life expectancy and survival throughout mankind s history was and remains dependent upon ability to cope with harmful stimuli . the human body itself developed very sophisticated defense mechanisms , which , however , are primarily based on rather primitive responses like inflammation , neurohormonal , and sympathetic nervous system activation . vital for all processes is energy , which is derived from fat , proteins , and carbohydrates . energetic efficacy of life organisms , although highest known in nature , is about 30% while the rest is lost primarily through heat production . chronic food shortage and malnutrition have been the scourge of humankind throughout history . this has led to development of safety measures to accumulate energy when available to bridge over times of need . as a matter of fact , an evolutionarily conserved gene family important for fat depots , which store twice the amount of energy as carbohydrates or proteins , until about a century or two ago , this gene family served its purposes for the majority of the world s population . nowadays , when abundant food is available all over the year , activation may be prolonged to lead to significant increase of body weight . it is therefore not surprising that attitudes of humankind towards body size changed throughout centuries . until recently , large body size reflected wealth and wellbeing , and it was reserved for very few in the community or population . nowadays , the other extreme is preferred and people are willing to deliberately reshape their body primarily due to aesthetic impulses , and less often due to health concerns . interesting in this context are differences between religions in their perception and presentation of goddesses : while thin stature was associated with lack and suffering , large body size with abundance and joy . similar observations stem from arts , literature , and medical opinion of the times , when corpulence meant something good and desirable . obesity in lay public is usually associated with large body size . for clinical practice and research purposes , the quetelet index is the ratio between body weight in kg and square of body height in meters . it was first described by the belgian polymath adolphe quetelet during the course of developing  social physics  , which would likely correspond to current understanding of epidemiology . the current name , body mass index ( bmi ) , dates to 1972 , when it was used as an estimation of body fat . thereafter , it was adopted for use in daily practice and also by the world health organization . according to its current definition , people with bmi < 18.5  kg / m are considered underweight while those with bmi over 30 and 40  kg / m are obese and morbidly obese , respectively . these ranges are based on healthy populations and are valid only as statistical categories , a fact that is largely being ignored . only with sufficient and accessible food , together with modern way of life and little or no physical activity , obesity increased in prevalence to reach epidemic proportions . obesity is today considered as a chronic disease and is listed in the international classification of disease ( icd-9 : e66.9 ) . consequently , people are much more worried by weight gain than weight loss , and dieting is frequently used to obtain a  healthy weight  . epidemiological studies , however , have demonstrated that aging attenuates association between high bmi and increased risk of death . in contrast to common public beliefs and guidelines for primary preventive medicine , high bmi confers protective effects for patients with established chronic diseases . although this seemingly paradoxical message penetrates the public opinion only slowly , evidence is starting to accumulate . about a decade ago , the first publication using  obesity paradox  in the article title was published . a pubmed search of february 6th , 2012 identified 96 publications that have used the exact phrase in their title , and 138 used both words in any combination ( fig .  1 ) . most studies used bmi to evaluate body size in relation to all - cause mortality . the message derived from small- to large - scale studies is uniform and suggests that an optimal bmi with lowest risk of death is in the overweight or even obese category . table  1 summarizes some of the most important publications about the obesity paradox in chronic cardiovascular , pulmonary , and kidney disease as well as in intensive care patients [ 919 ] . in a recent study , the presence of an obesity paradox has been observed in patients with diabetes mellitus plus cardiovascular comorbidity . the latter study in particular provides evidence in contrast to common thinking and to current guideline recommendations . these recommendations are commonly based on mere translation from primary prevention data and may not be applicable in patient populations with established chronic diseases . we believe that an intellectual exercise recently performed for heart failure   is valid for many chronic diseases . rather than merely repeating it over a plethora of conditions , we should bring the current knowledge and experience to a next level . while the relevant clinical question of weight management in overweight and obese chronic disease patients remains unanswered , we certainly should tailor our management individually . generally , non - edematous and particularly non - voluntary weight loss should be recorded and managed aggressively . if overlooked or ignored , a vicious circle of body wasting and eventually cachexia may ensue . even obese patients are vulnerable for such scenario , which is yet another obesity paradox to be explored in the currently ongoing studies investigating co - morbidities aggravating heart failure ( sica - hf ) . in real life , nothing is coincidental and you always reach a pay - off stage . obesity - induced symptoms or syndromes like sleep - disordered breathing in heart failure [ 23 , 24 ] obviously drive the trade - off between weight loss and obesity paradox and are yet another example of balancing in clinical practice . and this is where the long forgotten and neglected art of medicine should be revived ; to help us balance between thin and obese , between health and disease and the other way around.fig . individual words or a phrase in titletable 1large - scale studies about obesity paradox in chronic diseasecondition and study / countryn ( % men)agemain findingheart failure  acute108,927 ( 49%)72    14  yearsinhospital mortality decreased from 5.0% to 2.2% per bmi quartiles the mortality or for obese , overweight , and underweight vs healthy weight was 0.74 ( 95% ci 0.680.81 ) , 0.83 ( 95% ci 0.760.90 ) , and 1.34 ( 95% ci 1.151.58 ) , respectively  ( adhere registry )  chronic7,767 ( 75%)64    11  yearshigher bmi associated with lower mortality risk : adjusted hr for all - cause death for obese or overweight vs healthy weight patients was 0.81 ( 95% ci 0.720.92 ) and 0.88 ( 95% ci 0.800.96 ) , respectively  ( usa ) coronary artery disease  coronary artery disease and hypertension22,576 ( na)66    10  yearswith normal weight subjects as reference , overweight and obese patients had better ( hr 0.520.66 , p  <  0.001 ) and thin patients had worse survival ( hr 1.85 , p  <  0.001 )  ( invest ) percutaneous coronary intervention4,880 ( 70%)median age 62  yearspatients with bmi 27.530 kg / m had lowest adjusted hr for death ( 0.59 , 95% ci 0.390.90 )  ( germany )  coronary artery bypass grafting22,599 ( 72%)63    10  yearslowest rr for 30-day mortality in patients with bmi of 33  kg / m , patients with bmi  <  22 kg / m had significantly higher rr for death  ( germany ) stroke2,785 ( 62%)mean age 70  yearsobese and overweight patients had significantly higher early ( 1  week and 1  month ) and long - term ( 10  years ) survival when compared to patients with normal bmi ( p  <  0.001 for all)(greece ) intensive care unit9,935 ( 64%)63    15  yearsoverweight ( hr 0.86 , 95% ci 0.740.99 ) and obese ( hr 0.83 , 95% ci 0.690.99 ) patients had lower 60-day inhospital mortality.(germany ) chronic obstructive pulmonary disease  acute exacerbation968 ( 72%)70    9  yearsin an adjusted model , bmi per 1  kg / m unit increase was associated with 5% less chance of death ( hazard ratio 0.95 , 95% confidence interval 0.930.97 )  ( slovenia )  stable disease2,132 ( 57%)56    11  yearsadjusted rr for death in underweight vs normal weight patients was 1.64 ( 95% ci 1.202.23 ) in men and 1.42 ( 95% ci 1.071.89 ) in women  ( copenhagen city heart study ) chronic kidney disease121,762 ( 54%)63    15  yearshigher bmi ( optimal range 4045 ) was independently associated with better survival after adjustment for available surrogates of nutritional status and inflammation(davita dialysis facilities , usa ) diabetes plus cardiovascular disease5,202 ( 66)62    7  yearshigher bmi ( optimum range 3035  kg / m ) was associated with lower mortality and hospitalization . weight loss but not weight gain was predictive of increased mortality.proactive study bmi body mass index , or odds ratio , hr hazard ratio ; rr relative risk ; 95% ci 95% confidence interval pubmed search for publications with  obesity paradox individual words or a phrase in title large - scale studies about obesity paradox in chronic disease bmi body mass index , or odds ratio , hr hazard ratio ; rr relative risk ; 95% ci 95% confidence interval bmi is an easily accessible parameter that carries important information for patient risk stratification , and the so - called obesity paradox relates to beneficial effects of large body size in terms of mortality . the risks and benefits of overweight or obese bmi categories in healthy individuals and chronic disease patients , however , is diametrically different , and , thus , public and also medical healthcare providers perception has to be modified accordingly .
body size , particularly large , is a matter of concern among the lay public . whether this is justified depends upon the state of health and should be judged individually . for patients with established chronic disease 
 , there is sufficient evidence to support the benefits of large body size , i.e. , the obesity paradox . 
 this uniform finding is shared over a variety of cardiovascular , pulmonary , and renal diseases and is counterintuitive to the current concepts on ideal body weight . 
 the scientific community has to increase the awareness about differences for optimal body size in health and disease . 
 simultaneously , clinicians have to be aware about body weight dynamics implications and should interpret the changes in the context of an underlying disease in order to implement the best available management .