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Cat no: H49-179/2003E
Publications ID: 4645
This technical report describes a body weight classification system for Canadian adults, including the development, uses, interpretation and limitations of the system. The report was developed by Health Canada staff and an Expert Working Group of Canadian researchers and practitioners, and reviewed by leading Canadian organizations. It is intended for health professionals, researchers and educators involved in research and practice related to body weight.
The weight classification system can be used to identify weight-related health risks in populations and in individuals. It is intended for use among Canadian adults age 18 years and older. At the individual level, the system should be used as one part of a more comprehensive assessment of health risk.
The weight classification system provides a scheme for categorizing health risk according to body weight, as measured by body mass index (BMI), and level of abdominal fat, as measured by waist circumference (WC). BMI (kg/m2) is the most useful indicator, to date, of weight-related health risk, and WC is a practical indicator of risk associated with excess abdominal fat.
There is a continuous relationship between gradations of BMI and health risk, and between WC and health risk. However, cut-off points for each of these measures have been established for the purpose of identifying different levels of health risk. These cut-off points are not intended as targets for intervention purposes in individuals.
The following categories of BMI are used to identify levels of health risk (relative to 'normal weight' category) as follows:
Health risks associated with the underweight category include undernutrition, osteoporosis, infertility, and impaired immunocompetence. Underweight may also be an indication of an eating disorder or other underlying illness. Health risks associated with overweight and obesity include type 2 diabetes, dyslipidemia, hypertension, coronary heart disease, gallbladder disease, obstructive sleep apnea, and certain cancers.
Waist circumference is also an important indicator of health risk. Sex-specific cut-off points for WC have been established to identify health risk associated with excess abdominal fat.
For men: WC >= 102 cm (40 in.)
For women: WC >= 88 cm (35 in.)
A WC above these cut-off points is associated with increased risk (relative to a WC below these values) of type 2 diabetes, coronary heart disease, and hypertension. The WC measurement should be used among those with BMIs between 18.5 and 34.9, to identify additional risk. For BMIs >= 35.0, the WC measurement does not provide additional information on health risk.
The system is recommended for use among Canadian adults, except pregnant and lactating women. There are some limitations to the use of this weight classification system among certain groups. Special considerations are required when applying this system to:
The weight classification system described in this report is an update of the 1988 Canadian Guidelines for Healthy Weights. It is in accord with the weight classification system released by the World Health Organization, which has been widely adopted internationally.
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.
The prevalence of overweight and obesity in Canadian adults has increased over the past two decadesFootnote 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 cancersFootnote 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
The prevalence of underweight in Canada is small in comparison to the prevalence of overweight and obesity, however, the risks associated with underweight are significantFootnote 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 diseaseFootnote 8,Footnote 9. It is also evident in the small proportion of the population with eating disorders Footnote 10. Table 2 provides a list of health problems associated with underweight.
Table 2 - Health problems associated with underweight*
* 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 populationFootnote 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 womenFootnote 12. There are also considerable economic costs associated with body weight problems in CanadaFootnote 13.
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 publicFootnote 5.
Further international studies led to the development of a global weight classification system by the World Health Organization (WHO) in 1995Footnote 14, and the refinement of this system in 2000Footnote 4. The WHO has recommended that this system be adopted internationallyFootnote 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.
The Canadian Guidelines for Body Weight Classification in Adults provides a scheme for classifying body weight, as measured by the body mass index (BMI), according to the level of health risk. The BMI is an index of weight to height (kg/m2) and is considered to be the most useful indicator of health risks associated with both overweight and underweightFootnote 4,Footnote 14. Table 3 shows the level of health risk associated with the range of BMIs in each of the BMI categories. The BMI, however, does not provide an indication of the distribution of fat in the body and research has shown that excess fat in the abdominal area is associated with an increased risk to health.
The measurement of waist circumference (WC) provides a simple and practical method for estimating abdominal fat and is an independent indicator of health problems associated with abdominal obesityFootnote 4,Footnote 15. Table 4 shows the health risk associated with an elevated WC. Table 5 illustrates levels of risk associated with the BMI and WC combined.
The level of health risk refers to relative risk, that is, the risk of developing health problems in those with abnormal levels or distribution of body fat, as measured by BMI or WC, compared to those in a normal range. It is important to note that the risk for an individual will be influenced by a unique combination of factors which must be considered in addition to BMI and/or WCFootnote 16. It is also important to note that BMI does not reflect weight history. Recent weight gains or weight losses may be associated with health risks independent of BMI categorization and require assessment in individualsFootnote 14.
Tables 3, 4, and 5 provide a synopsis of the body weight classification system.
The information that follows these tables provides details on the proper use, interpretation, and limitations of the weight classification system.
