What is the debate?
It is questionable which factors influence the success and failure of dieting.
Outline boundary theory
According to Boundary Theory (Herman and Polivy), the success and failure of dieting is controlled by two boundaries. Non- dieters generally eat until their biological boundary, when CCK signals satiety in the ventromedial hypothalamus. Eating beyond this causes discomfort. Instead, successful dieters routinely eat until their cognitive boundary, which a self-imposed limit of how much they think they should eat to lose (or maintain) their weight. However, often, if a dieter eats beyond their cognitive boundary they will experience the "what the hell" effect, where they become disinhibited, eating until (or even beyond) their biological boundary. In this case, they are likely to be unsuccessful in their dieting.
Research evidence for boundary theory
Convincing evidence for the role of Boundary Theory in the success of dieting comes from Herman and Mack, who found that high-restraint dieters given no pre-load ate the smallest amount of ice-cream of all other participants, whereas dieters who received a pre-load (of a milkshake) ate the largest amount of ice-cream of all groups. The first finding gives evidence for the cognitive boundary in the success of dieting, as dieters felt able to resist eating too much ice cream whilst their cognitive boundary was intact. However, the second finding gives evidence for the role of the "what the hell" effect in the failure of dieting, as they became disinhibited, eating more ice cream than they normally would because the pre-load had caused them to already surpass their cognitive boundary.
evaluation of research and boundary theory
However, undermining its support for Boundary Theory, Herman and Mack's research can be criticised for its lack of internal validity. As it asked participants to eat quantities of food outside of their typical daily routine, the research may not have successfully measured what was intended. Even so, adding weight to the theory, a strength of Boundary theory it that it is interactionist as it considers both biological and cognitive factors in its explanation of human eating behaviour. This is because it argues that we use both cognitions about how much we think we show eat and neural mechanisms of how much we have actually eaten to determine feelings of satiation, suggesting it may well add to the success of dieting.
Outline Ironic Processes of Thought Control
Alternatively, according to the Ironic Processes of Thought Control (thought suppression), this is the processes that causes us to fail in dieting. It states that when we are specifically asked not to think about something, we ironically cannot help but think of that thing. For example, when asked not to think of a white bear, participants reported that they couldn’t help but think of a white bear. The same happens to dieters who wish to turn their attention away from food.
Research evidence for Ironic Processes of Thought
Convincing evidence to support the role of the Ironic Process of Thought Control in the success and failure of dieting comes from Sotens who asked dieters not to think about food and found that participants has more thoughts about food after the though-suppression task. This shows that we often fail at dieting as the more dieters wish to turn their attention away from food the more thoughts they have, meaning they are more likely to relapse (fail). On the other hand, contradicting this, the role of though suppression in the failure of dieting can be criticised for being unfalsifiable and unscientific because it is impossible to objectively test people's cognitions about their dieting behaviour. As a result, the theory is also speculative because it makes assumptions that go beyond the findings of research, meaning we can only speculate about people's thoughts.
Outline stomach capacity and desensitiation
Finally, according to the Stomach Capacity and Desensitisation theory, the success and failure of a diet is due to the boundary's the individual holds. Most people generally eat until their biological boundary, when CCK signals satiety in the ventromedial hypothalamus. Eating beyond this boundary becomes punishing due to the bloating of the stomach. However, if an individual consistently overeats, they are likely to become de-sensitised to the feelings of satiation, meaning they increase their stomach capacity overtime and more food is required to feel full. The opposite is true for those who consistently under-eat. Therefore, individuals who consistently over eat will need to stop this behaviour in order to succeed at dieting, whereas those who reduce their stomach capacity will succeed because they are able to feel satiated much more quickly.
Evidence for stomach capactiy and desensitisation
Strong evidence for the role of stomach capacity and desensitisation for the success and failure of dieting comes from Robinson who scanned the stomachs of 22 anorexic and non-anorexic participants. He found that the anorexics had smaller stomachs and reported feelings of satiation more quickly than non-anorexics. Additionally, compelling evidence also comes from Stacher, who studied 12 underweight anorexics by giving half of the group a drug which artificially reduced feelings of satiations and the other half a placebo for a period of six weeks. When participants stopped receiving their medication, those in the drug group reported reduced feelings of satiation at meal times, and gained weight more quickly than the placebo group. This shows that it is possible to be successful in healthy dieting by eating less (causing a shrinking of the stomach), reducing the capacity in order to feel satiation. It is also possible to be unsuccessful in dieting if you consistently overeat causing a stretching of the stomach and causing a bigger capacity of food to be required to feel full.
What is the conclusion?
Therefore, it is clear that Boundary theory and Stomach capacity and to a lesser extent Thought Suppression are extremely important to be successful within dieting.