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Between 1991 and 1998, the prevalence of obesity increased in the US by almost 50% (1) and 55% of adults are now classified as overweight or obese (BMI >25) (2). The etiology of the rising prevalence of obesity is unclear. Evolutionary genetic changes cannot be responsible for the rapid increase in obesity rates around the world because of the short amount of time; it has taken for them to occur. Dietary factors and physical activity patterns are considered to be the major modifiable factors in obesity prevention. Low physical activity levels have been shown to be associated with greater weight gain (3). Higher physical activity levels appear to result in greater weight loss and weight loss maintenance (4,5).

Coherent and comprehensive strategies for the effective prevention and management of obesity should focus on:

• Elements of the social, cultural, physical and structural environment that affect the weight status of the population at large.
• Programs to deal with those individuals and groups who are at a particular risk for obesity and its comorbidities.
• Therapeutic programs to take care of individuals with obesity.

2. PREVENTION STRATEGIES AND GOALS

Obesity management should cover a wide range of long-term strategies ranging from prevention through weight maintenance and the management of obesity comorbidities to weight loss (6). The individual strategies are interdependent. Truly effective obesity management must address all of the strategies in a coordinated manner in a variety of settings.

Even though it is important to develop therapeutic program to treat obese individuals, more attention needs to be given to prevention activities, which hopefully will have a much greater impact on the effective long-term control of obesity. Indirect evidence from a variety of sources indicate that obesity is preventable and that the prevention of weight gain is easier, less expensive and more effective that treating obesity after it has fully developed. Currently our best options to treat obesity are combined programs involving life style modification, nutritional counseling, exercise and pharmacotherapy. The effect these therapeutic obesity programs have been reviewed elsewhere is this book (See articles by Rena Wing and Lynis Dohm). Obesity develops over time and, once it has developed, is difficult to treat. Also the health consequences of obesity are the result of the cumulative metabolic and physical stress of excess weight over a long period of time and may be not fully reversible by weight loss (7). The proportion of the population that is either overweight or obese in many developed countries is now so large that there are no longer sufficient health care resources to offer treatment to all (8). Furthermore many Insurances Companies and Health Care Programs do not consider obesity a disease and do not cover visits (dietician, physician) or pharmacotherapy for obesity.

It is important to recognize that the concept of obesity prevention does not simply mean preventing normal-weight individuals from becoming obese, but also encompasses a range of strategies that aim to prevent the progression of normal normal-weight individuals to become overweight. Efforts need also to be placed to avoid the progression of overweight to obesity and to prevent weight regain in those who have been obese in the past but who have since lost weight.

3. LEVELS OF PREVENTIVE ACTION

What are the causes of this obesity epidemic? Several factors seem to be involved. Western societies are changing their eating and exercise habits; they are eating more (9) and probably exercising less. The rising epidemic seems to reflect the profound changes in society and in behavioral patterns of communities.

3.1 Universal/Public health prevention

Societal-level interventions are critical to address the obesity problem in a population. The aim of these programs is to stabilize the level of obesity in the population, to reduce the incidence of new cases of obesity and eventually to reduce the prevalence of obesity by reducing the mean weight of the population (10). Other objectives of universal prevention include improvement in nutrition and physical activity and a reduction in the level of the population at risk of obesity and weight-related comorbidities.

Several environmental and social factors need to be taken into consideration. Between 1970 and 1994 the food supply in the United States has changed dramatically. There is less red meat on the market today than in 1970 but more chicken. There are more fruits and more vegetables and less refined sugar. Another interesting aspect of the environment is what people are being encourage to eat and by whom (11). In 1997 the total food industry spent about $45 per person in advertising. By contrast the US Department of Agriculture spent $1.5 per capita to promote healthy eating. It is Clear and worrisome that the majority of information regarding nutrition choices comes from the food industry (11).

Another significant environmental factor that may contribute to the obesity epidemic is a change in the number of meals eaten away from home (a % 70 increase) and a reduction in the amount of income spent in food in the last 20 years. These environmental factors may be in part the result that, twice as many women work outside the home than in 1950s. In addition the invention of several new appliances (washer and dryer) have made our work at home less demanding and new forms of entertainment (cable TV, internet and VCR) have contributed to development of a more a sedentary life style (11). These facts do not explain the whole story of the obesity epidemic however; they are a reminder of the importance of making changes in our daily lives before it is too late.

