44. Prevention of Chronic Disease by Means of Diet and Lifestyle Changes

Interventions

Interventions aimed at changing diet and lifestyle factors include educating individuals, changing the environment, modifying the food supply, undertaking community interventions, and implementing economic policies. In most cases, quantifying the effects of the intervention is difficult, because behavioral changes may take many years and synergies are potentially important but hard to estimate in formal studies. Substantial nihilism often exists regarding the ability to change populations' diets or behaviors, but major changes are possible over extended periods of time. For example, per capita egg consumption in the United States decreased from approximately 420 to 270 per year between 1940 and 1990 following recommendations for preventing CAD (though in reality, the evidence for benefits was meager). Similarly, the prevalence of smoking, despite its being a physically addictive behavior, halved among men in the United States between 1965 and 2000. Because changing behaviors related to diet and lifestyle require sustained efforts, long-term persistence is needed. However, opportunities exist that do not require individual behavior changes, and these can lead to more rapid benefits.

Educational Interventions

Efforts to change diets, physical activity patterns, and other aspects of lifestyle have traditionally attempted to educate individuals through schools, health care providers, worksites, and general media. These efforts will continue to play an important role, but they can be strongly reinforced by policy and environmental changes.

School-based Programs

School-based programs include the roles of nutrition and physical activity in maintaining physical and mental health (box 44.3). School food services should provide healthy meals, both because they directly affect health and because they provide a special opportunity to teach by example. In many countries, school-based physical education remains a significant source of physical activity for young people. In China, 72 percent of children age 6 to 18 engage in moderate to vigorous physical activity for a median of 90 to 100 minutes per week (Tudor-Locke and others 2003). Maintaining these programs should be a high priority because they have likely contributed to the historically low rates of obesity in such countries.

Worksite Interventions

Worksite interventions can efficiently include a wide variety of health promotion activities because workers spend a large portion of their waking hours and eat a large percentage of their food there. Interventions can include educating employees; screening them for behavioral risk factors; offering incentive programs to walk, ride a bicycle, or take public transportation to work; offering exercise programs during breaks or after work; improving the physical environment to promote activity; and providing healthier foods in cafeterias (box 44.4). Worksite health promotion can result in a positive return on investment through lower health costs and fewer sick days.

Interventions by Health Care Providers

Controlled intervention trials for smoking cessation and physical activity have shown that physician counseling, especially when accompanied by supporting written material, can be efficacious in modifying behavior. Studies of dietary counseling by physicians indicate that even brief messages about nutrition can influence behavior and that the magnitude of the effect is related to the intensity of the intervention (Pignone and others 2003). Identifying patients who are overweight or obese, or who are gaining weight but are not yet overweight, is an initial step in preventing and treating overweight. However, many physicians are not well trained to measure and calculate BMI and identify weight problems.

Transportation Policy and Environmental Design

Transportation policies and the design of urban environments are fundamental determinants of physical activity and therefore influence the risks of obesity and other chronic diseases. Countries can take a number of steps to make positive changes.

Limit the Role of Automobiles

In wealthy countries, the automobile has strongly influenced the trend toward low-density, automobile-based suburban developments, many built without sidewalks. These sprawling settlements tend to have few services within walking distance and are usually not linked to public transporationt. Dependence on automobiles affects physical activity, because those who use public transportation tend to walk more. In a prospective study in eight provinces in China, 14 percent of households acquired a car between 1889 and 1997, and the likelihood of men becoming obese during the same period was twice as great in households that acquired a car than in those that did not (A. C. Bell, Ge, and Popkin 2002).

National policies strongly influence automobile use and dependency. In the United States, low taxes on gasoline, free parking, and wide streets encourage car ownership: almost 92 percent of U.S. households own at least one car, and 59 percent own two or more cars (Pucher and Dijkstra 2003). In contrast, in most of Western Europe, narrow streets, limited parking, and high gasoline prices make the costs of automobile use almost double those in the United States (Pucher and Dijkstra 2003). As a result, Europeans walk or bike more and use their cars approximately 50 percent less than their American counterparts. Investment in roads rather than in public transportation creates a vicious cycle: poor public transportation systems lead to more dependency on the automobile.

