Unsolved:Obesity paradox

From HandWiki
Short description: Medical hypothesis

The obesity paradox is the finding in some studies of a lower mortality rate for overweight or obese people within certain subpopulations.[1][2][3] The paradox has been observed in people with cardiovascular disease and cancer. Explanations for the paradox range from excess weight being protective to the statistical association being caused by methodological flaws such as confounding, detection bias, reverse causality, or selection bias.[1]

Description

The terminology "reverse epidemiology" was first proposed by Kamyar Kalantar-Zadeh in the journal Kidney International in 2003[4] and in the Journal of the American College of Cardiology in 2004.[5] It is[clarification needed] a contradiction to prevailing medical concepts of prevention of atherosclerosis and cardiovascular disease; however, active prophylactic treatment of heart disease in otherwise healthy, asymptomatic people has been and is controversial in the medical community for several years.[6][7][clarification needed]

The mechanism responsible for this reversed association is unknown, but it has been theorized that, in chronic kidney disease patients, "The common occurrence of persistent inflammation and protein energy wasting in advanced CKD [chronic kidney disease] seems to a large extent to account for this paradoxical association between traditional risk factors and CV [cardiovascular] outcomes in this patient population."[8] Other research has proposed that the paradox also may be explained by adipose tissue storing lipophilic chemicals that would otherwise be toxic to the body.[9]

The obesity paradox (excluding the cholesterol paradox) was first described in 1999 in overweight and obese people undergoing hemodialysis,[10] and has subsequently been found in those with heart failure,[5][11][12] myocardial infarction,[13] acute coronary syndrome,[14] chronic obstructive pulmonary disease (COPD),[15] pulmonary embolisms,[16] and in older nursing home residents.[17]

While obese people have twice the risk of developing heart failure compared to individuals with a normal BMI,[18] once a person experiences heart failure, those with a BMI between 30.0 and 34.9 had lower mortality than those with a normal BMI. This has been attributed to the fact that people often lose weight when they have severe and chronic illness (a syndrome called cachexia).[19] Similar findings have been made in other types of heart disease. Among people with heart disease, those with class I obesity do not have greater rates of further heart problems than people of normal weight. In people with greater degrees of obesity, however, risk of further events is increased.[20][21] Even after cardiac bypass surgery, no increase in mortality is seen in the overweight and obese.[22][23] One study found that the improved survival could be explained by the more aggressive treatment obese people receive after a cardiac event.[24] Another found that if one takes into account COPD in those with peripheral artery disease, the benefit of obesity no longer exists.[25] The obesity paradox is also relevant in discussion of weight loss as a preventative health measure – weight-cycling (a repeated pattern of losing and then regaining weight) is more common in obese people, and has health effects commonly assumed to be caused by obesity, such as hypertension, insulin resistance, and cardiovascular diseases.[26]

Criticisms

Methodology

The obesity paradox has been criticized on the grounds of being an artifact arising from biases in observational studies. Strong confounding by smoking has been noted by several researchers,[27][28] although others have suggested that smoking does not account for the observed patterns.[29][30] Since smokers, who are subject to higher mortality rates, also tend to be leaner, inadequate adjustment for smoking would lead to underestimations of the risk ratios associated with the overweight and obese categories of BMI among non-smokers. In an analysis of 1.46 million individuals, restriction to never-smoking participants greatly reduced the mortality estimates in the underweight group, as well as strengthening the estimates in the overweight and obese groups.[31] This study concluded that, for non-Hispanic white adults who have never smoked, the BMI range of 20.0 to 24.9 was associated with the lowest mortality rates.[31] A similar 2016 study found that, of the BMI ranges studied (which ranged from 18.5 to >30), the "normal" 18.5–22.4 BMI range combined with healthy eating, high levels of physical activity, not smoking, and no more than moderate alcohol consumption was associated with the lowest risk of premature death.[32]

Another concern is reverse causation due to illness-induced weight loss. That is, it may not be low BMI that is causing death (and thereby making obesity seem protective) but rather imminent death causing low BMI. Indeed, unintentional weight loss is an extremely significant predictor of mortality.[33] Terminally ill individuals often undergo weight loss before death, and classifying those individuals as lean greatly inflates the mortality rate in the normal and underweight categories of BMI, while lowering the risk in the higher BMI categories. Studies that employ strategies to reduce reverse causation such as excluding sick individuals at baseline and introducing time lag to exclude deaths at the beginning of follow-up have yielded estimates of increased risk for body mass indices above 25 kg/m2.[34]

