Please note: In 2003, the CTF updated its Grades of Recommendations to include an "I Recommendation" for situations where insufficient evidence exists to allow a recommendation to be made.  (Formerly, these situations were captured under a "C Recommendation".)  This change is not retroactive, and all "C Recommendations" made prior to 2003 have not been reevaluated in light of the new "I" recommendation grade.  For a discussion of these recommendation grades, please link to the 2003 article in the Canadian Medical Association Journal here.

Prepared by James Douketis, MD, Clinical Research Fellow in Thromboembolism, Department of Medicine, McMaster University and William Feldman, MD, FRCPC, Professor of Pediatrics and of Preventive Medicine and Biostatistics, University of Toronto, Ontario

Overview
The Canadian Guidelines for Healthy Weights and the Report of the Task Force on the Treatment of Obesity were published in 1988 and 1990 respectively. Both reports recognized that persons with a body mass index (BMI) of ³27 kg/m , who were considered obese, were at increased risk of health problems.< 1,2> The rationale for detecting the presence or absence of obesity is twofold: 1) To prevent the development of obesity in those with a normal BMI; and 2) To reduce weight in persons with obesity. It is hoped that detecting and treating obesity will decrease the incidence of coronary artery disease, diabetes, hypertension, hyperlipidemia and other diseases which have been linked to obesity. This, in turn, would reduce morbidity attributable to these diseases and lower overall mortality. This improvement in health status is predicated on sustained weight loss. At present there is insufficient evidence that these goals can be achieved based on the following conclusions: 1) Obesity prevention programs are ineffective in reducing the incidence of obesity; 2) Weight reduction is associated with a high rate of recidivism over the long term in the vast majority of persons, regardless of the weight loss method used; and 3) In obese persons there is no evidence that weight reduction will be longstanding and will translate into a reduction of morbidity (ie. reduced incidence of myocardial infarct, stroke, etc.) or lower mortality. However, one cannot exclude the possibility that weight reduction can have health benefits in a small minority of persons in whom long-term weight loss is successful. As well, in obese persons with coexistent diabetes, hypertension or hyperlipidemia, weight reduction can be recommended cautiously since this may improve the symptoms and management of these diseases. Obesity in children is discussed in a separate chapter (Chapter 30).

Burden of Suffering
In a cross-sectional study conducted between 1986-1990 in Canadians aged 18-74, the prevalence of obesity (BMI ³27 kg/m ) was 35% in men and 27% in women.<3> Three percent of men and 5% of women were found to be morbidly obese (BMI ³35 kg/m ). Factors associated with an increased prevalence of obesity include increased age, a low level of education, low physical activity, alcohol use in men and parity in women.<4> Obesity has been causally linked to several diseases including coronary artery disease, hypertension, hyperlipidemia and diabetes. The evidence supporting an independent association between obesity and these diseases is based on cross-sectional and longitudinal population-based cohort studies. These studies showed an increased prevalence of these diseases amongst obese persons as compared to non-obese persons, after controlling for potential confounding factors such as smoking and family history.<5-13> Recent data from several studies have suggested that the central form of obesity, as defined by an increased waist/hip ratio, correlates with the presence of the aforementioned diseases independent of the BMI.<11,12,14-18> Obesity has also been associated with other diseases including obstructive sleep apnea, cholelithiasis, venous thromboembolism, and certain neoplasms (breast, colon, endometrial, ovarian and prostate) although the evidence linking obesity to these conditions is not as extensive.<19> The psychological impact of obesity, although not as well studied, may be substantial, given the emphasis on a lean body image and the negative perception of an overweight state that currently exist in our society.

Obesity has also been independently associated with an increased mortality rate based on large prospective cohort studies.<5,7,19-21> These studies were of long duration, ranging from 10-26 years, were controlled for smoking behaviour, and eliminated early deaths during the follow-up period that may have been related to pre-existent sub-clinical disease unrelated to coexistent obesity.

