Risk Factors | Cancer Prevention Institute of Canada

This section initiates a sequence of three highly interrelated topics: overweight, unhealthy eating, and physical inactivity. The essential link is causal. There is evidence that a large percentage of overweight and obese people can trace their excess weight directly to a persistent imbalance between energy intake (i.e., food calories) and energy expenditure (i.e., physical activity). This basic formula gets translated into a set of hypotheses related to healthcare and a balanced lifestyle:

The specific aspects of diet and activity in reference to weight control will be covered in this section. It could be argued that these two risk factors warrant a separate treatment. Unhealthy diet (likely) and physical inactivity (almost certainly) are independent risk factors for disease conditions other than obesity. In other words, there is a health benefit for an overweight person to be physically active and to consume a healthy balance of food.

Nevertheless, the interrelationship of physical activity and diet, especially in reference to body weight, stands out much more than their independent impact on health status. These three risk factors, though independent predictors of

disease and mortality, are inextricably bound together in terms of biology, personal behaviours, and social environment. This is why risk factor campaigns often integrate them (e.g., the section on Nutrition and Overweight in Healthy People 2010), as do national dietary / activity programs (e.g., the Vitality approach of Health Canada).

The reader will notice that there is significantly less research evidence presented for the topics of overweight, unhealthy eating, and physical inactivity than was presented in the preceding section on tobacco consumption and exposure to second-hand smoke. This is largely due to the fact that the relationship between smoking and adverse health effects was clearly identified many decades ago. Three studies published in 1950, one each by Levin et al [1] and Wynder and Graham[2] in the United States, and one by Doll and Hill[3] in England, ended “the age of innocence about the blithe charms of the cigarette”.[4] Thousands of research studies have probed various aspects of this relationship as well as efforts to reduce initiation rates and increase cessation rates. Understanding the relationship between obesity and adverse health outcomes has been a much more recent project. Likewise, the related and independent effects of physical activity and nutrition on health are still emerging fields of study.

Crisis and Opportunity

The overall Canadian prevalence of adult obesity (BMI>30) increased steadily between 1985 and 1998, more than doubling during the period (5.6% to 14.8%). In 1998, 3.3 million Canadians were obese. Only Quebec and British Columbia, each at 12%, had obesity rates below 15%.[5]

Based on the latest Canadian Community Health Survey (2003), almost half (48%) of the Canadian population is currently overweight (BMI>25). Of particular concern from the perspective of social determinants of health is the fact that increased poverty is associated with increased obesity rates; putting it somewhat differently, it is clear that low socioeconomic status can be a risk factor for overweight, with the strongest evidence relating to women.[7],[8] This reality adds a challenge to designing interventions that recognize health inequities.

Obesity has been strongly linked to several chronic conditions and diseases, including hypertension, high levels of cholesterol, coronary heart disease, and diabetes.[9] The motivation for prevention efforts involving a reduction of excess weight is clear. In fact, studies have shown that even a 10% weight loss can lead to substantial health benefits and extended life.[10] As will be seen below, however, weight loss cannot supersede the critical task of preventing obesity before it happens. The epidemic of obesity demands more than a rearguard action involving sometimes frustrating and frustrated attempts to lose weight.

Corresponding Epidemics

The need for intensified research into both the basic science and possible control of overweight and obesity has become very palpable in the last few years. While there have been remarkable reductions in tobacco consumption in developed countries, nutrition and physical activity authorities are alarmed that obesity represents a growing epidemic, one which is fast replacing smoking as the top public health concern in terms of chronic disease development and lowered quality of life.[11] The resulting call for action is understandable.

In spite of conceptual and practical differences between tobacco and obesity control, there are important overlaps as well, including:

1. At the individual level, some people deal with compulsive behaviour around eating which is similar to the addiction experienced by smokers; the phenomenon can be described as “using food for gratification beyond their nutritional requirement.”[12]

2. Social influences and advertising pressures affect both smokers and over-eaters and otherwise unhealthy eaters.

3. On the other hand, environmental constraints and circumstances lead some people to limit physical activity in the same way that such factors can promote smoking.

The theoretical base for the socio-ecological determinants of obesity, sometimes known collectively as the “obesogenic environment,” includes the following assumptions:

1. Individuals trying to make complex, sustained behavioural changes, or to adopt and maintain healthy behaviours in the first place, need all the help they can get;

2. Behaviours around obesity / overweight are sufficiently similar to smoking behaviours to warrant the same sort of environmental supports or, at least, the removal of impediments.

Obesogenic Environment

The circumstantial evidence is strong for implicating an obesogenic environment in the increase of obesity worldwide.[13],[14] Thus interventions in the environmental sphere may become the most powerful in the future. While the research evidence in this area is currently limited,[15] many different approaches are being actively evaluated for

preventing overweight and obesity at environmental levels, including: providing price support for healthy food, new food labelling schemes, regulating TV food advertising aimed at children, providing training on prevention to physicians, introducing nutrition standards for school meals and vending machines, regulating restaurant portions and nutritional messages on printed menus, and providing exercise facilities in workplaces.[16],[17]

Strategies to prevent weight gain in the first place are vital (i.e., primordial prevention). Any help in maintaining a healthy weight will be more cost-effective than treating obesity once it has developed.[18],[19] Some insights concerning primordial prevention in relation to children will be found in a special section later in the report.