There have been several studies evaluating the effect of teaching people healthy habits and ways to lose weight. The results are not too encouraging. The Healthy Worker Project (HWP) (12) was a randomized trial studying worksite interventions for weight loss over a two-year period. The total participation was 20,000 subjects. The mean weight loss during intervention period was 2 kg, not a large amount but certainly enough to make public health impact given the large participation.

A second health education study was the Minnesota Heart Health Program, which lasted 10 years (13). It was designed to evaluate the effectiveness of a multi-component intervention to reduce the cardiovascular incidence of mortality.

The treatment group received information on nutrition, exercise, smoking cessation and cardiovascular risk factor reduction. The total participation was 500,000 individuals. Interestingly the educational efforts put forth by the MHHP intervention did not have a significant impact reducing the rate of weight gain over time. There was an increase in average body weight of nearly a full BMI unit (~ 3kg) in both control and experimental group. A third study developed by Jeffery at al. (14) called Pound Prevention Study evaluated a low cost educational approach to weight control that focused on reducing weight gain rather than encouraging weight loss. The educational program comprised of monthly newsletters for a three-year period encouraging reducing fat intake, eating more fruits and vegetables and increasing exercise. In spite of good participation on the POP study, the intervention was not successful in preventing weight gain. In addition, universal obesity prevention efforts have been criticized for requiring everyone, whether at high or low risk to make same changes (15).

Given the lack of success of educational methods in having a positive effect on population obesity, the University of Minnesota has evaluated the effect of concentration efforts in improving environment, as well as educational interventions.

Specifically they evaluated the effect of availability and price in the consumption of fruit and salads. Their studies showed that price reductions on low fat items increased the proportional purchase of low fat items by 9%, 39% and 93% in the 10%, 25% and 50% price reduction conditions, respectively (16). These interesting data suggests that environmental changes that would affect basic features of the food supply like availability and price, would clearly impact on society food choices and can be used as a tool to promote healthy dietary habits. In general Universal/public health prevention efforts have the potential to be the most cost-effective form of prevention of overweight and obesity, especially in areas where the prevalence of these conditions is already extremely high.

To support an understanding of the big picture of obesity causation, the International Obesity task Force has developed a "causal web" showing multiple factors influencing on energy expenditure and food intake challenging the notion of individual "free will" regarding food choices (Figure 1).

Figure 1. Causal web of societal influences on obesity prevalence. Source: International Obesity Task Force, adapted from Ritenbaugh C, Kumanyika S, Morabia A, Jeffery R, Antipatis V. 1999. http://www.iotf.org

3.2 Selective prevention

Selective prevention measures are aimed at subgroups of the population who are at high risk of developing obesity. High-risk subgroups are characterized by genetic, biological or other factors associated with increased risk of obesity. Research has clearly showed that some children and youth are at increase risk of becoming overweight adults. Obese and overweight individuals occur at higher rates in racially ethnic minority populations such as African American and Hispanic Americans, compared to White Americans in the U.S. (17,18). Diabetes, hypertension and other obesity-related chronic diseases that are prevalent among adults are becoming more common in youngsters as well (19). The percentage of children and adolescents who are overweight and obese are now the highest in history. Poor dietary habits and inactivity are reported to contribute to the increase of obesity in youth. As the most inactive generation ever in history, today's youth are at the disadvantage of having less physical education programs in school as well as unsafe recreational facilities outside of school. Physicians often feel frustrated with the limited resources that are available to treat obesity. More and more physicians are realizing the need for increasing our efforts on obesity prevention. Overweight adults want to avoid the development of obesity in their children, but they do not know how to accomplish this. In this day and age of junk food, Internet fever and decreased physical activity, we are obligated to develop a successful obesity prevention program for our adolescent population.

The Healthy People 2010 goal is to reduce the proportion of adults with a body mass index (BMI) of 30 or more by one third, from 23% to 15%. To stem the rising tide of obesity in children ages 6-19 a reduction by more than half of the proportion of children who are obese-from 11% to 5%--is targeted. These new public health aims follow a disturbing decade when the prevalence of obesity increased, in direct opposition to the Healthy People 2000 goals to reduce the prevalence of overweight individuals (20).

