Explanations for obesity
The genetic explanation sees obesity as having an inherited component, with several genes involved. The more of these you have, the more vulnerable you are to developing obesity. The neural explanation sees obesity as resulting from abnormally functioning brain mechanisms, with attention focused on the ventromedial hypothalamus, as well as the action of leptin upon the POMC and NPY neurones, due to their roles in regulating appetite. Restraint theory perceives obesity as resulting from the placing of unsustainable limits on food intake, which results in disinhibition where overeating and weight gain occurs due to the loss of restraint. The boundary model proposes that hunger motivates individuals to intake food above a set minimum level and that satiety (fullness) motivates individuals to keep intake below a set level. Obesity arises, because once restrained eaters exceed their self-imposed eating target, they continue to eat to satiety, as their physiological set-point boundary overrides the self-imposed cognitive boundary. Diets fail due to being unsustainable, setting unrealistic targets, loss of motivation and hunger pangs. Diets succeed when weight is lost in an attainable manner and a stable energy balance is achieved around a new lower weight. Social support helps, as does positive reinforcements for achieving weight loss targets.
Fig 13.4 Can obesity be explained by biological or psychological explanations?
Stunkard et al. (1990) assessed the role of genetics in the development of obesity. The researchers compared body mass similarities between twins in a sample of 154 pairs of MZ (identical) twins who had been reared together, 93 pairs of MZ twins who had been reared apart, 208 pairs of DZ (non-identical) twins who had been reared together and 218 pairs of DZ twins who had been reared apart. If obesity had a genetic component, then MZ twins should have a higher concordance rate for obesity than DZ twins. Twins reared apart aroused special interest, as they would not have experienced identical environmental influences. It was found that the highest concordance rate for obesity was between MZ twins reared together, but MZ twins reared apart (0.68 concordance rate) was only slightly lower. This strongly suggests that body weight, and therefore obesity, is heavily influenced by genes.
• Yang et al. (2012) found that an increase in signalling in POMC neurons was positively correlated to age-dependent obesity in mice, suggesting neural factors may be able to explain why obesity increases with age.
• Bryant et al. (2008) report that disinhibited eaters have lower self-esteem, low physical activity and poorer psychological health and also experience lower success at dieting and incur greater weight regain, suggesting that disinhibition is strongly linked to vulnerability to obesity.
• Bartlett (2003) found dieting success occurs best with a target of reducing calorific intake of between 500 and 1,000 calories a day, resulting in weight loss of about 1—2 pounds a week, supporting the idea that achievable goal setting is a strong motivational force.
• Jeffery (2000) found obese people start regaining weight after 6 months due to failing to maintain behavioural changes, suggesting factors such as loss of motivation and social pressure have negative influences.
Evolutionary theory offers support for the genetic explanation, as it sees obesity as occurring through a tendency to overeat when food is available and store excess energy as fat for times of food scarcity, something that rarely occurs in the modern world of ever-available food. Such a tendency would be genetically transmitted.
Disinhibition is a major factor in weight gain leading to obesity, because of the high daily number of eating opportunities to be found in Western cultures.
Research suggests that social support is an important factor in dieting success. Organisations like Weight Watchers see their effectiveness as heavily due to the social support members offer to each other.
Genes cannot explain the upsurge in obesity. Genes have not changed, but environmental factors like the availability of food have, which lowers the validity of the genetic explanation.
Research into dieting is gender biased, as most research has centred on females and so cannot be generalised to males, who may have different reasons for dieting and be affected by different factors.
Ogden (2009) reviewed research into restraint theory and concluded that as restraint is detrimental to the physical and psychological health of normal weight individuals, it should not be used by overweight individuals vulnerable to becoming obese.
Research into explanations for obesity have helped form effective weight-reduction programmes, with the central factor being to achieve weight loss gradually over time and then to stabilise weight around an ideal target weight.