The obesity paradox may therefore result from people becoming lean due to smoking, sedentary lifestyles, and unhealthy diets – all factors which also negatively impact health.[32]

Critics of the paradox have also argued that studies supporting its existence almost always use BMI as the only measure of obesity.[citation needed] However, because BMI is an imperfect method of measuring obesity, critics argue that studies using other measures of obesity in addition to BMI, such as waist circumference and waist to hip ratio, render the existence of the paradox questionable.[35]

One probable methodological explanation for the obesity paradox in regards to cardiovascular disease is collider stratification bias, which commonly emerges when one restricts or stratifies on a factor (the "collider") that is caused by both the exposure (or its descendants) of an unmeasured variable and the outcome (or its ancestors / risk factors). In the example of the obesity-cardiovascular disease relationship, the obesity is the collider, the outcome is cardiovascular disease, and the unmeasured variables are environmental and genetic factors – given that obesity and cardiovascular disorders are often associated with each other, medical professionals may be reluctant to consider both other causes of cardiovascular disease or other causes of protection against said diseases.[36][37]

A study from 2018 found that the reason why overweight or obese patients supposedly live longer with cardiovascular disease than people of normal weight is simply because overweight / obese patients get cardiovascular disease at an earlier age, meaning while they survive more years with it, non-obese patients don't get cardiovascular disease at all up until later in life. In fact, the obese have shorter lifespans because they get cardiovascular disease at an early age and have to live a longer proportion of their life with it. This also shows a misunderstanding regarding the paradox: While survival rate once sick is indeed higher for those with obesity than for those few non-obese that have cardiovascular disease, people without obesity usually do not get cardiovascular disease in the first place.[38][39]

Ties to Coca-Cola

It has also been noted that Coca-Cola has promoted the hypothesis and funded researchers who agree with the hypothesis, which has raised questions about what research the company supports and why.[40]

Weight relativism

Dixon et al. have proposed that a paradox does not actually exist, as people can be healthy at a range of sizes. As one study puts it, "There is no 'obesity paradox' to explain, if we accept the premise that varying ideal weight ranges apply to individuals over different stages of the life span, accordingly allowing us to abandon the rigid biologically implausible concept of a single 'ideal weight' (for height) or weight range."[41]

See also

  • French paradox
  • Israeli paradox
  • Low birth-weight paradox (Low birth-weight babies born to smokers have a lower mortality than low birth-weight babies born to non-smokers, because other causes of low birth-weight are more harmful than smoking.)
  • Katherine Flegal
  • Social stigma of obesity