The weight classification system is appropriate for adults age 18 years and older. Although an adult is defined physiologically as one who has reached his/her full growth potential, for practical purposes age 18 has been used as the lower age limit, as full growth will be reached by the majority of individuals by this age. An upper age limit has not been established. However, limitations regarding weight classification for seniors, age 65 and older, are described in Section 3.5. In addition, there are limitations to weight classification that arise from the wide variation in body builds and body proportions in individuals and in populations. These are also discussed more fully in Section 3.5. Finally, the weight classification system is not appropriate for use with pregnant and lactating women.
The weight classification system can be applied to both populations and individuals in order to:Footnote 4
A distinction must be drawn between applications of the weight classification system at the population and individual levels.
At the population level, BMI categories that range from 'underweight' to 'obese' can be applied to identify body weight patterns within the population. Prevalence estimates of different body weight levels in populations can be derived and the relative risk of morbidity and mortality determined for each BMI category. In addition, a weight classification system can identify trends in body weight patterns in the population as part of a longitudinal surveillance system.
The weight classification system can also be applied to draw comparisons of body weight patterns and health risks between populations. However, such comparisons should be interpreted with caution because the BMI or WC may not correspond to the same level of risk in different populations. For example, the influence of other factors, such as ethnicity or race, may result in differences between populations in the prevalence of disease associated with each BMI category. On the other hand, the pattern of relative risk of weight-related diseases, that is the risk between those of abnormal weight as compared to those of normal weight, is fairly consistent across populationsFootnote 4.
The information derived from body weight surveillance and associated health risks can help guide health policy decisions. It can also serve as a component in the evaluation of population-based intervention programs.
At the individual level, weight classification can be used as an initial assessment tool to identify individuals at increased relative risk for morbidity and mortality. Due to the effects of other factors, there is considerable variability among individuals in the risk associated with a specific BMI or WC categoryFootnote 16. For this reason, the estimation of an individual's health risk should not be based on measures of body weight and waist measurement alone.
Measures of BMI and WC should be components of a more comprehensive health assessment of the individual. This assessment could also include, depending on age and other factors, information on the presence of other risk factors, such as hypertension, dyslipidemia, family history of disease and individual weight history (i.e., patterns of weight gain and/or weight loss). In addition, individual health behaviours such as tobacco use, eating habits, and physical activity patterns also require assessment as do weight-related psychological and social factors.
Finally, the cut-off points included in the weight classification system are not meant to represent weight management intervention targets Footnote 14. These depend on individual characteristics.
As mentioned previously, there is a continuous relationship between gradations of BMI and risks of morbidity and mortality. This relationship can be depicted as a U or J-shaped curve. The health risk is lowest for BMIs corresponding to the bottom or flat part of the curve (the normal weight range), and increases as the curve rises at either end Footnote 14. For practical purposes, BMIs are classified into four categories with cut-off points established to define a range of BMIs for each category as shown in Table 3.
The relationship between WC and health risk is also continuous, however, there is less information, to date, to establish WC cut-off points related to different levels of health risk along the WC continuum. Because of this limitation only one WC cut-off point for men and one for women have been included in Table 4.
The BMI is an index of weight-to-height (kg/m2). Although it is high levels of body fat that are most closely linked to health risks for overweight people and low levels of fat and lean tissue that pose a risk for underweight people, methods to directly measure these tissues are not practical for widespread use. The BMI is not a direct measure of body fat or lean tissue, but it is, to date, the most widely investigated and most useful indicator of health problems that are associated with under and overweight Footnote 14.
The relationship between BMI and health risk is independent of height as differences in height are accounted for in the BMI formula Footnote 5. However, the BMI as an indicator of risk may have limitations for individuals or populations who are very tall or very short or who have very long or short limb lengths in relation to trunk measurement Footnote 14.
The relationship between BMI and health risk is also independent of sex. Although women, on average, have higher levels of body fat than men at the same BMI Footnote 14, their risk of health problems does not differ appreciably within the same BMI category Footnote 5.
To calculate the BMI, weight and height must be measured. Weight should be measured with individuals wearing light clothing and no shoes, and recorded to the nearest 0.2 kg (1/2 lb). Height should be measured with no shoes, standing erect, looking straight ahead, feet together and heels against a wall or measuring board. A horizontal bar, rectangular block of wood or another similar device should be lowered to rest flat on the top of the head. Height should be recorded to the nearest 0.5 cm (1/4 in)Footnote 17.
A body mass index chart has been provided in Appendix 7.6 for a quick determination of BMI at varying weights and heights.