Unfortunately, few successful models exist for the prevention of childhood and adolescent obesity. Therefore, in the discussion that follows, we review the most logical targets for preventive efforts in family, school, and community settings. Because obesity is likely a consequence of pervasive influences that operate across many settings, the development of effective preventive interventions likely requires strategies that effect multiple settings simultaneously. The most effective strategies are likely to be those that affect both energy intake and energy expenditure, and that include elements common to several environmental settings (20). Clearly the logical models presented here are subject to modification as additional data become available. Nonetheless, they offer coherent models by which hypotheses regarding the prevention of obesity can be framed and tested.

FAMILY-BASED APPROACHES TO OBESITY PREVENTION

Dietz et al. (21) have developed an interesting model for family-based approaches to prevent obesity shown in Figure xx. This model emphasizes the need of placing a major effort on potentially modifiable family factors that affect food intake and physical activity patterns, which may promote obesity. The most substantial data identify family interactions related to food consumption as a logical approach to the prevention of obesity. Age, gender, ethnicity, social norms, socioeconomic class, and family composition, as well as parents' knowledge, attitudes, and beliefs (KAB) and children's knowledge, attitudes, and beliefs are characteristics that affect both food intake and physical activity. Efforts to change parents' knowledge, attitudes, beliefs, and practices with regard to feeding children and regulating the time children spend watching television would theoretically affect both energy intake and expenditure, and therefore represent logical targets for prevention.

Energy Intake

Energy balance occurs when energy intake equals energy expenditure. Energy intake in excess of energy expenditure results in weight gain, whereas energy expenditure in excess of intake produces weight loss. The only discretionary elements of energy balance are food intake and the energy spent on activity. To prevent obesity in children and adolescents, therefore, focus must be placed primarily on factors within family, school, and community environments that affect food intake and physical activity (21).

Over the last few decades, there have been very significant changes in food supply trends and behavior regarding food intake. There has been a decrease in percentage of energy intake from fat (22); however, the consumption of added fat (such as butter on bread, fried foods) has increased dramatically (23). While food supply data show that the per capita average number of fruit and vegetable servings has increased over the past three decades, frozen potatoes (mainly French fries) and potato chips accounted for 17.5% of all vegetable servings and fruit and vegetable intake remains below recommended levels. Per capita consumption of milk declined from 31 gallons in 1970 to 24 gallons in 1997. Concurrently, cheese consumption increased 146%, from 11 lbs per person in 1970 to 28 lbs per person in 1997. Two thirds of the cheese is used in commercially prepared products such as pizza, tacos, nachos, and fast-food sandwiches (23). The decline in milk consumption occurred concurrent with the dramatic increase in soft drink consumption. Soft drink consumption between 1977/1978 and 1994 nearly tripled among teenage boys (24). Data suggest that soft drinks are displacing milk consumption among children and adolescents (22, 24, 25).

The increasing frequency of eating out at restaurants and eating food prepared away from home has an undeniably significant influence on eating behavior. Between 1977 and 1995, the percentage of meals and snacks eaten at fast-food restaurants increased 200% (26). Use of fast-food restaurants could be associated with excess weight gain because of the high fat content of the foods offered. The most popular items are generally high in fat. For example, a large hamburger from has ~ 570 kcals and 32 g of fat; a medium order of French fries has ~450 kcal and 22 g of fat (27). Altogether, this meal has 1020 kcal and 54 g of fat; about half the total recommended daily energy requirement based on a 2000-kcal/day diet.

Away-from-home foods might encourage higher energy and fat intake than at-home foods because of larger portion sizes. People may be increasingly underestimating their portion sizes and intake as they eat out more often or eat larger portions at home or outside the home. Evidence suggests that people have trouble accurately estimating portion-size information, especially as the portion size increases (28).
As shown in Dietz's family logic model (21), family practices related to food consumption can affect food choice, food preparation, and food consumption. With respect to food choice, the qualities of foods brought into the home can increase caloric intake. For example, such calorie-dense foods as regular milk, sugar-sweetened beverages, high-fat foods, and fast foods represent potential sources of excess caloric intake. Likewise, consumption of fruits, vegetables, and whole grains may potentially offset high-calorie intake. Exposure to a variety of foods may result in an increase in caloric intake and may lead to obesity. The high rates of television advertising for food products during television programming aimed at children also influence food choice. Although no data yet link consumption of high-caloric density foods to obesity or low-caloric density foods to leanness, these consumption patterns are reasonable targets for interventions.