References

  1. ↑ 1.0 1.1 Lennon, Hannah; Sperrin, Matthew; Badrick, Ellena; Renehan, Andrew G. (2016). "The Obesity Paradox in Cancer: a Review" (in en). Current Oncology Reports 18 (9): 56. doi:10.1007/s11912-016-0539-4. ISSN 1523-3790. PMID 27475805. 
  2. ↑ Flegal, Katherine; Kit, Brian; Orpana, Heather (2 January 2013). "Association of All-Cause Mortality With Overweight and Obesity Using Standard Body Mass Index Categories". Journal of the American Medical Association 309 (1): 71–82. doi:10.1001/jama.2012.113905. PMID 23280227. 
  3. ↑ Carnethon, Mercedes; De Chaves, Peter John; Biggs, Mary (8 August 2012). "Association of Weight Status with Mortality in Adults with Incident Diabetes". Journal of the American Medical Association 308 (6): 581–90. doi:10.1001/jama.2012.9282. PMID 22871870. 
  4. ↑ Kalantar-Zadeh, Kamyar; Block, Gladys; Humphreys, Michael H.; Kopple, Joel D. (2003). "Reverse epidemiology of cardiovascular risk factors in maintenance dialysis patients". Kidney International 63 (3): 793–808. doi:10.1046/j.1523-1755.2003.00803.x. PMID 12631061. 
  5. ↑ 5.0 5.1 Kalantar-Zadeh, Kamyar; Block, Gladys; Horwich, Tamara; Fonarow, Gregg C (2004). "Reverse epidemiology of conventional cardiovascular risk factors in patients with chronic heart failure". Journal of the American College of Cardiology 43 (8): 1439–44. doi:10.1016/j.jacc.2003.11.039. PMID 15093881. https://escholarship.org/uc/item/3cs2f652. 
  6. ↑ Naghavi, Morteza; Falk, Erling; Hecht, Harvey S.; Shah, Prediman K.; Shape Task Force (2006). "The First SHAPE (Screening for Heart Attack Prevention and Education) Guideline". Critical Pathways in Cardiology 5 (4): 187–90. doi:10.1097/01.hpc.0000249784.29151.54. PMID 18340236. 
  7. ↑ Pearson, T. A. (2007). "The Prevention of Cardiovascular Disease: Have We Really Made Progress?". Health Affairs 26 (1): 49–60. doi:10.1377/hlthaff.26.1.49. PMID 17211013. 
  8. ↑ "Article: Vascular disease and chronic renal failure: new insights (abstract) - January 2010 - NJM". https://www.njmonline.nl/article.php?i=122&d=551&a=873. 
  9. ↑ Hong, N-S; Kim, K-S; Lee, I-K; Lind, P M; Lind, L; Jacobs, D R; Lee, D-H (27 September 2011). "The association between obesity and mortality in the elderly differs by serum concentrations of persistent organic pollutants: a possible explanation for the obesity paradox". International Journal of Obesity 36 (9): 1170–1175. doi:10.1038/ijo.2011.187. PMID 21946706. 
  10. ↑ Schmidt, Darren S.; Salahudeen, Abdulla K. (2007). "CARDIOVASCULAR AND SURVIVAL PARADOXES IN DIALYSIS PATIENTS: Obesity-Survival Paradox-Still a Controversy?". Seminars in Dialysis 20 (6): 486–92. doi:10.1111/j.1525-139X.2007.00349.x. PMID 17991192. 
  11. ↑ Sharma, A; Lavie, CJ; Borer, JS; Vallakati, A; Goel, S; Lopez-Jimenez, F; Arbab-Zadeh, A; Mukherjee, D et al. (15 May 2015). "Meta-analysis of the relation of body mass index to all-cause and cardiovascular mortality and hospitalization in patients with chronic heart failure.". The American Journal of Cardiology 115 (10): 1428–34. doi:10.1016/j.amjcard.2015.02.024. PMID 25772740. http://espace.library.uq.edu.au/view/UQ:355802/UQ355802_OA.pdf. 
  12. ↑ Padwal, R; McAlister, F A; McMurray, J J V; Cowie, M R; Rich, M; Pocock, S; Swedberg, K; Maggioni, A et al. (31 October 2013). "The obesity paradox in heart failure patients with preserved versus reduced ejection fraction: a meta-analysis of individual patient data". International Journal of Obesity 38 (8): 1110–1114. doi:10.1038/ijo.2013.203. PMID 24173404. 
  13. ↑ Wang, L; Liu, W; He, X; Chen, Y; Lu, J; Liu, K; Cao, K; Yin, P (4 September 2015). "Association of overweight and obesity with patient mortality after acute myocardial infarction: A meta-analysis of prospective studies". International Journal of Obesity 40 (2): 220–8. doi:10.1038/ijo.2015.176. PMID 26338077. 