Maneuver
The diagnosis of an obese state can be made using several methods (e.g. weight-height ratios, body circumference ratios, and skinfold thickness measurements). In Canada, the body mass index (BMI = weight/height) is the most widely accepted method of detecting the presence of obesity. This index is closely correlated with weight but largely independent of height. The BMI uses a statistical correction for height so that body weight will correlate maximally with adiposity. The BMI measurement is easily performed, reliable, and correlates well with body fat content.<22> In Canada, obesity is defined for both men and women as a BMI ³27 kg/m. A BMI above this cut-off is associated with an increased health risk. Morbid obesity is defined as a BMI in men or women ³35 kg/m.<1>

Effectiveness of Prevention and Treatment
At least two large community-based studies have assessed the effectiveness of educational programs aimed at encouraging weight reduction as part of an overall healthy lifestyle.<23,24> After five to ten years of intervention there was no significant difference in the average weight loss in the communities which received education as compared to control communities. Other educational interventions aimed at reducing cardiovascular risk factor prevalence have met with similarly disappointing results. (see Chapters 43 and 54)

The clinical approach to the management of obesity can be similar to the management of other chronic disorders such as diabetes, hyperlipidemia or most forms of hypertension. Lifelong dietary therapy and possibly long-term pharmacologic or behavioural treatment would be required to control obesity successfully. Given the high rate of recidivism following weight reduction, weight reduction targets should be realistic and modest weight loss or maintenance of a steady body weight may be appropriate therapeutic goals. The treatment of obesity should be individualized depending on each patient’s age, BMI, and the coexistence of other diseases such as diabetes, hypertension or hyperlipidemia which have been linked to obesity.

Dietary Therapy
Two types of calorie restricted diets are currently used. Low calorie diets (LCD) provide 1,000-1,500 kcal of energy daily. Very low calorie diets (VLCD) provide <800 kcal per day and require physician supervision. Numerous cohort studies and randomized trials have demonstrated effective weight reduction over the short term but few randomized trials have assessed the effectiveness of weight reduction over a 3-5 year period. For both LCDs and VLCDs approximately 50-78% of participants who lost weight initially returned to their baseline weight within 1-3 years.<25,26> In studies with a longer follow-up of up to five years a similar pattern has occurred, with the vast majority of persons who lost weight eventually returning to their original pre-treatment weight.<27,28> Sustained weight loss may be achieved in a small number of persons.

Appetite-suppressant Drug Therapy
There have been many recent placebo-controlled clinical trials of various appetite-suppressant drugs as adjuncts to dietary therapy in the treatment of obesity. Drug therapies have been shown to be effective in reducing weight when combined with a diet but the effects have been limited to periods when the drug is taken or when a predetermined diet is maintained. In general, as with dietary restriction, drug therapy may be effective in the short-term but long-term (i.e. 3-5 year) benefits have not been demonstrated except in a small minority of persons.<29-31>

Behavioural Therapy
Behavioral therapy when used alone for the treatment of obesity will lead to only modest weight loss (i.e. 0.5-0.75 kg/week). Consequently, this form of treatment is usually used in concert with other weight reduction methods. It has been postulated that long-term behavioural therapy may reinforce the necessary lifestyle and cognitive changes required to maintain long-term weight loss. However, even in studies with long-term weight loss counselling, sustained weight loss has been difficult to achieve in all but a few subjects.<32,33>

Surgical Therapy
Surgical therapy for obesity is usually considered only for persons with morbid obesity in whom more conservative forms of treatment have been unsuccessful although it is combined with dietary, and often with behavioural therapy. Vertical band gastroplasty is currently considered to be the most effective and safest of all gastric lumen reducing procedures. A small cohort study has reported improved mortality benefit in selected patients.<34> The use of intragastric balloon insertion has been compared with dietary therapy in a placebo-controlled study; weight loss was not found to be significantly different in either group.<35,36>

Exercise and the Treatment of Obesity
When combined with dietary and behavioural weight reduction methods, there is little evidence that exercise augments weight loss unless there is significant change in the baseline exercise capacity.<37,38> Exercise has been recommended as an adjunct to any weight reduction program since it may help people maintain their diet through a sense of psychological well-being, and this in turn may prevent weight regain. However, the Task Force recommends the regular practice of moderate to intense physical activity for the maintenance of a healthy body weight (Chapter 47).