As car use grows, injuries and deaths associated with automobile accidents also grow. In China, the number of four-wheeled vehicles increased from about 60,000 to more than 50 million between 1951 and 1999, and traffic fatalities increased from about 6,000 to more than 413,000 (S. Y. Wang and others 2003). Many innovative strategies have been developed to discourage private automobile use and to promote public transportation, walking, and bicycling (see box 44.5). Singapore has long been in the lead in relation to such efforts: a combination of limiting the number of licenses issued, implementing a vehicle quota system, and introducing a road pricing system has limited personal car ownership and congestion throughout the country. Other nations and regions are now enacting similar road pricing systems or congestion taxes. For example, London's congestion charging system levies a fee of approximately US$8 per day for cars entering central London. Since its inception in 2003, the charge has reduced congestion in the city and is expected to channel funds back into the city's transportation facilities.

Unfortunately some countries, particularly China, have taken a different approach to their future transportation needs. Government initiatives that encourage families to buy automobiles include lowering taxes, simplifying registration procedures, and allowing foreign financing. In Beijing alone, residents purchased 400,000 cars in 2003.

Promote Walking and Bicycle Riding

Walking or cycling for transportation and leisure are effective and practical means of engaging in physical activity and are still the most common ways to travel in many developing countries. In Bangkok and Manila, only 25 percent of travel is by car, motorcycle, or taxi, compared with 75 percent by public transportation or walking (Pendakur 2000). In Madras, India, only 8 percent of the population travels by private, motorized transportation; 22 percent of people walk; 20 percent bike; and the rest use public transportation (Pendakur 2000). In China, approximately 90 percent of the urban population walks or rides a bicycle to work, shopping, or school each day (G. Hu and others 2002). Walking or biking is more likely to be prevalent in smaller cities—that is, those with 1 million to 5 million people—than in larger ones.

Bicycle riding and walking are also important for children's health. Most American children do not walk or bike to school, even when distances are short (box 44.6). In contrast, almost 90 percent of Chinese children under 12 walk or ride a bicycle to school (Hu 2002).

In many areas, the shift toward private car use has not yet begun and can perhaps be forestalled by policies that benefit walkers and cyclists rather than drivers. Such policies include implementing road designs that promote a safe and well-lit environment for walking and cycling, including traffic-calming measures to reduce automobile speeds.

Many Western European countries have taken steps to increase safety for cyclists and walkers. In Germany and the Netherlands, bike paths serve as travel routes, not just weekend recreational destinations as they do in the United States. The former countries have invested heavily in bike paths and have also created extensive car-free areas in cities, with well-lit sidewalks, clearly marked crosswalks, and pedestrian islands that have improved safety. Both countries have increased the number of bicycle-friendly streets (on which cars are permitted but bicycles have the right of way) and have created systems to separate streams of traffic, including cars, pedestrians, and bicycles. A meta-analysis of selected traffic-calming studies in many countries reported reductions in traffic speed, accidents, injuries, and fatalities and an increase in bicycle use and walking (Bunn and others 2003).

Design Cities and Towns to Promote Health

Handy and others' (2002) comprehensive assessment of recent research on urban planning concludes that a combination of urban design, land-use patterns, and transportation systems that promotes walking and bicycling will help create active, healthier, and more livable communities. In densely developed cities that have been built around public transportation rather than away from it, individuals are much more likely to take public transit, walk, or bicycle than in other areas and to weigh less and be less likely to suffer from hypertension (Ewing, Schieber, and Zegeer 2003; Lopez 2004; Saelens, Sallis, and Frank 2003).

Those living in walker-friendly neighborhoods also appear to be more mentally healthy and are more likely to know their neighbors, to be socially active, and to participate in the political process (Leyden 2003). In contrast, urban sprawl has been linked to decreases in mental health and social capital (Frumkin 2002) as well as anger and frustration over long commutes (Surface Transportation Policy Project 1999). Sprawl adversely affects the elderly in particular because they are unable to walk to places of interest and many cannot drive. Such isolation does not promote good physical or mental health.