BMI less than 18.5 - Underweight
A BMI in the underweight range is an indication of increased health risk. Underweight is associated with health problems such as undernutrition, osteoporosis, respiratory disease and eating disordersFootnote 18-21. Underweight may also be due to the effects of unrecognized underlying diseaseFootnote 19.
For seniors (age 65 and over), the risks associated with underweight may be evident at a BMI somewhat higher than that for younger adultsFootnote 9,Footnote 22. A BMI in the low 20's suggests a need for a further health assessment.
For young adults who have not reached full growthFootnote 14, or for adults who naturally have a very lean body buildFootnote 23, a BMI somewhat less than 18.5 is not necessarily an indication of health problems.
BMI 18.5 to 24.9 - Normal weight
A BMI in the normal range has been shown in population-wide studies to be associated with the lowest relative risk of morbidity and mortality. It should be noted that the entire range of BMIs in the "normal weight" category are indicative of low risk and the lower end of the range should not be viewed as the target weight.
BMI 25.0 to 29.9 - Overweight
Evidence from population-wide studies show that the relative risk of mortality begins to increase at a BMI of 25.0Footnote 14 Risk increases gradually as BMIs increase from 25 to 29.9. However, the BMI does not distinguish between fat and lean mass, therefore individuals with a very muscular body build may have BMIs in this range but without a body fat level associated with health risk. For seniors (age 65 and over), there is evidence to suggest that their relative risk of mortality begins to increase only in the upper levels of the overweight rangeFootnote 8,Footnote 9,Footnote 23,Footnote 24.
BMI 30 and over - Obese
The relative risk of mortality begins to rise more sharply at a BMI of 30. Therefore, BMIs of 30 and over have been categorized as the obese rangeFootnote 4. The obese range has been further divided into Obesity Class I (30.0 - 34.9), Obesity Class II (35.0 - 39.9) and Obesity Class III (40.0 and over). In general, the higher the BMI the greater the risk to health.
Excess abdominal fat is associated with health problems such as type 2 diabetes, coronary heart disease, and hypertensionFootnote 4,Footnote 15,Footnote 25-27. The WC is positively correlated with abdominal fat and is a practical indicator of health risk associated with abdominal obesityFootnote 4,Footnote 15,Footnote 28-31. WC is often used in combination with BMI. However, in some situations WC is also used as an independent indicator of health risk.
For a given WC, men and women have similar levels of abdominal fatFootnote 32,Footnote 33 but women are at higher risk than men at the same WCFootnote 4. The cut-off point for women is therefore set lower than that for men.
The WC is measured at the part of the trunk located midway between the lower costal margin (bottom of lower rib) and the iliac crest (top of pelvic bone) while the person is standing, with feet about 25-30 cm apart (10-12 in). The measurer should stand beside the individual and fit the tape snugly, without compressing any underlying soft tissues. The circumference should be measured to the nearest 0.5 cm (1/4 in), at the end of a normal expirationFootnote 14,Footnote 33. Appendix 7.7 provides an illustration of WC measurement.
The measurement of WC is recommended for those with a BMI in the 18.5 - 34.9 rangeFootnote 16,Footnote 29. WC is not considered useful in predicting increased risk among individuals with a BMI >= 35 because, typically, such individuals will exceed the WC cut-off points and measurement will not provide additional information regarding the level of riskFootnote 16.
WC's >=102 cm (40 inches) in men and >= 88 cm (35 inches) in women have been shown to be associated with substantially increased risk of diseases associated with abdominal obesity and these cut-off points have been included in this body weight classification systemFootnote 4,Footnote 29,Footnote 34.
Health risk increases along the WC continuum and may begin below the selected cut-off points. However, there is not yet the body of research needed to clearly establish a gradation of health risks and corresponding cut-off points.
The cut-off points in the current system may provide a conservative estimate of health risk, and therefore, are less likely to label people who are not at risk inaccurately but may miss some who are at risk.
Future research on WC cut-off points may result in a graded system which would require modifications to the cut-off points in this current body weight classification system.
There are limitations regarding the use of the body weight classification system that should be considered. First of all, a weight classification system provides a framework to measure body weight at one point in time. Individuals who experience weight change, either weight gain or weight loss, within or between BMI categories may also be at riskFootnote 5,Footnote 14.
Secondly, young adults who have not reached full growth, adults who naturally have a very lean body build or highly muscular adults may not be at the level of health risk indicated by their BMI categorization. Finally, other groups require special consideration with regard to weight classification. These include seniors, certain ethnic and racial groups, as well as those who are physically fit. More information on these groups is provided below.
Despite these limitations, the weight classification system established for Canadians in general is appropriate for the groups described above.
For individuals, however, further assessment procedures are needed to clarify health risks.