  14. ↑ Niedziela, J; Hudzik, B; Niedziela, N; Gąsior, M; Gierlotka, M; Wasilewski, J; Myrda, K; Lekston, A et al. (November 2014). "The obesity paradox in acute coronary syndrome: a meta-analysis.". European Journal of Epidemiology 29 (11): 801–12. doi:10.1007/s10654-014-9961-9. PMID 25354991. 
  15. ↑ Cao, Chao; Wang, Ran; Wang, Jianmiao; Bunjhoo, Hansvin; Xu, Yongjian; Xiong, Weining; Simpson, Colin (24 August 2012). "Body Mass Index and Mortality in Chronic Obstructive Pulmonary Disease: A Meta-Analysis". PLOS ONE 7 (8): e43892. doi:10.1371/journal.pone.0043892. PMID 22937118. Bibcode: 2012PLoSO...743892C. 
  16. ↑ Stein, Paul; Matta, Fadi; Goldman, Jose (2011). "Obesity and pulmonary embolism: The mounting evidence of risk and the mortality paradox". Thrombosis Research 128 (6): 518–523. doi:10.1016/j.thromres.2011.10.019. PMID 22078437. https://www.sciencedirect.com/science/article/pii/S0049384811005597. Retrieved 2021-10-29. 
  17. ↑ Veronese, N; Cereda, E; Solmi, M; Fowler, SA; Manzato, E; Maggi, S; Manu, P; Abe, E et al. (November 2015). "Inverse relationship between body mass index and mortality in older nursing home residents: a meta-analysis of 19,538 elderly subjects.". Obesity Reviews 16 (11): 1001–15. doi:10.1111/obr.12309. PMID 26252230. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-121461. 
  18. ↑ Kenchaiah, Satish (Aug 1, 2002). "Obesity and the risk of heart failure". New England Journal of Medicine 347 (5): 305–13. doi:10.1056/NEJMoa020245. PMID 12151467. 
  19. ↑ Habbu, Amit; Lakkis, Nasser M.; Dokainish, Hisham (2006). "The Obesity Paradox: Fact or Fiction?". The American Journal of Cardiology 98 (7): 944–8. doi:10.1016/j.amjcard.2006.04.039. PMID 16996880. 
  20. ↑ Romero-Corral, Abel; Montori, Victor M; Somers, Virend K; Korinek, Josef; Thomas, Randal J; Allison, Thomas G; Mookadam, Farouk; Lopez-Jimenez, Francisco (2006). "Association of bodyweight with total mortality and with cardiovascular events in coronary artery disease: A systematic review of cohort studies". The Lancet 368 (9536): 666–78. doi:10.1016/S0140-6736(06)69251-9. PMID 16920472. 
  21. ↑ Oreopoulos, Antigone; Padwal, Raj; Kalantar-Zadeh, Kamyar; Fonarow, Gregg C.; Norris, Colleen M.; McAlister, Finlay A. (2008). "Body mass index and mortality in heart failure: A meta-analysis". American Heart Journal 156 (1): 13–22. doi:10.1016/j.ahj.2008.02.014. PMID 18585492. https://escholarship.org/uc/item/84z6x7fs. 
  22. ↑ Oreopoulos, Antigone; Padwal, Raj; Norris, Colleen M; Mullen, John C; Pretorius, Victor; Kalantar-Zadeh, Kamyar (2008). "Effect of Obesity on Short- and Long-term Mortality Postcoronary Revascularization: A Meta-analysis". Obesity 16 (2): 442–50. doi:10.1038/oby.2007.36. PMID 18239657. https://escholarship.org/uc/item/75m3g7z6. 
  23. ↑ Mariscalco, G; Wozniak, MJ; Dawson, AG; Serraino, GF; Porter, R; Nath, M; Klersy, C; Kumar, T et al. (28 February 2017). "Body Mass Index and Mortality Among Adults Undergoing Cardiac Surgery: A Nationwide Study With a Systematic Review and Meta-Analysis.". Circulation 135 (9): 850–863. doi:10.1161/CIRCULATIONAHA.116.022840. PMID 28034901. 
  24. ↑ Diercks, Deborah B.; Roe, Matthew T.; Mulgund, Jyotsna; Pollack, Charles V.; Kirk, J. Douglas; Gibler, W. Brian; Ohman, E. Magnus; Smith, Sidney C. et al. (2006). "The obesity paradox in non–ST-segment elevation acute coronary syndromes: Results from the Can Rapid risk stratification of Unstable angina patients Suppress ADverse outcomes with Early implementation of the American College of Cardiology/American Heart Association Guidelines Quality Improvement Initiative". American Heart Journal 152 (1): 140–8. doi:10.1016/j.ahj.2005.09.024. PMID 16824844. 
  25. ↑ "Obesity Paradox" in Chronic Obstructive Pulmonary Disease
  26. ↑ Bacon L, Aphramor L (2011). "Weight science: evaluating the evidence for a paradigm shift.". Nutrition Journal 10: 9. doi:10.1186/1475-2891-10-9. PMID 21261939. 
