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

Objective
To make recommendations about preventing obesity in adults (18 to 65 y) in Canada.

Burden of Suffering
In a cross-sectional study conducted between 1986-1990 in Canadians aged 18-74, the prevalence of obesity (BMI ³ 27 kg/m²) was 35% in men and 27% in women. Three percent of men and 5% of women were found to be morbidly obese (BMI ³ 35 kg/m²). 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. Obesity has been causally linked to several diseases including coronary artery disease, hypertension, hyperlipidemia and diabetes. 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.

Options
Main preventive strategies were counselling and routine measurement of body mass index (BMI) (weight/height²). Other preventive and treatment strategies were community-based educational programs, dietary therapy (calorie-restricted diets), appetite suppressant drug therapy, behaviour therapy, surgery (vertical band gastroplasty, intragastric balloon insertion) and exercise.

Outcomes
Weight loss, recidivism.

Evidence
MEDLINE was searched for the years 1966 to June 1993 using the keywords obesity and weight reduction. Other data sources included bibliographies of review articles and recently published articles. Study results were synthesized in table or graphic format only.

Values
The 13-member Task Force of experts in family medicine, geriatric medicine, pediatrics, psychiatry and epidemiology used an evidence-based method for evaluating the effectiveness of preventive health care interventions. Recommendations were not based on cost-effectiveness of options. Patient preferences were not discussed.

Background papers providing critical appraisal of the evidence and tentative recommendations prepared by the chapter author were pre-circulated to the members. Evidence for this topic was presented and deliberated upon in 1- to 2-day meetings, 2 to 3 times per year from January 1993 to June 1993. Consensus was reached on final recommendations.

Benefits, Harms, and Costs
BMI is a reliable, easy measure, and correlates well with body fat content.

Evidence from RCTs and prospective cohort studies suggests that weight reduction in obese persons can lead to improvements in existing conditions such as diabetes, hypertension, hyperlipidemia and obstructive sleep apnea. Little evidence exists that treatment of obesity will prevent myocardial infarction, stroke or diabetes, or reduce mortality (p578).

2 large community-based cohort studies examined the effects of educational programs on weight loss. No significant differences in average weight loss were found 5 to 10 years post-intervention for communities who received and did not receive education.

Randomized controlled trials and cohort studies report that low calorie diets (1000 to 1500 kcal/day) and very low calorie diets (<800 kcal/day) result in weight reductions in the short-term. However, most patients returned to their pre-treatment weight within 1 to 5 years (576). Similar results were reported for appetite-suppressant drug therapy as an adjunct to dietary therapy. Behavioural therapy can result in modest weight losses (i.e., 0.5 to 0.75 kg/week), but again most losses are not sustained over the long term (p577). Lumen-reducing surgical procedures are usually considered only for persons with morbid obesity who have not responded to more conservative treatment. A small cohort study examining vertical band gastroplasty reported reduced mortality for selected patients. A placebo-controlled study found no significant difference in weight loss for patients treated with intragastric balloon inflation and those treated with dietary therapy (p577). There is little evidence that exercise combined with dietary and behavioural strategies augments weight loss unless there is a significant change in baseline exercise capacity.

Potential adverse effects vary by treatment. Diets of <1000 kcal can cause orthostatic hypotension, fatigue, hair loss, menstrual irregularities and symptomatic cholelithiasis. Adverse effects of drug therapy include drowsiness, fatigue and gastrointestinal discomfort. Surgical interventions can result in gastric ulceration, perforation and bowel obstruction. Observational studies suggest that weight reductions and fluctuations may lead to increased mortality and cardiovascular morbidity.

Recommendations
Recommendation grade [A, B, C, D, E]  and level of evidence [I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations in support of individual recommendations are identified in the guideline text.

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

• Insufficient evidence exists to recommend for or against counselling (during the PHE) to prevent obesity in adults [C, II-2].
• Insufficient evidence exists to include or exclude (from the PHE) routine measurement of height and weight, BMI or treatment of obesity [C, I, II-2]. Weight reduction may be "cautiously recommended" for persons with coexisting diabetes, hypertension or hyperlipidemia. For persons who are obese or in the upper-normal BMI range who are not candidates for weight reduction, or who have been unsuccessful at weight reduction, maintenance of a stable weight is a reasonable alternative.

Sponsors
The Canadian Task Force on Preventive Health Care developed this guideline with funding from Health Canada.

Source Document
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.