Prevention will not always work. If excess weight is already present, individuals may well be encouraged to decrease energy intake and / or increase energy expenditure to promote weight loss (i.e., primary prevention). Social environment is important to these preventive efforts as well. Just as has occurred with smoking cessation (a form of primary prevention), comprehensive programs influencing the social context of energy intake and expenditure are vital to enhance the support for individuals who are self-initiating changes and / or being counselled for weight change.

The ultimate implication is that, whether the focus is primordial or primary prevention, multiple facets of the environment need to be changed simultaneously, from home, to work or school, to informal networks of friends, to the whole community and entire societies, in order to address obesity most profoundly.

Energy Intake vs. Expenditure

The individual approach to weight loss involving energy balance remains open to discussion and refinement. For example, the very fact that two behavioural factors contribute to excess weight raises questions about how they interact, and which one (unhealthy eating or sedentariness) is the biggest culprit. Also, how does a primarily “positive” behavioural change (i.e., more exercise) compare with one that has been, up to now, primarily a “negative” one (i.e., eat less, or at least eat less of certain foods). The physical activity category can be cast in negative terms

(e.g., watch less television or play less video games); likewise, diet change can be cast in positive terms, an advantage which may be a key driver behind campaigns to eat more fibre, vegetables and fruit. Positive or negative, the question remains which is the most effective way to go, and how do the “levers” for change differ in each case? And, unlike the relatively simple categories of “smoking” or “not smoking” (leaving aside for now different types of tobacco use and the controversial issue of cutting consumption or harm reduction), how does a personal change effort or public health campaign select an emphasis amidst the complex range of physical activities and dietary components available?

A final socio-ecological difference between physical activity and diet is that there are few active political or commercial agents telling people to exercise less (on the contrary, both business and community leaders are happy to have individuals “buy in” to exercise products and programs, up to and including new video “games” that are designed for tailored exercise routines). By comparison, there are clearly vested industrial interests who will resist appropriate changes to how food is produced and marketed. In this way, for some health advocates, the expanding battle-lines with Big Food appear to be drawn in ways that are reminiscent of the war with Big Tobacco.

Industry Responses

Alarmed by mounting media advocacy, draft legislation, and early litigation attempts, food and restaurant lobbyists are beginning to launch their counterattack. The three main thrusts of their campaign to support the status quo (or at least avoid penalties or forced changes) are:[20]

1. To maintain that the obesity epidemic and its health impacts are exaggerated.

2. To point out that any overweight problem is not so much to do with overeating, and especially not overeating certain unhealthy foods containing too much sugar or fat, but rather is more the result of physical inactivity.

In these communication efforts (which are not wholly without merit[21]), the food industry seems to be following a path very much parallel to tobacco manufacturers (indeed, adding to this conclusion, it is notable that some food and tobacco enterprises are housed under the same large corporate umbrella). The perceived corporate intransigence has spurred on recent reviews of the successes in tobacco control; this analysis has been followed by an application of the same principles and strategies to changing diets, as well as other forms of public risk factor prevention and health promotion.[22]

The pattern of interventions and stages of development from tobacco campaigns need to be adopted carefully. For example, it is possible that there may be a major departure from the tobacco control aspect of the overall smoking strategy, specifically in seeing more cooperative partnerships with the food industry. Since eating is not optional, food corporations will undoubtedly still be strong long after tobacco companies have been substantially marginalized.

Data Sources and Intervention Categories

The same pattern will be followed as elsewhere in this report, that is, consulting the results of respected review programs such as Cochrane and the Health Technology Assessment (in the UK), augmented by other published reviews as appropriate and available. As compared with the over 40 Cochrane titles related to tobacco control, there are only about 15 with some connection to weight control, and only a third of those projects have proceeded beyond the protocol stage.

Cochrane reviews-in-process have identified a range of treatment categories related to weight reduction, including: [23]

The long-term effectiveness of many of these interventions has not even been studied, let alone proven. The Cochrane reviews of even mainstream interventions such as exercise and counselling are still in process. However, measurement of effectiveness in the area of population health cannot (indeed, should not) only depend on the randomized clinical trials which are the staple of the Cochrane database (see Appendix A).

Using the best available evidence, then, the key obesity interventions will be outlined below, as well as some promising directions for trial projects and further evaluation.

The basic structure of this section on overweight / obesity will be to look at three types of initiatives to reduce the risk factor of excess weight:

As with tobacco control, a further categorization of interventions will occur under each heading, from community-based to comprehensive strategies.

[1] Levin ML, Goldstein H, Gerhardt PR. Cancer and tobacco smoking: A preliminary report. Journal of the American Medical Association 1950; 143(4): 336-8.