In young children, restricted access to certain foods appears to increase preference for those foods (29). Encouraging children to eat may paradoxically decrease the intake of the food that is being encouraged, and efforts by parents to control the food intake of children are associated with impaired regulation of caloric intake (30). A final factor that may influence food consumption inside and outside the home is family meals. Children who eat dinner with their families consume more fruits and vegetables, fewer fried foods at and away from home, and less soda than children who do not eat dinner with their families (31).

Several interventions have the potential to influence family patterns of food intake. For parents of young children, primary health care providers can offer anticipatory guidance counseling that has the potential to influence both parenting practices and the knowledge, attitudes, and beliefs of children. Anticipatory guidance constitutes a routine practice in pediatrics. Reasonable targets for such counseling include the division of responsibility between parents and children with respect to efforts to reduce food intake and avoid potential sources of excess caloric intake, such as soda, fast foods, or the calorically dense foods advertised on television (21). The most appropriate strategy is not to purchase these foods, rather than to have them in the house and restrict access to them.

Physical Activity

There have been also significant changes in the ways our children spend their leisure time. Time spent viewing television has been related to the prevalence of obesity (32), and both clinical and school-based studies have demonstrated that reductions in the amount of time spent watching television reduced weight gain in children and reduced weight among overweight young adolescents (30, 33). Although video and computer use might be expected to contribute to obesity because they are sedentary behaviors, no data yet support a causal relationship. Furthermore, this rise in the amount of time children and adolescents spend viewing television (34), increases their exposure to food advertising.

Because television offers a distraction for children at busy times in a parent's day, the design and implementation of incentives to reduce television time constitutes a major challenge. However, parental limit setting in the form of excluding televisions from children's bedrooms and regulating time spent watching television to no more than 2 h per day represents an important target for intervention. If television viewing is to constitute a realistic target for preventive efforts, alternatives to television must be available. Physical activity is likely to be increased among children with siblings and playmates or among children who live in neighborhoods where opportunities exist for safe outdoor play. Daily activities that could become part of a child's daily physical activity are walking to school or to do errands with parents. Pedestrian or neighborhood safety and community structure are likely factors that promote car use. The lack of physical activity as part of daily life, as well as the changing nature of neighborhoods and families, has contributed to the increased importance of sports participation as a source of physical activity among children and adolescents (21).

Effort should also be placed on ways to increase physical activity as part of the daily routine of children and adolescents. Several interventions have focused on increasing the frequency with which children walk to school (35). Such efforts may have additional unforeseen benefits. For example, in Chicago, where fear of crime directed at children walking to school had increased truancy rates, the communities initiated a "walking school bus," in which parents walked with the children, picking up additional children as they went (36). Not only did these efforts reduce truancy rates, crime in these neighborhoods decreased (36). Increased levels of physical activity may also prevent weight gain and clearly improve obesity-associated comorbidities such as diabetes, hypertension, and hyperlipidemia.

SCHOOL-BASED APPROACHES TO OBESITY PREVENTION

Interventions in school curricula may alter children's knowledge, attitudes, and beliefs and lead to changes in either food consumption or activity levels at school and at home.

School-based programs among elementary, middle, and high school students represent an important channel for behavioral change because of near-universal enrollment and the potential to affect behaviors of children that track (persist) into adolescence and adulthood (21). Coordinated school health programming provides a strong basis for implementing a range of effective school-based activities and environments to improve diet and increase physical activity (37). A broad range of factors within schools impacts student energy balance-energy intake and energy expenditure.

One potential dietary focus for intervention is excess consumption of sugar-sweetened beverages. Consumption has increased dramatically in past decades, coincident with the obesity epidemic, and there is experimental evidence for impact on weight gain (38). The trend toward increased availability of soft drink vending machines in schools and at work sites is a growing concern. Schools, work sites, and restaurants often have exclusive-rights contracts with specific manufacturers. In schools, the number of exclusive rights contracts for soft drinks doubled between 1997 and 1998 (37). The School Health Policies and Programs Study in 1994 (37) also documents that school-based physical education in the United States was limited, that classes rarely focused on lifetime physical activity, as recommended by the Centers for Disease Control, and that only a fraction (15%) of physical education teachers required students to develop individualized fitness programs (39).

