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Obesity in adults: Health consequences

George A Bray, MD
Leigh Perreault, MD
Section Editor
F Xavier Pi-Sunyer, MD, MPH
Deputy Editor
Kathryn A Martin, MD


The mortality and morbidity associated with being overweight or obese have been known to the medical profession for more than 2000 years [1]. Overweight refers to a weight above the "normal" range. This is determined by calculating the body mass index (BMI, defined as the weight in kilograms divided by height in meters squared). Overweight is defined as a BMI of 25 to 29.9 kg/m2, obesity as a BMI of >30 kg/m2. Severe obesity is defined as a BMI >40 kg/m2 (or ≥35 kg/m2 in the presence of comorbidities).

Obesity in adulthood is associated with a striking reduction in life expectancy for both men and women. In fact, it has been suggested that the steady rise in life expectancy during the past two centuries may come to an end because of the increasing prevalence of obesity [2]. Individuals who are both obese and smoke have a substantially greater reduction in life expectancy than nonobese smokers or obese nonsmokers [3].

The health hazards associated with obesity are reviewed here. The prevalence of and therapy for obesity and the evaluation of the overweight patient are discussed elsewhere. (See "Obesity in adults: Overview of management" and "Obesity in adults: Prevalence, screening, and evaluation".)


Effect of BMI on mortality — In general, greater body mass index (BMI), calculated as weight (in kg) divided by height (in m2), is associated with increased rate of death from all causes and from cardiovascular disease (CVD) (figure 1). The risk profile can be expressed as a J-shaped curve with progressively greater mortality as BMI increases >25 kg/m2. This is particularly true for those with severe obesity [4].

Obesity — A number of large epidemiologic studies have evaluated the relationship between obesity and mortality [4-15]. In the largest meta-analysis to date of 230 cohort studies including over 30 million individuals, both obesity and overweight were associated with an increased risk of all-cause mortality [16]. The nadir of risk was observed at BMI 20 to 22 kg/m2 in studies of healthy, never-smokers with the longest duration of follow-up (≥20 years).


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Literature review current through: Nov 2016. | This topic last updated: Mon Dec 05 00:00:00 GMT+00:00 2016.
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