Canadian Guidelines for Body Weight Classification in Adults

1. Introduction

Highlights

• Body weight and concerns about body weight result in considerable physical, psychosocial, and economic costs in the Canadian population.
• Overweight and obesity have increased among Canadians over the past two decades and are linked to many common chronic diseases.
• Underweight, although much less prevalent, has significant health consequences.
• A body weight classification system can be used to identify weight-related health risks in populations and in individuals.
• The updated Canadian body weight classification system uses two measures to indicate health risks: the body mass index (BMI) and the waist circumference (WC).
• Both the 1988 "Canadian Guidelines for Healthy Weights" and the weight classification system of the World Health Organization form the basis of the 2003 "Canadian Guidelines for Body Weight Classification in Adults".

This technical report includes a description of a body weight classification system for adults age 18 years and older, including its uses and limitations. The report also includes a description of the technical information underlying the development of the system and recommendations for the future.

The concept of weight classification has a broader meaning than solely body weight. The body mass index (BMI) includes both height and weight and is significantly correlated with total body fat. It is an indicator of health risk associated with underweight, overweight and obesity. The waist circumference (WC) is positively correlated with abdominal fat and is an independent indicator of health risk associated with abdominal obesity.

This report is intended for researchers, health professionals and educators involved in the promotion of healthy weights and the treatment of weight-related health problems. A 'quick reference' resource for professionals on the body weight classification system has been developed to accompany this technical report (available online at: www.healthcanada.ca/nutrition). This report and the weight classification system described provide but one component of a comprehensive initiative needed to promote healthy weights in the Canadian population.

Although the weight classification system described in this report is for the adult population, a weight classification system for children and youth is also needed.

1.1 Weight-related health risks

The prevalence of overweight and obesity in Canadian adults has increased over the past two decades [1-3]. Overweight is associated with an increased risk for health problems such as type 2 diabetes, dyslipidemia, hypertension, coronary heart disease, gallbladder disease, obstructive sleep apnea, and certain cancers [4]. Table 1 provides a more comprehensive list of health problems that are associated with overweight and obesity.

Table 1 - Health problems associated with overweight and obesity

• Type 2 diabetes
• Dyslipidemia
• Insulin resistance
• Gallbladder disease
• Obstructive sleep apnea and respiratory problems
• Cardiovascular disease (e.g. coronary heart disease and ischemic stroke)
• Hypertension
• Osteoarthritis
• Some types of cancer (breast, endometrial, colon, prostate and kidney)
• Psychosocial problems
• Functional limitations
• Impaired fertility

The prevalence of underweight in Canada is small in comparison to the prevalence of overweight and obesity, however, the risks associated with underweight are significant [5-7]. This is evident in seniors where underweight is associated with conditions such as osteoporosis and respiratory disease and where underweight and/or weight loss may be early signs of underlying disease [8,9]. It is also evident in the small proportion of the population with eating disorders [10]. Table 2 provides a list of health problems associated with underweight.

Table 2 - Health problems associated with underweight*

• Undernutrition
• Osteoporosis
• Infertility
• Impaired immunocompetence

* Underweight may be an indication of an eating disorder or other underlying illness.

Finally, unhealthy practices such as smoking and restricted food habits used to manage body weight continue to be problems among segments of the population [11]. In addition, unhealthy attitudes toward weight, including dissatisfaction with weight and preoccupation with losing weight, even in the normal weight range, are common among young women [12]. There are also considerable economic costs associated with body weight problems in Canada [13].

1.2 Developing a body weight classification system

In general, a body weight classification system is based on information gathered from descriptive studies of large populations in which a range of body weights is correlated with health risk. Although health risks occur along a continuum of body weights, cut-off points along this continuum are made that define specific ranges of risk.

A weight classification system is based on populations that consist of diverse groups of individuals from different life-stages and different ethnic or racial backgrounds. In addition, a variety of weight-related health problems are analyzed in the development of a risk-based weight classification system. Health risks along the continuum may vary depending on these factors, which must be balanced in the development of a population-wide weight classification system. With regard to individuals, risk and protective factors that result, for example, from eating habits, physical activity patterns, tobacco use, and genetic influences may affect the risk of developing health problems, independent of weight status. Despite these limitations, a population-based weight classification system provides a useful tool for establishing health risks associated with body weight in the population and for conducting initial assessments to identify health risks in individuals.

The updated weight classification system for adults described in this report has evolved from previous work by Canadian researchers undertaken during the 1980's which culminated in the 1988 document, Canadian Guidelines for Healthy Weights. The 1988 document described the first body weight classification system accepted nationally for use by professionals, policy-makers, and the general public [5].

Further international studies led to the development of a global weight classification system by the World Health Organization (WHO) in 1995 [14], and the refinement of this system in 2000 [4]. The WHO has recommended that this system be adopted internationally [4]. Based, in part, on these recent developments by the WHO, a process was undertaken by Health Canada to review and update the 1988 Canadian Guidelines for Healthy Weights.

The updating process was undertaken through the combined efforts of Health Canada staff and an Expert Working Group that represented a wide range of disciplines related to body weight and health. A summary of the process followed to complete the update is provided in Appendix 7.1. Members of the Expert Working Group as well as the Health Canada project team are listed in Appendices 7.2 and 7.3. Appendix 7.4 lists background materials that were developed to support the update of the body weight classification system and Appendix 7.5 lists the key stakeholders that were consulted during an external consultation on the draft report.