  27. ↑ Stokes, Andrew (2015). "Smoking and reverse causation create an obesity paradox in cardiovascular disease.". Obesity 23 (12): 2485–90. doi:10.1002/oby.21239. PMID 26421898. 
  28. ↑ Preston, Samuel; Stokes, Andrew (2014). "Obesity Paradox: Conditioning on Disease Enhances Biases in Estimating the Mortality Risks of Obesity.". Epidemiology 25 (3): 454–461. doi:10.1097/EDE.0000000000000075. PMID 24608666. 
  29. ↑ Glymour; Vittinghoff (2014). "Commentary: selection bias as an explanation for the obesity paradox: just because it's possible doesn't mean it's plausible.". Epidemiology 25 (1): 4–6. doi:10.1097/EDE.0000000000000013. PMID 24296924. 
  30. ↑ Flegal, Katherine M.; Graubard, Barry; Williamson, David; Gail, Mitchell (2007). "Impact of Smoking and Preexisting Illness on Estimates of the Fractions of Deaths Associated with Underweight, Overweight, and Obesity in the US Population". American Journal of Epidemiology 166 (8): 975–982. doi:10.1093/aje/kwm152. PMID 17670912. 
  31. ↑ 31.0 31.1 "Body-mass index and mortality among 1.46 million white adults". The New England Journal of Medicine 363 (23): 2211–9. 2010. doi:10.1056/NEJMoa1000367. PMID 21121834. 
  32. ↑ 32.0 32.1 Veronese, Nicola; Li, Yanping; Manson, JoAnn E; Willett, Walter C; Fontana, Luigi; Hu, Frank B. (2016) "Combined associations of body weight and lifestyle factors with all cause and cause specific mortality in men and women: prospective cohort study", BMJ, v355. doi: [1].
  33. ↑ Harrington, Mary; Gibson, Sigrid; Cottrell, Richard (2009). "A review and meta-analysis of the effect of weight loss on all-cause mortality risk.". Nutr Res Rev 22 (1): 93–108. doi:10.1017/S0954422409990035. PMID 19555520. 
  34. ↑ Prospective Studies Collaboration (2009). "Body-mass index and cause-specific mortality in 900 000 adults: collaborative analyses of 57 prospective studies". The Lancet 373 (9669): 1083–1096. doi:10.1016/S0140-6736(09)60318-4. PMID 19299006. 
  35. ↑ Chrysant, Steven G.; Chrysant, George S. (January 2013). "New insights into the true nature of the obesity paradox and the lower cardiovascular risk". Journal of the American Society of Hypertension 7 (1): 85–94. doi:10.1016/j.jash.2012.11.008. PMID 23321407. 
  36. ↑ J., Rothman, Kenneth (2008). Modern epidemiology. Greenland, Sander, 1951–, Lash, Timothy L. (3rd edition, thoroughly revised and updated ed.). Philadelphia. ISBN 9780781755641. OCLC 169455558. 
  37. ↑ Banack, Hailey R.; Kaufman, Jay S. (May 2014). "The obesity paradox: Understanding the effect of obesity on mortality among individuals with cardiovascular disease". Preventive Medicine 62: 96–102. doi:10.1016/j.ypmed.2014.02.003. ISSN 0091-7435. PMID 24525165. 
  38. ↑ Sadiya S. Kahn et al. (April 2018). "Association of Body Mass Index With Lifetime Risk of Cardiovascular Disease and Compression of Morbidity". JAMA Cardiology 3 (4): 280–287. doi:10.1001/jamacardio.2018.0022. PMID 29490333. 
  39. ↑ Karen Kaplan (February 28, 2018). "The obesity paradox debunked: People with extra pounds do not live longer, study shows". Los Angeles Times. https://www.latimes.com/science/sciencenow/la-sci-sn-obesity-paradox-debunked-20180228-story.html. 
  40. ↑ Julia Belluz (October 20, 2015). "The obesity paradox: Why Coke is promoting a theory that being fat won't hurt your health". Vox. https://www.vox.com/2015/10/20/9572295/coca-cola-obesity-paradox. 
  41. ↑ Dixon, J.B.; Egger, G.J.; Finkelstein, E.A.; Kral, J.G.; Lambert, G.W. (January 2015). "'Obesity paradox' misunderstands the biology of optimal weight throughout the life cycle". International Journal of Obesity 39 (1): 82–84. doi:10.1038/ijo.2014.59. PMID 24732145. 

Further reading



Retrieved from "https://handwiki.org/wiki/index.php?title=Unsolved:Obesity_paradox&oldid=3265745"