factors: Damage to the Ventromedial Hypothalamus or neurons failing to respond to leptin can lead to overeating.
  • Dopamine: Volkow et al. (2008) found obese individuals often have reduced dopamine receptor activity, requiring them to overeat to feel pleasure.
  • Serotonin: Ohia et al. (2012) found lower serotonin levels correlate with obesity.
• Psychological Explanations:
  • Boundary Model: Herman and Polivy (1984) proposed that people have biological boundaries for hunger and fullness. The space between these is the "zone of biological indifference" where psychological factors dominate.
  • Restraint Theory: Attempting to severely restrict food can paradoxically lead to overeating. Once a self-imposed "restraint boundary" is crossed, eating becomes disinhibited, leadging to a binge until the individual is far beyond the biological fullness limit.

Success and Failure of Dieting

• Success Factors:
  • Realistic Expectations: Sustainable, steady weight loss over months and years.
  • Incentives and Motivation: Rewarding oneself for reaching milestones (operant conditioning).
  • Social Support: Having friends or family support the diet (Wing and Jeffrey, 1999).
  • Relapse Prevention: Developing new habits rather than returning to old eating patterns after the weight is lost.
• Failure Factors:
  • Overly Restricted Diets: Eating too few calories (e.g., only $1000$ per day) or extreme fasting.
  • Unrealistic Expectations: Trying to lose significant weight in a very short window (e.g., "the eight-week holiday diet").
• Research Bias: Much of the research into dieting and obesity is gender-biased, focused primarily on female participants, meaning findings may not apply identically to males.