As noted on Table 3, research suggests that for adults age 65 and older the 'normal' range may begin somewhat above BMI 18.5 and extend into the 'overweight' range (BMI 25.0 to 29.9).
With regard to underweight, the point at which the health risks begin to increase for adults over age 65 has been shown in some studies to be at BMIs ranging from around 18.5 to the low 20sFootnote 9,Footnote 22. It has been suggested that these risks may be linked to unrecognized underlying diseaseFootnote 22. Nevertheless, BMIs in the low 20s and below in seniors suggest the need for additional health assessment.
Some research has also shown that the relative risk of mortality and morbidity in seniors with BMIs within the overweight range (BMI 25.0 to 29.9) is less than that for young and middle-aged adultsFootnote 9,Footnote 21,Footnote 35. However, the specific point where risk does increase in this category is unclear. In general, BMIs in the upper range of the overweight category are suggestive of increased relative health risk.
With regard to the obese range (BMI >=30.0), an increased relative risk of mortality has been shown among obese seniorsFootnote 9. In addition, functional limitations such as difficulty in walking short distances, carrying a light load, or standing up from an armless chair have also been demonstrated in obese seniors as compared to seniors within the normal rangeFootnote 36-38.
With regard to WC there is some evidence to suggest that WC cut-off points for seniors should differ from those for younger adultsFootnote 28,Footnote 33 and there is conflicting information on the value of using WC, as compared to BMI, to predict risk in this age groupFootnote 26,Footnote 39.
Although there is some research to suggest that health risks as indicated by BMI and WC may differ in seniors, for population purposes the current classification system is useful and recommended for this group. However, when used in the assessment of individual seniors, BMIs should be used with some flexibility as noted in Table 3. At this point in time, the WC cut-off points given in Table 4 can be used as an indication of health risk for seniors. As with other individuals, further assessment procedures will be needed to clarify health risks in individual seniors.
Population studies used to develop the body weight classification system were derived from predominantly Caucasian populations in the USA and Europe. There is evidence that certain ethnic or racial groups may differ from Caucasians in their levels of total body fat at a given BMI, in their fat distribution patterns, and in their degree of health riskFootnote 4,Footnote 40-44. Differences may be influenced in part, by differences in body build or body proportionsFootnote 4,Footnote 14.
For some groups, such as Black populations, health risks at the same BMI may be less than among CaucasiansFootnote 14,Footnote 45. For others, such as Chinese people Footnote 46-49 and people from South Asia (India, Pakistan, Bangladesh and Sri Lanka)Footnote 41,Footnote 50, the risks appear to be greater. It should be noted that urban and migrant South Asians, including South Asian Canadians, have shown a particular susceptibility to obesity, especially abdominal obesity, and related health problemsFootnote 51-53.
Among First Nations people in Canada, obesity has become a major public health problem in recent years, which has occurred in tandem with the increase in prevalence of type 2 diabetesFootnote 54. Although there are some survey data on the extent of the problem, detailed metabolic investigations as well as follow-up studies to characterize the type of obesity and long-term risks associated with different levels of BMI and/or WC have not been doneFootnote 55-57. Recent surveys also provide evidence that obesity is prevalent among Inuit people in CanadaFootnote 58 but the association between obesity and health risk is not well defined for this groupFootnote 59. More research is required to confirm the prevalence of obesity and its metabolic effects among Inuit people as well as among other Canadian Aboriginal populations.
Research in the area of race/ethnicity and body weight, body fat distribution and related health risks is in its early stages, particularly in Canada. At present, the body weight classification system established for Canadians in general is appropriate for all racial/ethnic groups within Canadian society. It is important to note, however, that some groups may be more susceptible to health problems associated with obesity than others.
Research has shown that regular physical activity can decrease the risk of several health problems and improve health and longevityFootnote 60,Footnote 61. In one long-term observational study in males, cardiorespiratory fitness, as measured by treadmill testing, was associated with reduced mortality in fit subjects compared to unfit subjects across levels of body weight and body fatness that ranged from lean to obeseFootnote 62. In addition, a recent Canadian study showed that individuals with moderate to high cardiorespiratory fitness had less abdominal obesity and less total body fat than their unfit counterparts at the same BMIsFootnote 63. It has been suggested that cardiorespiratory fitness can modify the negative effects of excess body weight and body fatFootnote 64. Broadly based long-term studies in a variety of population groups are needed to substantiate this finding.
One study in China demonstrated the positive effects of diet and/or physical activity on the prevention of type 2 diabetes in a susceptible populationFootnote 66. In each experimental group (diet only, activity only, diet/activity combined), the incidence of diabetes in both lean and overweight subjects was significantly lower than in the control group. A similar study in the U.S. also showed that lifestyle changes reduced the incidence of type 2 diabetes in persons at high riskFootnote 67.