The so-called smart growth movement has resulted from concerns about urban sprawl and unsustainable development and is encouraging governments worldwide to rethink how they develop new areas and redevelop older suburbs and cities. Smart growth principles include mixing land uses, using compact building designs, including a range of transportation and housing choices, building walker-friendly neighborhoods in attractive communities with a distinctive sense of place, and implementing a philosophy of directing development toward existing communities and the preservation of open space (Office of the Administrator 2001) (box 44.7).

The involvement of public health practitioners in transportation planning and building design is becoming more common. In Edinburgh, a health impact assessment conducted on proposed options for transportation policy showed the effects of specific choices on both affluent members of the community and the poor. Its recommendations, now adopted, included new spending on pedestrian safety, a citywide bicycle network, more greenways and park-and-ride programs, and more rail transportation or bus services. Priorities are to benefit pedestrians first, cyclists second, public transportation users third, freight and delivery people fourth, and car users last. Establishing criteria for building design can also lead to increases in physical activity. For example, increasing signage promoting stair use, as well as the attractiveness of the facilities themselves, encourages people to use the stairs (Boutelle and others 2001) (box 44.8).

Improved Food Supply

People's diets can be enhanced by improving the food supply. The usual position of the food industry is that it simply provides whatever consumers demand, but this argument is misleading, because the industry spends more than US$12 billion annually to influence consumer choices just within the United States and many times this amount globally. Much of this sum goes to promote foods with adverse health effects, and children are primary targets.

Improving Processing and Manufacturing

Altering the manufacturing process can rapidly and effectively improve diets because such action does not require the slow process of behavioral change. One example is eliminating the partial hydrogenation of vegetable oils, which destroys essential omega-3 fatty acids and creates trans fatty acids. European manufacturers have largely eliminated trans fatty acids from their food supply by altering production methods.

Regulations can facilitate changes in manufacturing directly or indirectly by providing an incentive for manufacturers to change their processes. For example, in 2003, the U.S. Food and Drug Administration announced that food manufacturers had to include trans fatty acid content on the standard food label. Following imposition of this requirement, several large food companies said that they would reduce or eliminate trans fats, and many more are planning to do so (U.S. Food and Drug Administration 2003). In Mauritius, the government required a change in the commonly used cooking oil from mostly palm oil to soybean oil, which changed people's fatty acid intake and reduced their serum cholesterol levels (Uusitalo and others 1996). Changes in types of fat can often be almost invisible and inexpensive. Omega-3 fatty acid intakes can be increased by incorporating oils from rapeseed, mustard, or soybean into manufactured foods, cooking oils sold for use at home, or both. Selective breeding and genetic engineering provide alternative ways to improve the healthfulness of oils by modifying their fatty acid composition.

When the consumption of processed food is high, a reduction in salt consumption will usually require changes at the manufacturing level, because processed food is a major salt source. If the salt content of foods is reduced gradually, the change is imperceptible to consumers. Coordination among manufacturers or government regulation is needed; otherwise producers whose foods are lower in salt may be placed at a disadvantage. Unfortunately, good examples are not available. Another example of improved processing would be to reduce the refining of grain products, which can be done in small, almost invisible decrements.

Fortifying Food

Food fortification has eliminated iodine deficiency, pellagra, and beriberi in much of the world. In regions where iodine deficiency remains a serious problem, fortification should be a high priority. Folic acid intake is suboptimal in many regions of both developing and developed countries. Fortifying foods with folic acid is extremely inexpensive and could substantially reduce the rates of several chronic diseases. Grain products—such as flour, rice, and pasta—are usually the best foods to fortify, and in many countries, they are already being fortified with other B vitamins. Since 1998, grain products in the United States have been fortified with folic acid, which has almost eliminated folate deficiency, and rates of neural tube defect pregnancies have declined by about 19 percent (Honein and others 2001). Where intakes of vitamins B12 and B6 are also low and contribute to elevations of homocysteine, as among vegetarian populations in India, simultaneous fortification of food with these vitamins should be considered. The effects of fortification on reducing CVD are not considered proven, but the potential benefits are huge; therefore, intervention trials to evaluate the effects of fortification should be a high priority.