School-based interventions generally include classroom components, teaching students and motivating them to healthier habits, following sound theoretical models. Programs have implemented environmental changes, including reductions in fat content of school lunches (40), vending machines subsidized to promote fruits and vegetables, and more active physical education programming (40, 41). School-based interventions targeting obesity have typically treated obese students, with some studies indicating effectiveness (42). Although past reviews have indicated limited effectiveness of school-wide programs in the prevention of obesity (42), these studies have addressed obesity as one of several cardiovascular disease risk factors. More recent studies have focused on obesity as an end point, and effectiveness has been documented via experimental studies in high schools, middle schools, and elementary schools (33, 43). The Planet Health intervention (43) in middle schools included an interdisciplinary curriculum, taught within existing math, science, language arts, social studies, and physical education classes. To improve energy balance, the curriculum emphasized a healthy diet (reduced fat and saturated fat) and reduced television-viewing time, replacing this inactive time with physical activity chosen by the student. The Robinson primary school intervention focused exclusively on reduction in television and video use (33). This study highlight the important role of television and video viewing as a modifiable predictor of energy imbalance, and the importance of including this component in obesity prevention programs.

An important agenda for future school-based research is to identify further modifiable behavioral and environmental variables that substantially impact obesity. A continuing issue is the limited implementation of effective school-based programs. Even through programs are found to be effective, they may have limited widespread implementation. Culturally appropriate interventions may make possible both increased effectiveness and sustained implementation (44).

3.3 Targeted prevention

Targeted prevention is directed to those with existing weight problems and those with risk of comorbidities associated with overweight.
Dr. Atkinson is reviewing this topic in Chapter 15.

4. TARGETS FOR ACTION

4.1 Increasing Physical activity

It is clear that lifestyles are becoming more and more sedentary. Over the last four decades we have seen a significant shift toward less physically demanding work, both in terms of people working in manual labor such as agriculture and in the type of work within most occupations.

There have been also a significant increase in the use of automated transport, technology at home which all contribute to less physical activity. In addition few people engage in enough exercise during leisure time to compensate for the decreases in daily energy expenditure associated with sedentary activity in other aspects of their daily routine.

Weinsier et al (45) has recently provided guidance for developing strategies to prevent weight gain or weight regain. Their study showed that the key factors that separate those who gain weight (gainers) from those who maintain weight (maintainers) over time are modifiable. Specifically, they showed that the maintainers had more muscle strength and engaged in more physical activity than did the gainers. The type of physical activity exerted by the maintainers appeared to be of relatively low intensity. This finding is important because this type of physical activity would be increased by efforts to increase activities of daily living such as walking or taking the stairs rather than by planned exercise.

Greater emphasis on improving opportunities for physical activity is clearly needed. The provision of convenient and safe exercise facilities, the allocation of time for exercise, a media focus on the role of physical activity in health promotion, workplace interventions aimed at increasing such activity, and consumer education are all methods of increasing energy expenditure.

4.2 Improving the quality of the diet

The promotion of healthy diets that are low in fat, high in complex carbohydrates and contain large amounts of fresh fruit and vegetables should be a priority in obesity prevention. However this is becoming a difficult task. As incomes rise and population become more urban, individuals become more exposed to a more varied diet with a higher proportion of fats. It is important that the population is aware of nutrient-based dietary guidelines, which advise 10% of energy from protein, 15-30% energy from fat and more than 50% from complex carbohydrates. It is important that the high carbohydrate content of low fat diets should stem from the complex carbohydrates of different vegetables, fruit and whole grains, which are more satiating for fewer calories than fatty foods and are good sources of vitamins, minerals trace elements and fiber (46).

5. WAYS TO IMPROVE THE PREVENTION AND MANAGEMENT OF OBESITY

A number of possible environmental strategies for obesity control are outlined in table 1. Obesity will not be prevented by telling individuals and communities to change their diet and exercise behaviors. What is needed is a radical improvement in the social, cultural and economic environment through the combined efforts of government, the food industry, the media, communities and individuals. Improving the standard of living of all sectors of society, especially that of minority populations should be a priority. The support of international agencies and bodies, such as FAO, UNICEF, UNDP and the World Bank, as well as non-governmental organizations is essential.