Fitness levels and diet are important components of a comprehensive health risk assessment when applying the body weight classification system to individuals.
This section of the report provides the rationale and justification for changes made in order to update Canada's body weight classification system.
As mentioned previously, the 1988 Canadian Guidelines for Healthy WeightsFootnote 5 and the 2000 WHO weight classification systemFootnote 4 form the basis for the updated weight classification system described in this report. Table 6 illustrates similarities and differences between these three weight classification systems. More detail on the 1988 Canadian Guidelines for Healthy Weights plus an accompanying table is included in Appendix 7.8. Appendix 7.9 provides a brief synopsis of the WHO weight classification system with accompanying tables.
View Table 6: Weight classifications systems
Although there are many similarities in the three systems illustrated in Table 6, the differences between the 1988 Canadian Guidelines for Healthy Weights and the 2003 body weight classification system are significant. Changes to certain cut-off points in the BMI categories as well as the introduction of WC measurement have considerable impact on the application of the system at both the population and individual levels. The use of the system with adults over age 65 is also a significant change.
As part of the preparatory work to develop the updated weight classification system, a review of weight classification systems used in other countries, such as the USA, England, Scotland, Australia and New Zealand, was also carried outFootnote 16,Footnote 68-71. This review showed that these countries have adopted the WHO weight classification system, although in some cases with some variations.
The following section summarizes recent research that underlies decisions made in updating the Canadian body weight classification system.
In the updated body weight classification system, the lower BMI cut-off point of the 'normal' range is 18.5. This differs from work done in Canada in the 1980's which established the lower BMI cut-off point at 20 based on the available evidence at that timeFootnote 5. The WHO, on the other hand, has set this lower cut-off point at 18.5. However, epidemiological evidence to support this lower BMI cut-off point is less than for other BMI cut-off points in the updated body weight classification systemFootnote 72.
The selection of 18.5 is based partially on studies in non-western countries that investigated episodes of illness and ability to work in relation to low BMI levels. Provisional BMI ranges that were developed to define underweight (thinness) include: BMI 17-18.49 (mild thinness); BMI 16-16.99 (moderate thinness), and BMI <16 (severe thinness)Footnote 14. Furthermore, in the development of a global weight classification system, a BMI of 20 as the lower cut-off may exclude a substantial number of healthy adults in countries where daily life is more physically demanding than for adults in Western Europe and North America and where, on average, people tend to weigh lessFootnote 73.
The WHOFootnote 4 also reported that a BMI of 18.5 was chosen as the lower cut-off point of the normal range based on information discussed at an American Institute of Nutrition meeting in 1993Footnote 74. Selected epidemiological studies published since that time were reviewed during the updating processFootnote 7,Footnote 8,Footnote 9,Footnote 19,Footnote 21,Footnote 22,Footnote 75 These studies found an increased health risk with low BMIs, but different BMI cut-off points were used in these studies, making it difficult to determine a preferred lower cut-off point. Cut-off points investigated ranged from 18.5 to 22. Although the effects of smoking and pre-existing illness were controlled for in these studies, some authors suggested that the increased risks might be attributed to the effects of unrecognized underlying disease rather than to low body weight, per seFootnote 9,Footnote 19,Footnote 22. Overall, a clear consensus that 18.5 was the preferred cut-off point was not evident from these studies.
A recent study, however, examined the relationship between BMI and mortality in a representative sample of the Canadian populationFootnote 6. Based on data from the 1981 Canada Fitness Survey, researchers found a J-shaped relationship between BMI and mortality, with increased risk at BMIs below 18.5 relative to the 18.5 to 24.9 BMI range. The results were unchanged after adjusting for underlying illness by excluding deaths in the first two years of the study period. Age, sex, smoking status and alcohol consumption were included as covariates. These results support the selection of 18.5 as the lower BMI cut-off point and the use of the BMI categories as described in the updated body weight classification system.
In summary, based on evidence provided by the WHO and from recent Canadian data described above, the lower cut-off point of the 'normal' range has been lowered from 20 to 18.5.
The 2003 Canadian body weight classification system categorizes BMIs between 25.0 and 29.9 as 'overweight' and associated with increased health risk and a BMI of 30 and over as obese and associated with a high to extremely high risk of developing health problems. This is in accord with the WHO weight classification system.
In the 1988 Canadian Guidelines for Healthy Weights, it was stated that a BMI between 25 and 27 could 'lead to health problems in some people' and a BMI >27 was associated with 'increasing risk of developing health problems'. Since the publication of the 1988 Canadian Guidelines, more research has been conducted on the relationship between BMI and mortality and morbidity risk. The mortality curves generated from these studies show that, in general, relative risk of mortality begins to increase at a BMI of 25 which is in accord with the 1988 Canadian Guidelines. These studies show a more marked increase at a BMI of 30 [4,14]. In light of studies such as these, BMIs in the 25-29.9 range are categorized by WHO as the preobese range and BMI's of 30 and over as obese.
