Full Text Review
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.
Prevention of Obesity in Adults
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
These recommendations were finalized by the Task Force in January 1994
Contents
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:
-
To develop a better understanding of the etiology and
pathophysiology of obesity, and to clarify the clinical importance of central
(android) obesity.
-
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.
-
To develop effective obesity prevention strategies.
-
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.
Evidence
The literature was identified with a MEDLINE search
for the years 1966
to June 1993
using the following key words: Obesity, weight reduction. Further references
were obtained from the bibliographies of review articles and recently published
articles that had not yet appeared in the MEDLINE directory. This review
was initiated in March 1993
and the recommendations were finalized by the Task Force in January 1994.
Full Citation
Link to Structured Abstract of
this review
Link to Summary Table of this
review
Link to Selected References list of this review
Link to 1999 update: Detection,
prevention and treatment of obesity
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