- Causation or Association?
- Possible explanations
- Implications for treatment and preventative strategies
Depression is a mental condition characterised by loss of pleasure in enjoyable activities, and states of pessimism and intense sadness. Depression is commonly measured through an individual’s response to surveys. Depressive symptoms are not measured over a period of time but reflect the individual’s feelings at that point in time, leading to an inefficiency in this method of measurement. Studies that use suicide to reflect depression are subject to bias due to the variety of conditions that may lead to suicide, such as obesity, gender or circumstance.
Obesity can be defined as an excess of body fat. It is commonly measured through the Body Mass Index (BMI), which compares a person’s weight and height. A BMI greater than 30kg/m2 indicates obesity, while a BMI between 25-30kg/m2 signals overweight. World obesity is increasing at an alarming rate, so much so that the phrase â€œobesity epidemicâ€ has become common. In Australia, the 1999-2000 Australian Diabetes Obesity and Lifestyle Study found that 60% of Australians over 25 years were overweight, and 21% of those were obese. Obesity leads to conditions such as heart disease, stroke and diabetes, resulting in a lower life expectancy.
Depression has been associated with obesity, but it has not yet been proven that one causes the other. In fact, it is incredibly difficult to do so because the relationship is complicated by other factors, such as socioeconomic class and genetic make up.
To determine if depression leads to obesity or vice versa, large population studies need to be carried out over a period of time. Northern Finland recently published results of a study that followed a 1966 birth cohort to assess the chance of obesity and depression in young adults (up to the age of 31 years). Results indicated that teenage obesity increases the chance of suffering depression as a young adult. Similarly, depression and obesity can occur at the same time in females in adulthood and adolescence. Abdominal obesity was found to be a strong predictor of depression.
Many explanations have been proposed to link obesity and depression, although no cause and effect has been proven.
Depression can result in dietary behaviours which may lead to obesity. Binge eating or comfort eating may result from depression, which is also associated with increased alcohol unhealthy food consumption.
Poor diets, particularly ones low in folic acid, are associated with depression. Social stigma associated with obesity may lead to depression later in life, especially in young women. This may be emphasised in social groups in which there are lower rates of obesity.
Medications used to treat depression can result in obesity. Tricyclic antidepressants (TCAs) may lead to excessive weight gain. However, serotonergic antidepressants do not lead to weight gain.
On the other hand, treatments for obesity such as gastric bypass surgery may improve an individual’s mood.
Recent research suggests that leptin may cause higher levels of depression amongst the obese. Leptin is a hormone derived from fat cells, and is thought to play a role in mood regulation and emotion. Leptin deficiency is a suggested cause of depression, but obesity is associated with very high levels of leptin.
Leptin leads to fat tissue loss when given to people of normal weight, but not in those who are obese. This indicates resistance to leptin in obese people – although levels of the hormone are high in their blood, their bodies do not react to it. Therefore, leptin becomes less effective in regulating mood, and obese people have a higher risk of depression.
Physical inactivity can cause both depression and obesity. Physical activity is associated with higher levels of psychological wellness, caused by increased levels of chemicals in the brain which elevate mood.
Sometimes the results of a study may be affected by confounding factors. In relation to the link between obesity and depression, these include socio-economic status, genetic make-up, gender, age and marital status. Most studies still found a link between obesity and depression even after adjusting for these factors.
Treatment and prevention strategies for obesity and depression could be improved if the exact relationship between them is found. Drugs could be used to treat depression and obesity at the same time, and interventions could look at targeting both obesity and depression. For example, nutrition programs could also stress the importance of being mentally healthy.
The most effective weight loss programs generally include behavioural therapies. These programs encourage changes in behaviour to help an individual maintain long term weight loss.
For example, meal replacement programs that include referrals to health professionals (e.g. dietitians and psychologists) will be more effective than other programs based solely on diet. For the morbidly obese, the benefits of surgery (e.g. gastric banding) may be aided by regular psychological assessment and therapy. Pharmacological treatment with Xenical or Reductil should also include regular support and counselling to ensure weight loss is maintained.
For more information on obesity, health and social issues, and methods of weight loss, as well as some useful tools, see Obesity and Weight Loss.
For more information on living with obesity, including discussing obesity with friends or loved ones, bullying and obesity in children, obesity and its cost on the workplace and links between obesity and pain, sexuality and fertility, see Living with Obesity.
- Herva A, Laitinen J et al. Obesity and depression:results from the logitudinal Northern Finland 1966 Birth Cohort Study International Journal of Obesity 2006 30:S20-S27
- “depression n.” A Dictionary of Psychology. Andrew M. Colman. Oxford University Press, 2006. Oxford Reference Online. Oxford University Press. University of Western Australia. 27 February 2008
- Bjerkeset O, Romundstad P et al. Association of Adult Body Mass Index and Height with Anxiety, Depression, and Suicide in the General Population The HUNT Study. American Journal of Epidemiology 2007; 167; 2: 193-202
- “obesity n.” Concise Medical Dictionary. Oxford University Press, 2007. Oxford Reference Online. Oxford University Press. University of Western Australia. 27 February 2008
- Australian Institute of Health and Welfare (AIHW) Overweight and Obesity [online]. 2004 [cited 2008 February 27]. Available from: URL: http://www.aihw.gov.au/riskfactors/overweight.cfm
- Stunkard AJ, Faith MS and Allison KC. Depression and Obesity. Biol Psychiatry 2003; 54: 330-337
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- Simon GE, Von Korff M et al. Association between obesity and psychiatric disorders in the US adult population. Arch Gen Psychiatry 2006 63:824-830
- Lu XY The leptin hypothesis of depression: a potential link between mood disorders and obesity? Current Opinion in Pharmacology 2007; 7:648-652
- NHMRC, Clinical Practice Guidelines for the Management of Overweight and Obesity in Adults, Commonwealth of Australia 2003. Available [online] at URL: http://www.health.gov.au/internet/wcms/Publishing.nsf/Content/obesityguidelines-guidelines-adults.htm/$FILE/adults.pdf
- Victorian Government (Australia), Cognitive Behaviour Therapy, Victorian Government Last Updated: June 2007. Available [online] at URL: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Cognitive_behaviour_therapy?open