[2] Wynder EL, GrahamEA Tobacco smoking as a possible etiologic factor in bronchiogenic carcinoma; a study of 684 proved cases. Journal of the American Medical Association 1950; 143(4):329-36

[3] Doll R, Hill AB. Smoking and carcinoma of the lung British Medical Journal 1950; 221(2): 739-48. Questions about the adverse health effects of tobacco use go back at least to the 1600s when King James wrote A Counter-Blaste to Tobacco, published in 1604. See Kluger R. Ashes to Ashes: America’s Hundred-Year Cigarette War, the Public Health, and the Unabashed Triumph of Philip Morris. 1997 New York: Vintage Books.

[4] Kluger R. Ashes to Ashes: America’s Hundred-Year Cigarette War, the Public Health, and the Unabashed Triumph of Philip Morris. 1997 New York: Vintage Books Pg. 133.

[5] Katzmarzyk PT. The Canadian obesity epidemic, 1985-1998 Canadian Medical Association Journal 2002; 166(8): 1039-40.

[6] Tremblay MS, Katzmarzyk PT, Willms JD. Temporal Trends in Overweight and Obesity in Canada, 1981 – 1996. International Journal of Obesity 2002; 26(4): 538-43.

Tremblay MS, Willms JD. Secular Trends in the Body Mass Index of Canadian Children (correction), 1981 – 1996. Canadian Medical Association Journal 2001; 164(7): 970.

[7] Sobal J, Stunkard AJ. Socioeconomic status and obesity: a review of the literature. Psychology Bulletin. 1989; 105(2):260-75.

[8] Zhang Q, Wang Y. Socioeconomic inequality of obesity in the United States: do gender, age, and ethnicity matter? Social Science & Medicine. 2004; 58(6):1171-80.

[9] Douketis J, 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.

[10] Oster G, Thompson D, Edelsberg J et al. Lifetime health and economic benefits of weigh loss among obese persons American Journal of Public Health 1999; 89(10): 1536-42.

[11] See for example Mokdad AH, Marks JS, Stroup DF, Gerberding JL. Actual causes of death in the United States, 2000 Journal of the American Medical Association 2004; 291(10): 1238-45 in which the authors suggest that 400,000 deaths annually in the United States are attributable to poor diet and physical inactivity as compared to 430,000 attributable to tobacco. It should be noted that the calculation of the number of deaths attributable to poor diet and physical inactivity in this article are over inflated by at least 80,000 (see www.acpm.org, accessed December 2004) thus tempering the comparison with tobacco somewhat.

[12] Mercer SL, Green LW, Rosenthal AC et al. Possible lessons from the tobacco experience for obesity control American Journal of Clinical Nutrition 2003; 77(Suppl): S1073-82.

[13] Chopra M, Galbraith S, Darnton-Hill I. A global response to a global problem: the epidemic of overnutrition Bulletin of the World Health Organization 2002; 80(12): 952-8.

[14] Caterson ID, Gill TP. Obesity: epidemiology and possible prevention Best Practices & Research Clinical Endocrinology & Metabolism 2002; 16(4): 595-610.

[15] Swinburn B, Egger G. Preventive strategies against weight gain and obesity Obesity Reviews 2002; 3: 289-301.

[16] Kumanyika S, Jeffrey RW, Morabia A et al. Obesity prevention: the case for action International Journal of Obesity 2002; 26: 425-36.

[17] Swinburn B, Egger G, Raza F. Dissecting obesogenic environments: the development and application of a framework for identifying and prioritizing environmental interventions for obesity Preventive Medicine 1999; 29: 563-70.

[18] Gill T. Importance of preventing weight gain in adulthood Asia Pacific Journal of Clinical Nutrition 2002; 11(Suppl 3): S632-6.

[19] Caterson ID, Gill TP. Obesity: epidemiology and possible prevention Best Practices & Research Clinical Endocrinology & Metabolism 2002; 16(4): 595-610.

[20] A good review of food industry concerns and positions can be found within the Center for Consumer Freedom, available at http://www.consumerfreedom.com/ (accessed December 2004).

[21] A rather dramatic example of the first point, i.e., inaccurate mortality statistics, was provided by the Centres for Disease Control which recently had to retract the results published in March, 2004, concerning annual US deaths attributable to obesity, as noted in an earlier footnote. News report available at http://www.medicalnewstoday.com/medicalnews.php?newsid=16869 (accessed December 2004). As well, evidence will be presented later in the report that supports the primacy of exercise over dieting as an effective weight control measure.

[22] Mercer SL, Green LW, Rosenthal AC et al. Possible lessons from the tobacco experience for obesity control American Journal of Clinical Nutrition 2003; 77(Suppl): S1073-82.

[23] Vlassov VV. Weight reduction for reducing mortality in obesity and overweight Cochrane Database of Systematic Reviews, 2003.

[24] Dunshea-Mooij CAE, Ni Mhurchu C, Bennett D, Rodgers A. Chitosan for overweight or obesity Cochrane Database of Systematic Reviews, 2003.

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