The 'obese' category was further sub-divided by WHO into Obesity Class I (30.0 - 34.9), Obesity Class II (35.0 - 39.9) and Obesity Class III (40.0 and over). This has been adopted in the 2003 Canadian body weight classification system. The subdivisions within the 'obese' category are based on the increasing health risks within this category which require different levels of interventionFootnote 4.
The waist to hip ratio was suggested as a measure of abdominal obesity in the 1988 Canadian Guidelines for Healthy WeightsFootnote 5. Recent research, however, indicates that the WC is a better and more practical correlate of abdominal obesity and related health risksFootnote 4,Footnote 15,Footnote 25,Footnote 28. Total abdominal fat includes both subcutaneous fat (under the skin) and visceral fat (around internal organs). High levels of visceral fat, in particular, have been shown to be associated with several risk factors that influence the development of diabetes and coronary heart diseaseFootnote 32,Footnote 33. Waist circumference is an indicator of both total abdominal fatFootnote 4,Footnote 28 and visceral fatFootnote 32,Footnote 33. The WC has therefore, been incorporated as an independent measure in the updated body weight classification system. Although research has shown that the WC is an important indicator of obesity-related health problemsFootnote 4,Footnote 15,Footnote 25,Footnote 28-31,Footnote 76, there is less research to date to identify accurately the most appropriate cut-off points.
The WHO provides two WC risk categories: a) increased risk for men >=94 cm and for women >=80 cm, and b) substantially increased risk for men >=102 cm and for women >=88 cmFootnote 4. These cut-off points were based on a study that measured relative risks among a sample of 2183 men and 2698 women aged 20-59 from the NetherlandsFootnote 77. They were provided as an example only by WHOFootnote 4. It was recommended that specific WC cut-off points that are appropriate for different populations be developed.
A recent study of about 10,000 Canadian men and women evaluated waist circumference cut-off points as predictors of cardiovascular risk factorsFootnote 28. The cut-off points identified (>=90 cm in men and >=80 cm in women) are comparable, particularly for women, to the figures for increased risk in the WHO system (>=94 cm in men and >=80 cm in women) and provide tentative support for these cut-off figures. Another recent study used the WC cut-off points >88 for women and >102 for men with a large sample of the U.S. population to test the appropriateness of these cut-off pointsFootnote 29. In BMI categories that ranged from normal to obese, those with WC above the cut-off points had increased risk of one or more obesity-related disorders, such as type 2 diabetes, hypertension and dyslipemia, as compared to those with WC below the cut-off points. This provides support for the WHO cut-off points for substantially increased risk (>= 88 for women and >= 102 for men). These studies are based on cross-sectional data and additional longitudinal studies are needed to support these findings.
In the updated Canadian body weight classification system, cut-off points for the WHO's 'substantially increased' level of risk were selected to prevent possible inappropriate labelling of people. However, a graded system that would differentiate between levels of risk would be a better representation of the WC/health risk continuum. As research adds to the knowledge base on appropriate WC cut-off points, the cut-off points included in the weight classification system may require modification.
The updated weight classification system does not specify an upper age limit whereas the 1988 Canadian Guidelines for Healthy Weights specified they were appropriate for adults up to 65 years of age. The WHO system, on the other hand, does not specify an upper age limit.
In studies of groups of seniors that were reviewed for this report, the findings were mixedFootnote 9,Footnote 21,Footnote 22,Footnote 24,Footnote 35,Footnote 36-38,Footnote 78,Footnote 79. Research among seniors is complicated by the heterogeneity of this population and their intrinsic multiple health risks and shorter life expectancy. It is noteworthy that, although the relative risk of health problems among overweight/ obese seniors may be lower than that among younger adults, both normal weight seniors and overweight/obese seniors experience high morbidity and mortality rates. This has led some researchers to question the value of relative risk as a reference point for this populationFootnote 16.
Additional research with this population is necessary to better understand the health risks associated with BMI levels in seniors. An upper age limit has not been included in the Canadian Guidelines for Body Weight Classification in Adults, but qualifying information has been included in this report regarding the possible limitations of weight classification for this group with regard to both overweight and underweight.
Labelling BMI ranges
The updated system provides labels for BMI ranges with weight terms such as 'underweight', 'overweight', and 'obese'. This was not done in the 1988 Canadian system due to the potential for stigmatization based on weight labels. Weight titles, however, are commonly used by professionals to describe weight patterns and trends in populations and for clinical purposes. They are also commonly used and understood by the general public.
