Almost two-thirds of UK adults are on a diet most of the time, but are diets even worth it? What’s the psychology behind dieting? This article will explore why people go on diets and what is behind successful versus unsuccessful dieting.
Fig. 1 - Diets remain popular in our society; with most adults almost always dieting, we need to understand what makes diets work.The Diet Definition
Dieting comes in many forms; it can involve cutting out particular food groups, such as dairy or sugary foods, or controlling one’s caloric intake to create a deficit.
Diets often involve cognitive patterns such as categorising food, planning and thinking about food intake.
By studying the psychology behind dieting, we can see why this may or may not work for different individuals.
Dieting is where a person intentionally restricts their food intake to achieve a goal such as weight loss or improved health.
Explanations for the Success and Failure of Dieting Psychology
Several psychological models have been proposed to explain why many diets fail in the long term. These models include:
- The spiral model.
- Ironic process theory.
- Locus of control effects.
- Hedonic theory.
Let’s explore and evaluate these models’ explanations of dieting success and failure.
Psychology Behind Dieting: The Spiral Model
Polivy and Heatherton (1992) proposed the spiral model of dieting. Accordingly, dieting behaviours create a ‘downward spiral’ in which it becomes harder and harder to lose weight despite the diet becoming ‘stricter’.
The spiral model indicates that dieting is motivated by comparison to an ideal self, which leads to body dissatisfaction and dieting to achieve one’s ideal physique.
Positive outcomes initially reinforce dieting behaviour but eventually, dieting leads to psychological and physiological changes that make it harder for chronic dieters to lose weight.
This behaviour tends to start in adolescence, when individuals first begin experiencing negative thoughts about their bodies, leading to insecurity.
Insecurity leads to their first attempt at a restrictive diet, which often produces some small tangible results, making the dieter feel this restriction is an effective way to control their weight.
Initial success at weight loss encourages further dieting. However, when the individual regains the weight, as most dieters do, they are likely to ‘try again’, resuming their diet usually with stricter rules and eating even less.
Lasting weight loss due to restrictive dieting is rare, and each failed diet attempt increases frustration, dissatisfaction, and distress, which prompts further and often stricter dieting. Stricter dieting is likely to result in failure and disinhibition, and the cycle repeats.
Disinhibition occurs when an individual loses control over their food intake.
Periods of dieting can also cause physiological changes in how our body communicates signals of satiety and hunger through hormones like ghrelin.
Evaluation of the Spiral Model
A strength of the spiral model is that it has useful applications.
For example, by instilling better self-esteem in adolescence, we can prevent young people from beginning the downward spiral of restrictive dieting.
Also, by educating young people on how unlikely restrictive dieting is to yield any long-term results, we can help them avoid long-term negative health consequences like weaker bones, higher susceptibility to disinhibition, and low self-esteem.
A criticism of the spiral model is that it does not address the issues that lead to low self-esteem, which starts this spiral in the first place.
Yoger et al. (1988) found that dieters who give up their restrictive diets can often turn to substance abuse as they have not addressed the self-esteem issues that lead them to diet in the first place.
Psychology Behind Dieting: Ironic Processes Theory
Another explanation for why diets fail is Daniel Wegner’s theory of ironic processes. The theory proposes that diets fail because restriction makes individuals preoccupied with food.
Participants were asked, “Don’t think about a white bear” in the Wegner et al. (1987) study. The study found almost all participants thought of a white bear, even more than those specifically asked to think of one.
For people on diets, the same effect may occur when trying not to think about the foods they’ve restricted; i.e. they would be much more likely to become preoccupied with those foods.
Constantly thinking about ‘forbidden’ foods makes individuals more susceptible to disinhibited eating, which causes them to consume more calories and gain more weight.
Fig. 2 - Food restriction can result in a preoccupation with food, contributing to diet failure.
Evaluation of the Ironic Processes Theory
Adriaanse et al. (2011) supported the ironic processes theory. In this study, a group of female students tried to reduce their intake of chocolate and crisps and had negative views on diets, for example, ‘When I am sad, I will not eat chocolate’. These negative statements were associated with higher amounts of ‘forbidden’ food consumption.
However, it is unclear how their food intake would be affected by diet intentions in the long term.
Psychology Behind dieting: Locus of Control
A term first coined by Julian Rotter in 1954, a person’s locus of control is how much or little control they believe they have over their life. Two types of locus of control are known as ‘internal’ and ‘external’.
Internal locus of control is when an individual believes they are the ones in control of the trajectory of their life and what happens to them. (e.g., If I study, I will do well on my exam).
External locus of control is when an individual believes that external factors and other people control the trajectory of their life and what happens to them (e.g. I’ll only do well in my exam if the questions are fair).
People with an internal locus of control may be more likely to succeed in their efforts to diet than those with an external locus of control. This is because they have more perceived control over adhering to the diet.