Benefits of Weight Reduction
There is substantial evidence that treatment of obesity can improve the management of many of the purported sequelae of obesity. Based on randomized trials and prospective cohort studies, weight reduction has been shown to reduce systolic and diastolic blood pressures amongst obese persons with hypertension, independent of sodium intake, thereby reducing their antihypertensive drug requirements.<39,40> In obese diabetics, weight loss can improve glycemic control and reduce the need for or the dosage of oral hypoglycemics or insulin.<41> As well, weight loss can improve hyperlipidemic states and may significantly reduce symptoms in patients with obstructive sleep apnea.<42,43> The evidence that treating obesity will prevent major outcome events such as myocardial infarction, stroke or diabetes and will reduce mortality is sparse. This evidence is based on insurance company mortality data, retrospective analyses of prospective cohort studies and one retrospective study.<5,44,45> However, since weight reduction is usually short-lived this may attenuate or obscure any potential benefit that weight loss might achieve in terms of reduced major morbidity or mortality.

Risks Associated With the Treatment of Obesity
Weight reduction has been associated with several possible adverse effects, depending on the method of treatment. Diets of less than 1,000 kcal can cause orthostatic hypotension, fatigue, hair loss, transient menstrual irregularities and symptomatic cholelithiasis. Drug therapy can commonly cause drowsiness, fatigue and gastrointestinal discomfort. Gastroplasty and balloon insertion surgery can lead to gastric ulceration, perforation and bowel obstruction. Over the long term, weight reduction and fluctuations in weight (weight cycling) have been associated with increased cardiovascular morbidity and higher mortality.<46-48> These interesting results are based on observational studies that have certain methodologic limitations. Further prospective studies are required to address this important issue before definitive conclusions are made.

Recommendations of Others
In 1990 the Canadian Task Force on the Treatment of Obesity encouraged weight loss in obese persons with "coexistent health problems that can be ameliorated with weight loss and/or at risk of developing conditions associated with obesity (e.g., those with a family history of diabetes)". They advised weight loss in the presence of "upper body obesity" when the individual’s BMI was ³25 kg/m.<2> The U.S. National Institute of Health Technology Assessment Conference on obesity recommended treatment in persons with health problems that could be lessened by weight loss such as sleep apnea, hypertension or non-insulin-dependent diabetes mellitus, and that weight control might be appropriate in persons near the upper limit of the healthy weight range. The U.S. Preventive Services Task Force recommendation is currently under review.

Conclusions and Recommendations

*Note: These recommendations have been updated.
Link to recommendation table for 1999 update: Detection, prevention and treatment of obesity

There is insufficient evidence at this time to recommend the inclusion or exclusion in a routine physical examination of BMI measurement for persons aged 18-65, given the lack of long-term effectiveness of weight reduction therapy in the large majority of obese persons. Weight reduction can be cautiously recommended in obese persons with coexistent diseases who may benefit from weight loss, after taking into account the high recidivism rate and adverse effects of weight loss. For all persons, who are either obese or in the upper normal BMI range and in whom weight reduction is not indicated or has been unsuccessful, maintenance of a stable weight would be a reasonable alternative.<25> Moderate intensity physical activity, taking into account current fitness levels, is also recommended for all Canadians to maintain a healthy body weight (Chapter 47).

Unanswered Questions (Research Agenda)
The following are research priorities:

1. To develop a better understanding of the etiology and pathophysiology of obesity, and to clarify the clinical importance of central (android) obesity.
2. To design and execute long-term randomized trials or methodologically sound cohort studies so as to determine the effects of sustained weight reduction and weight cycling on well defined morbidity events and on mortality.
3. To develop effective obesity prevention strategies.
4. To develop effective weight reduction strategies in obese persons with coexistent diseases whose management may be improved by weight loss, and in other persons with obesity.

Full Citation
Douketis J. and Feldman W. Prevention of obesity in adults. In: Canadian Task Force on the Periodic Health Examination. Canadian Guide to Clinical Preventive Health Care. Ottawa: Health Canada, 1994; 574-84.