Selection of term 'normal' for the least risk range
The term 'normal' weight as used by WHO to describe the 'least risk' category of BMIs was adopted in the updated system. The term healthy weight was considered, however, it may incorrectly imply an assurance of good health for people in this range.
Use of the term 'overweight'
In the updated system, the term 'overweight' has been selected to describe the BMI range 25.0 to 29.9. WHO, on the other hand, uses the term 'overweight' to classify all people with a BMI >= 25.0. Those in the 25.0 to 29.9 range are termed 'preobese'. In contrast, the USA has adopted the WHO weight classification system but uses the term 'overweight' to describe the BMI range 25.0 to 29.9 only. According to some experts, it should be implicitly understood that those who are classified as obese would also be overweightFootnote 80. To eliminate the potential for confusion when the term 'overweight' is used in the scientific literature, it has been suggested that it should be stipulated what is included i.e. either an all-inclusive overweight (BMI >= 25.0) or overweight but not obese (BMI 25.0-29.9)Footnote 80.
This report describes a body weight classification system for adults, and includes information on the development, interpretation, limitations and uses of this system. It has been developed collaboratively by an Expert Working Group of Canadian researchers and health care providers and by staff at Health Canada. It has also been reviewed by a wide variety of Canadian organizations from the government, academic, voluntary, and private sectors. The updated system is in accord with international standards and with those of other industrialized countries.
Throughout the report, the need for additional research in the area of body weight classification has been identified.
A weight classification system for children and youth is urgently needed. Currently, the International Obesity Task Force is working on the development of such a system and preliminary reports of this work have been publishedFootnote 81-83. This work would inform future efforts to develop a weight classification system for Canadian children and youth.
Special considerations when using weight classification with adults over age 65 have been identified throughout this report, due to evidence that suggests that this group of adults may differ from middle-aged or young adults in their relative risk of weight-related health problems. Further research with this age group is needed to clearly establish their health risks at different BMI ranges and WC measures.
The report has also discussed possible influences of ethnicity and race on weight-related health risks. Research is needed to clarify the limitations of a population-wide system with people of different ethnic and racial groups. The problem of obesity in Canadian Aboriginal peoples has also been raised in this report. Research is needed to better assess the extent of the problem in different Aboriginal peoples and clarify the association between obesity and long-term health risks at different BMI and WC levels. Canada, as a multicultural society, will need to continually appraise world literature in this area and conduct research with ethnic and racial groups in the Canadian population.
Research is also needed to clarify the effects of factors such as fitness and diet on weight-related health problems.
It is noted in the report that research on appropriate WC cut-off points is limited. Additional studies are needed to confirm the validity of the cut-off points proposed in the weight classification system and to determine whether cut-off points to identify different levels of risk can be developed. In addition, more information is needed as to whether the population-wide WC cut-off points are appropriate for different lifecycle and racial/ethnic groups.
As new research advances knowledge on body weight classification and relationships between weight, body fatness, body thinness and health, this weight classification system will require periodic reviews and updating.
The updated body weight classification system resulted from the combined efforts of staff at Health Canada and an Expert Working Group that represented a wide range of disciplines involved in research and practice related to body weight and health.
Background materials were prepared to support the process and included an initial assessment on the need to update the 1988 Canadian Guidelines for Healthy Weights. In addition, a review was undertaken of the WHO weight classification system as well as systems used in various other jurisdictions including Australia, England, New Zealand, Scotland, and the United States.
The Expert Working Group recommended that additional information be prepared in specific areas. This included information regarding body weight and health risks in the areas of underweight, ethnicity, seniors, and fitness as well as information on the use of waist circumference and appropriate cut-off points.
The Expert Working Group members and the Health Canada project team based decisions on their knowledge of evidence from the literature. Decisions were arrived at through consensus.
Drafts of the technical report were reviewed and revised by the Expert Working Group and by Health Canada staff. The last draft was also reviewed by several key stakeholders and stakeholder organizations.