Evaluation of the Locus of Control
The locus of control explanation is limited by how it is studied. Most studies investigating this theory use self-report questionnaires to determine the participant’s locus of control. This can lack validity as self-report methods are often subject to demand characteristics and social desirability bias.
Psychology Behind Dieting: Hedonic Theory
According to the hedonic theory, diets fail because restriction makes people respond stronger to foods in their environment.
The hedonic theory states those who engage in restriction can become more sensitive to hedonic eating behaviours. It means that their eating behaviours can become motivated by pleasure rather than just physiological hunger.
Moreover, decreased sensitivity to feedback from the body (satiety or hunger) that helps us regulate our weight can make dieters more prone to overeating and weight gain.
When the environment is food rich, and the need to eat is driven by pleasure rather than the need to survive and consume calories, hedonic eating is at odds with the goal of homeostasis (eating just for satiety).
Evaluation of Hedonic Theory
Evidence supporting the hedonic theory is that the salivary activity in restrained eaters is greater than in non-restrained eaters. This suggests that restrained eaters are more sensitive to the pleasure aspect of eating.
Brunstrom et al. (2004) measured participants’ saliva levels before and after exposure to a hot pizza (desirable food) before and after they had lunch.
The smell of this food pre-lunch produced a higher salivation response in restrained eaters than non-restrained eaters.
Fig. 3 - Diets can increase one’s sensitivity to the pleasure of eating.
What is the Relationship Between Diet and Obesity?
Due to the physiological and psychological changes resulting from dieting, the question of whether diets are linked to weight gain or obesity arises.
One reason dieting can paradoxically lead to weight gain is that dieting reduces our sensitivity to internal cues of hunger and fullness.
The restraint theory argues that exerting cognitive control over one’s food intake, so eating according to the diet, not the signals from our body, can make dieters vulnerable to disinhibition.
This is because once they lose touch with their internal cues, they can have difficulty stopping eating once they’re full.
Disinhibition is also linked to the all-or-nothing theory. These two concepts have been illustrated in the Herman, Polivy & Esses (1987) study.
Dieters and non-dieters were given either no food, a milkshake, or a double milkshake before being given ice cream. The researchers measured how the amount of food they were given before ice cream impacted the amount of ice cream they consumed.
- Non-dieters: the more food this group consumed before having ice cream, the less ice cream they had.
- Dieters: the more food this group consumed before having ice cream, the more ice cream they had.
This study shows that dieters are more likely to experience disinhibition once they break some diet rules.
Diet and Psychology: What Makes Diets Successful?
Based on the psychological theories outlined above, we can identify several features that can make diets more successful. Some features like easing the restriction can also mean that the diet won’t bring immediate weight loss results, but they might reduce the episodes of disinhibition that many dieters experience.
Theory | What can make diets more successful? |
The spiral model | Avoiding the restriction-disinhibition cycle by not increasing restriction after “failing” and allowing flexibility in one’s diet |
Ironic processes theory | Decreasing restrictions to alleviate preoccupation with food |
Locus of Control | Moving towards an internal locus of control. More perceived control over diet adherence can potentially increase one’s success |
Hedonic Theory | Decreasing restriction and allowing flexibility in one’s diet to reduce physiological responsiveness to food |
Restraint Theory | Honouring the body’s internal cues of hunger and fullness |
All or Nothing Theory | Avoiding all-or-nothing thinking by allowing flexibility in one’s diet |
Psychological Effects of Dieting
According to the spiral model, dieting is likely to fail due to the nature of how restriction results in physiological changes and disinhibition. A failed dieting attempt has psychological consequences; it increases frustration, guilt, dissatisfaction and distress, which prompts further and often stricter dieting.
As predicted by the Ironic Process Theory, diets affect the extent to which individuals are preoccupied with food. Dieting can increase the frequency of thinking about food and make it difficult to focus on anything else.
Diets can also change how we think about food.
The moment dieters break the restriction rule, they are more likely to experience disinhibition and episodes of eating beyond their satiety.
One reason for this is all-or-nothing thinking. Food can also become much more appealing and pleasurable to dieters because it is seen as a scarce resource.
All-or-nothing thinking involves losing control over one’s food intake after breaking restriction rules. The dieter either adheres to the diet completely or eats large amounts of foods that they are restricting.
Psychology behind Dieting - Key takeaways
- The diet definition is where a person intentionally restricts their food intake to achieve a goal such as weight loss or improved health.
- Several psychological models have been proposed to explain why many diets fail in the long term. These include the spiral model, ironic process theory, locus of control effects and hedonic theory.
- Diets can result in negative emotions, preoccupation with food, disinhibition, and changes in how food is perceived.
- The link between restriction and disinhibition emphasised by the restraint theory and the all-or-nothing theory can explain why diets can result in weight gain.
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