Welcome to the psychological explanations for obesity! While biological theories focus on genetics and neural mechanisms, psychological explanations look at how our thoughts and behaviours around food can unintentionally lead to weight gain.

What you'll learn:

• How attempting to restrict food intake can paradoxically lead to overeating (Restraint Theory).
• Why breaking a diet rule often triggers a total loss of control (Disinhibition).
• How biological urges and cognitive rules interact to cause binge eating (The Boundary Model).
• How to evaluate these theories using key studies and methodological criticisms.

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Restraint Theory

Common sense suggests that going on a strict diet is the best way to lose weight. However, restraint theory, developed by Herman and Polivy (1975), suggests the exact opposite: trying to lose weight by placing strict cognitive limits on food intake can actually cause you to eat more.

When someone becomes a restrained eater, they spend a significant amount of time thinking about food. They must constantly categorise foods into "good" and "bad" or track their calories. Because they are ignoring their natural physiological signals (hunger and fullness), they rely entirely on their willpower.

This creates a state of psychological preoccupation. The restrained eater is highly sensitive to food cues, which makes them vulnerable to losing control.

Disinhibition

If restraint theory explains the setup for obesity, disinhibition explains the trigger.

Because restrained eaters ignore their biological satiety (fullness) signals, their eating is entirely controlled by their mind. If that mental control slips, there is nothing left to stop them from eating.

Triggers for disinhibition can be internal or external:

• Internal cues: Emotional distress, anxiety, or low mood.
• External cues: The smell of baking, social situations, drinking alcohol, or being exposed to media images of food.

The most common trigger is simply breaking the diet slightly. If a restrained eater eats a single slice of cake, they feel they have crossed their cognitive limit. This triggers the "what the hell" effect (or all-or-nothing thinking). Because the rule is already broken, the diet is "ruined" for the day, so they disinhibit and eat everything in sight.

The Boundary Model

Herman and Polivy (1984) developed the Boundary Model to tie restraint and disinhibition together. It explains how biological and cognitive factors interact in eating behaviour.

According to this model, eating is regulated along a continuum from hunger to satiety (fullness).

• At the bottom of the continuum is the biological hunger boundary. When we drop below this, we feel physical discomfort and are strongly motivated to eat.
• At the top is the biological satiety boundary. When we go above this, we feel uncomfortably full and stop eating.
• The gap between these two biological boundaries is called the Zone of Biological Indifference. In this zone, we are neither starving nor stuffed. We eat (or don't eat) based on social, cultural, and cognitive factors.

As the diagram shows, a restrained eater's boundaries look very different from a normal eater's:

1. A wider zone of biological indifference: Because restrained eaters frequently ignore hunger and push past satiety during binges, their biological boundaries become stretched. It takes them longer to feel hungry and longer to feel full.
2. The Cognitive Diet Boundary: Restrained eaters insert a self-imposed "diet boundary" inside their zone of biological indifference. This represents the maximum amount of food they permit themselves to eat.

Evaluating Psychological Explanations (AO3)

When evaluating these theories, you need to look at both the supporting research and the theoretical limitations.

Strengths and Supporting Evidence

Experimental support: Wardle and Beales (1988) provided strong evidence for restraint theory. They randomly assigned 27 obese women to one of three groups: a diet group (restraint), an exercise group, and a non-treatment control group. Over seven weeks, the women's food intake was assessed in laboratory conditions. In week four, all participants were given a "preload" (a high-calorie snack) before a taste test. The women in the diet group ate significantly more in the taste test than the other two groups. This clearly demonstrates that cognitive restraint makes individuals vulnerable to disinhibition and overeating.

Support from cognitive psychology: The failure of cognitive restraint can be explained by Wegner's theory of ironic processes of mental control. Wegner found that when you actively try not to think about something (like a white bear), you actually think about it more. By suppressing thoughts of food, restrained eaters make food more salient in their minds, increasing the likelihood of disinhibition.

Weaknesses and Limitations

Fails to distinguish between types of restraint: A major limitation of restraint theory is that it treats all dieting as identical. Researchers later identified two distinct types of restraint:

• Rigid restraint: An all-or-nothing approach to eating (which leads to the "what the hell" effect and obesity).
• Flexible restraint: A looser approach where individuals allow for occasional treats without feeling they have ruined their diet. Research suggests that flexible restraint often leads to successful weight loss, contradicting Herman and Polivy's blanket claim that restraint always causes weight gain.

Cannot explain all eating disorders: Restraint theory struggles to explain anorexia nervosa. Anorexic individuals exhibit extreme cognitive restraint, yet this does not lead to disinhibition and overeating. If restraint universally leads to bingeing, anorexia would not exist in its restrictive form.

Methodological issues: Much of the research into these psychological explanations relies on self-report measures, such as the Restraint Scale. These questionnaires are highly vulnerable to social desirability bias. Overweight individuals might under-report their calorie intake or over-report their dietary restraint to appear as though they are "trying" to lose weight, which damages the validity of the data.