Dr. Harvey Anderson
Department of Nutritional Sciences
University of Toronto
Dr. James Douketis
Department of Medicine
Dr. Heather Keller
Department of Family Relations and Applied Nutrition
University of Guelph
Dr. David Lau
Faculty of Medicine
University of Calgary
Dr. Marielle Ledoux
Département de nutrition
Université de Montréal
Dr. David Maclean
Institute for Health Research and Education
Simon Fraser University
Dr. Linda McCargar
Department of Agricultural, Food and Nutritional Science
University of Alberta
Dr. Gilles Paradis
Department of Public Health
Dr. Janet Polivy
Department of Psychology
University of Toronto
Dr. Bruce Reeder
Department of Community Health and Epidemiology
University of Saskatchewan
Dr. Kue Young
Department of Public Health Sciences
University of Toronto
Office of Nutrition Policy and Promotion
Health Products and Food Branch
Mary Bush, Director General
Consulting Nutritionists and Report Writers
Bureau of Biostatistics and Computer Applications Food Directorate
We would like to acknowledge the contributions from the Bureau of Biostatistics and Computer Applications, Centre for Chronic Disease Prevention and Control, Division of Aging & Seniors, Division of Childhood and Adolescence, First Nations and Inuit Health Branch, Fitness and Active Living Unit, Mental Health Promotion Unit and Women's Health Bureau.
Dr. Linda McCargar
"Should the 1988 Canadian Guidelines for Healthy Weights be Updated" March 2000. Available online at:
Nutrition and Healthy Eating
Barbara Davis and Stefa Katamay
"A Review of Weight Guidelines" October 2001. Available online at:
Nutrition and Healthy Eating
Barbara Davis and Laurie Ricciuto
"Background Information on Select Issues Raised at the October 2001 Meeting of the Expert Working Group on Healthy Weight Guidelines" April 2002.
Allium Consulting Group Inc.
"Stakeholder Consultation on Canadian Guidelines for Weight Classification - Results and Recommendations" November 2002
The stakeholder list includes organizations from key sectors interested in, and affected by, weight guidelines and strategies. An external consultation was held in the fall of 2002 to obtain feedback on the clarity, comprehensiveness and usefulness of the draft report.
A total of 94 organizations were sent the draft report; 49 responded.
Note: For some organizations several members contributed to a collated response on behalf of their organization.
For a quick determination of BMI (kg/m2), use a straight-edge to help locate the point on the chart where height (in or cm) and weight (lbs or kg) intersect. Read the number on the dashed line closest to this point. For example, an individual who weighs 69 kg and is 173 cm tall has a BMI of approximately 23.
The WC is measured at the part of the trunk located midway between the lower costal margin (bottom of lower rib) and the iliac crest (top of pelvic bone) while the person is standing, with feet about 25-30 cm apart (10-12 in). The measurer should stand beside the individual and fit the tape snugly, without compressing any underlying soft tissues. The circumference should be measured to the nearest 0.5 cm (1/4 in), at the end of a normal expiration.
The 1988 Canadian Guidelines for Healthy Weights were based on the seminal work of Canadian researchers during the 1980's to develop a scientifically-based system that would show an association between body weight and health based on measures that were reliable and practical to use.
BMI was chosen as the best measure on which to base weight and health according to several criteria including epidemiological validity, precision, reliability, accuracy, availability, cost, client acceptability and level of skill needed to conduct the measurement. To select appropriate cut-off points for BMIs, Canadian data were reviewed as well as prospective and retrospective studies from the international literature. Based on an analysis of the BMI in relationship to various levels of morbidity and mortality, the cut-off points for BMI categories were established.
The limitations in using BMI on its own to predict health risk were recognized, specifically its inability to estimate abdominal fat. It was suggested that health professionals use the waist-hip ratio (WHR) measure as an estimate of abdominal obesity and an indicator of mortality and morbidity risk. The cut-off points provided for WHR were tentative because limited data were available for analysis at that time. No data were available on WC.
View Table 7: Canadian Guidelines for Healthy Weights (1988)
Measurement of Waist-to-Hip Ratio (WHR) is recommended as an indicator of body fat distribution. WHR values above 1.0 in men, and above 0.8 in women are indicative of increased risk of weight-related health problems. These values are tentative, as more research is needed in this area.
Source: Health and Welfare Canada. (1988). Canadian Guidelines for Healthy Weights. Report of an Expert Group Convened by Health Promotion Directorate, Health Services and Promotion Branch. Ottawa: Health And Welfare Canada, page 27
The WHO weight classification system is based primarily on the association between BMI and mortality risk. Similar to the 1988 Canadian Guidelines for Healthy Weights, the WHO system associates different BMI categories with different levels of health risk. In order to establish BMI categories, large data sets from both European and USA studies were analyzed to determine the BMI ranges related to various levels of mortality and morbidity. Based on these analyses, the cut-off points for BMI were established.
The WHO also emphasizes the need to include WC to identify individuals and groups at increased risk of obesity-related illness due to excess abdominal fat. The waist circumference (WC) was selected based on evidence that the WC is a more practical correlate of abdominal fat and is more closely related to health risk than the WHR. The WHO cut-off points were provided as an example only with the recommendation that population-specific cut-off values should be developed.
View Table 8: WHO weight classification system (2000)
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