Introduction to Eating Behaviour: Anorexia and Obesity
Welcome to this chapter on Anorexia Nervosa and Obesity. In this part of the AQA course, we look at the two ends of the eating behaviour spectrum. We will explore why some people develop a drive for extreme thinness and why others may struggle with excessive weight gain. We'll look at these through two main lenses: biological (our genes and brain) and psychological (our families, our thoughts, and our environment).
Don't worry if some of the theories seem complex at first! We will break them down into simple steps. Think of this chapter as a detective story where we try to find the "why" behind these behaviours.
Part 1: Anorexia Nervosa (AN)
Anorexia Nervosa is characterized by a refusal to maintain a healthy body weight and an intense fear of gaining weight. Here is how Psychology explains it:
1. Biological Explanations of AN
Genetic Explanations: Evidence suggests that AN runs in families. Researchers use twin studies to look at concordance rates (the likelihood that if one twin has it, the other does too). If identical (MZ) twins have a higher rate than non-identical (DZ) twins, it suggests a genetic link. Some estimates suggest the heritability of AN is between \( 50\% \) and \( 80\% \).
Neural Explanations: This focuses on neurotransmitters—the chemical messengers in the brain. Example: Serotonin is linked to anxiety and obsessive behaviour. Many people with AN have altered serotonin activity, which might lead to the perfectionism and anxiety associated with the disorder. Dopamine is also involved, particularly in how we feel "rewarded" by food. People with AN may have a different "reward" response to eating.
2. Psychological Explanations: Family Systems Theory
This theory suggests that AN is not just about the individual, but about the family unit. According to this view, the family "functions" in a way that contributes to the illness. There are three key concepts you need to know:
Enmeshment: Family members are overly involved in each other's lives. There are no clear boundaries. The child feels they have no privacy or individual identity.
Autonomy: Because the family is so enmeshed, the child struggles to become independent (gain autonomy). They feel "smothered" by their parents.
Control: In a family where every other part of life is controlled by parents, the child discovers that the only thing they can truly control is their food intake. Refusing to eat becomes a way to exert power and show they are an individual.
3. Psychological Explanations: Social Learning Theory (SLT)
SLT suggests we "learn" eating disorders from our environment through modelling and reinforcement.
Modelling: A person observes a role model (like a parent or a celebrity) who is very thin or constantly dieting. If that role model is someone the person identifies with, they are likely to imitate the behaviour.
Reinforcement: If a person loses weight and receives compliments like "You look great, have you lost weight?", this is positive reinforcement. Vicarious reinforcement happens when we see others being rewarded for being thin (e.g., a famous model getting fame and money).
Media: The media often portrays the "thin ideal." Constant exposure to these images can lead people (especially young women) to internalize the idea that "thin equals successful."
4. Psychological Explanations: Cognitive Theory
This focuses on dysfunctional thought processing. People with AN often have:
Distortions: This is a "glitch" in how they perceive reality. For example, they may look in a mirror and see themselves as overweight even when they are dangerously thin (body image distortion).
Irrational Beliefs: These are "all-or-nothing" thoughts. Example: "If I am not thin, I am a total failure" or "If I eat one biscuit, I will never stop gaining weight."
Key Takeaway for AN: AN is rarely about "just food." It is a complex mix of genetics, brain chemistry, family dynamics, social pressure, and distorted thinking.
Part 2: Obesity
Obesity is defined by having a Body Mass Index (BMI) of \( 30 \) or above. Like AN, it has both biological and psychological roots.
1. Biological Explanations of Obesity
Genetic Explanations: Obesity tends to run in families. Twin studies show that weight is highly heritable. However, it is polygenic, meaning it is caused by many different genes working together rather than just one "fat gene."
Neural Explanations: The brain's reward system might be different in people with obesity. Some people may have fewer dopamine receptors, meaning they need to eat more food to get the same "happy feeling" or reward that others get from a small amount.
2. Psychological Explanations: Restraint Theory and Disinhibition
This is often called the "Dieting Paradox."
Restraint Theory: Paradoxically, trying to restrain (limit) what you eat can lead to obesity. When people diet, they become highly preoccupied with food. This makes them more vulnerable to overeating.
Disinhibition: This is the "What the Hell" effect. A restrained eater has strict rules about what they can't eat. If they break a rule (e.g., eat one slice of pizza), they feel they have "blown it." They lose their inhibitions (disinhibition) and eat everything in sight. "I've ruined my diet anyway, so I might as well eat the whole pizza."
3. The Boundary Model
Proposed by Herman and Polivy, this model explains how "restrained eaters" (dieters) differ from "unrestrained eaters."
The Zones: We have a biological hunger boundary (when we feel we need food) and a satiety boundary (when we feel full). In between is the "Zone of Biological Indifference," where we don't feel particularly hungry or full.
The Difference: Unrestrained eaters eat until they reach the satiety boundary (they feel full). Restrained eaters set a "dietary boundary"—a mental limit on how much they will eat. This boundary is lower than the satiety boundary. The Problem: If a restrained eater crosses their dietary boundary, they experience disinhibition and continue eating past the satiety boundary until they are physically uncomfortable. This is why dieting often leads to weight gain over time.
Key Takeaway for Obesity: Biology plays a role in how we process food and rewards, but psychological "rules" like dieting often backfire and lead to overeating through the Boundary Model.
Common Mistakes to Avoid
1. Confusing "Neural" with "Hormonal": While they are related, "neural" refers to the brain and neurotransmitters (like serotonin). Make sure you keep them distinct if a question asks for a specific one.
2. Thinking SLT is just about the media: While media is a part of SLT, don't forget the importance of modelling from parents and direct reinforcement (compliments).
3. Misunderstanding the Boundary Model: Remember that the "dietary boundary" is a mental rule, while the "satiety boundary" is a biological signal. Obesity often involves the mental rule being broken.
Quick Review Quiz
Q1: What term describes a family where members are overly involved and boundaries are blurred? (Enmeshment)
Q2: In the Boundary Model, what happens when a dieter crosses their mental "dietary boundary"? (Disinhibition / The "What the Hell" effect)
Q3: Which neurotransmitter is most commonly linked to the obsessive thoughts found in Anorexia? (Serotonin)
Q4: True or False: SLT suggests that anorexia is purely genetic. (False - SLT is a psychological explanation focusing on learning and environment)
Great job! You have now covered the essential explanations for Anorexia Nervosa and Obesity for the AQA Psychology Paper 3.