Increasing the Availability and Reducing the Cost of Healthy Foods

Policies regarding the production, importation, distribution, and sale of specific foods can influence their cost and availability. Policies may be directed at the focus of agricultural research and the types of production promoted by extension services. Policies often promote grains, dairy products, sugar, and beef, whereas those that encourage the production and consumption of fruits, vegetables, nuts, legumes, whole grains, and healthy oils would tend to enhance rather than reduce health.

Promoting Healthy Food Choices and Limiting Aggressive Marketing to Children

Almost every national effort to improve nutrition incorporates the promotion of healthy food choices, such as fruits, vegetables, and legumes. Ideally, such efforts are coordinated among government groups, retailers, professional groups, and nonprofit organizations, and investment in such efforts should include the careful testing and refining of social-marketing strategies.

Another strategy is to protect consumers from aggressive marketing of unhealthy foods. Producers spend billions of dollars a year encouraging children to consume foods that are detrimental to their health. Manufacturers and fast-food chains personify food products with cartoon characters; display food brands on toys; and issue "educational" card games that subvert children's natural gift for play, story telling, and make believe. The willingness to limit advertising depends on a country's political culture, but the public clearly distinguishes between advertising aimed at adults and that targeted at children. For example, in the United States, 46 percent of adults surveyed supported restrictions on advertising to children (Blendon 2002). Restrictions can range from banning advertising to children to limiting the types of products that advertisers may promote to this audience.

Initiatives at the Community Level

Nations and regions can promote a variety of initiatives to encourage greater physical activity and better nutrition. These initiatives are likely to be most effective when they are multi-faceted and coordinated and when they are developed with the active involvement of individuals and organizations within communities (Puska and others 1998).

Many countries are undertaking efforts to educate their populations about healthy lifestyles. In the Islamic Republic of Iran, the Isfahan Healthy Heart Program, a WHO collaborating center for research and training for CVD control, prevention, and rehabilitation for cardiac patients, has developed a comprehensive, integrated community intervention that involves schools, worksites, health care facilities, food services, urban planners, and the media. Physical activity is promoted by creating safe routes for walking and bicycle riding and by organizing recreational walking that involves entire families (http://ihhp.mui.ac.ir).

South Africa's Community Health Intervention Programme, a partnership between an insurance company and an academic institution, has created programs targeted to specific age groups, including children and older adults. The program's twice-weekly classes have reduced blood pressure and increased strength and balance (Lambert, Bohlmann, and Kolbe-Alexander 2001) (box 44.9).

Singapore's Fit and Trim Program uses a multidisciplinary approach to increase physical activity and healthy diets among schoolchildren. Between 1992 and 2000, the rate of obesity declined by 13.1 to 16.6 percent for children age 11 to 12 and 15 to 16 (Toh, Cutter, and Chew 2002) (box 44.10 outlines the national program for adults).

Economic Policies

Economic policies can have important effects on behavior and choices, and these policies have been particularly useful in reducing the prevalence of smoking (see chapter 46). Policies that could influence diet and physical activity deserve careful consideration because they are rarely neutral and often support unhealthy behaviors. Consider the following examples:

• Subsidies can favor the consumption of less healthy foods, such as sugar, refined grains, beef, and high-fat dairy products as opposed to fruits, vegetables, whole grains, nuts, legumes, and fish. Poland provides a striking example of how changes in subsidies can affect health (box 44.11). Governments often subsidize foods indirectly by sheltering them from sales taxes in the recognition that they are essential; however, this logic should not extend to foods with adverse health effects, such as sugar-sweetened beverages and those high in trans fats. Legislation can make this distinction, providing a modest economic incentive for healthier choices and at the same time conveying important nutritional messages (see chapter 11).

• Use of individual automobiles is often subsidized by building and maintaining highways, providing inexpensive parking, and imposing low taxes on petroleum products that do not fully reflect their societal and environmental costs. Increasing taxes on petroleum products and subsidizing public transportation could have an important effect on choice of transportation modality, which as noted earlier, has major effects on health.

• Walking, riding bicycles, and using public transportation can be promoted by economic policies that, in addition to providing better infrastructure, include discounts on transportation fares, provide secure bicycle parking, and reduce health insurance premiums.