Coronary artery disease (CAD), ischemic stroke, diabetes, and some specific cancers, which until recently were common only in high-income countries, are now becoming the dominant sources of morbidity and mortality worldwide. Prospective epidemiological studies, some randomized prevention trials, and many short-term studies of intermediate endpoints such as blood pressure and lipids have revealed a good deal about the specific dietary and lifestyle determinants of major chronic diseases. A general conclusion is that reducing identified, modifiable dietary and lifestyle risk factors could prevent most cases of CAD, stroke, diabetes, and many cancers among high-income populations. These findings are profoundly important, because they indicate that these diseases are not inevitable consequences of a modern society. Furthermore, low rates of these diseases can be attained without drugs or expensive medical facilities, an outcome that is not surprising, because their rates have historically been extremely low in developing countries with few medical facilities. However, preventing these diseases will require changes in behaviors related to smoking, physical activity, and diet; investments in education, food policies, and urban physical infrastructure are needed to support and encourage these changes.
Chronic Disease Prevention
In this section, we briefly review dietary and lifestyle changes that reduce the incidence of chronic disease. The potential magnitude of benefit is also discussed.
Recommended Lifestyle Changes
Specific changes in diet and lifestyle are supportive in preventing and getting rid of Chronic Diseases. Consult your physician for a personalized diet and lifestyle plan.
Avoid Tobacco Use
Avoidance of smoking by preventing initiation or by cessation for those who already smoke is the single most important way to prevent CVD and cancer. Avoiding the use of smokeless tobacco will also prevent a good deal of oral cancer.
Maintain a Healthy Weight
Obesity is increasing rapidly worldwide. Even though obesity—a body mass index (BMI) of 30 or greater—has received more attention than overweight, overweight (BMI of 25 to 30) is typically even more prevalent and also confers elevated risks of many diseases. For example, overweight people experience a two to three fold elevation in the risks of CAD and hypertension and a more than ten fold increase in the risk of type 2 diabetes compared with lean individuals (BMI less than 23). Both overweight and obese people also experience elevated mortality from cancers of the colon, breast (postmenopausal), kidney, endometrium, and other sites. Many people with a BMI of less than 25 have gained substantial weight since they were young adults and are also at increased risk of these diseases, even though they are not technically overweight. Thus, a desirable weight for most people should be within the BMI range of 18.5 to 25.0, and preferably less than 23. Additional valuable information can be obtained by measuring waist circumference, which reflects abdominal fat accumulation. In many studies, waist circumference is a strong predictor of CAD, stroke, and type 2 diabetes, even after controlling for BMI. Views about the causes of obesity and ways to prevent or reduce it have been controversial. Diets low in fat and high in carbohydrates were believed to limit caloric intake spontaneously and thus to control adiposity, but such diets have not reduced bodyweight in trials that have lasted for a year or more. Sugar-sweetened beverages contribute significantly to the overconsumption of calories, in part because calories in fluid form appear to be poorly regulated by the body. Reductions in dietary fiber and increases in the dietary glycemic load (large amounts of rapidly absorbed carbohydrates from refined starches and sugar) may also contribute to obesity. Aspects of the food supply unrelated to its macronutrient composition are also likely to be contributing to the global rise in obesity. Inexpensive food energy from refined grains, sugar, and vegetable oils has become extremely plentiful in most countries. Food manufacturers and suppliers use carefully researched methods to make products based on these cheap ingredients maximally convenient and attractive.
Maintain Daily Physical Activity and Limit Television Watching
Contemporary life in developed nations has markedly reduced people’s opportunities to expend energy, whether in moving from place to place, in the work environment, or at home. Dramatic reductions in physical activity are also occurring in developing countries because of urbanization, increased availability of motorized transportation to replace walking and bicycle riding, and mechanization of labor. However, regular physical activity is a key element in weight control and prevention of obesity. In addition to its key role in maintaining a healthy weight, regular physical activity reduces the risk of CAD, stroke, type 2 diabetes, colon and breast cancer, osteoporotic fractures, osteoarthritis, depression, and erectile dysfunction. Important health benefits have even been associated with walking for half an hour per day, but greater reductions in risk are seen with longer durations of physical activity and more intense activity.
The number of hours of television watched per day is associated with increased obesity rates among both children and adults and with a higher risk of type 2 diabetes and gallstones. This association is likely attributable both to reduced physical activity and to increased consumption of foods and beverages high in calories, which are typically those promoted on television. Decreases in television watching reduce weight, and the American Academy of Pediatrics recommends a maximum of two hours of television watching per day.
Eat a Healthy Diet
Medical experts have long recognized the effects of diet on the risk of CVD, but the relationship between diet and many other conditions, including specific cancers, diabetes, cataracts, macular degeneration, cholelithiasis, renal stones, dental disease, and birth defects, have been documented more recently. The following list discusses six aspects of diet for which strong evidence indicates important health implications. These goals are consistent with a detailed 2003 World Health Organization (WHO) report (WHO and FAO 2003).
• Replace saturated and trans fats with unsaturated fats, including sources of omega-3 fatty acids. Replacing saturated fats with unsaturated fats will reduce the risk of CAD by reducing serum low-density lipoprotein (LDL) cholesterol. Also, polyunsaturated fats (including the long-chain omega-3 fish oils and probably alpha-linoleic acid, the primary plant omega-3 fatty acid) can prevent ventricular arrhythmias and thereby reduce fatal CAD. Trans fatty acids produced by the partial hydrogenation of vegetable oils have uniquely adverse effects on blood lipids and increase risks of CAD; on a gram-for-gram basis, both the effects on blood lipids and the relationship with CAD risk are considerably more adverse than for saturated fat. Independent of other risk factors, higher intakes of trans fat and lower intakes of polyunsaturated fat increase risk of type 2 diabetes.
• Ensure generous consumption of fruits and vegetables and adequate folic acid intake. Strong evidence indicates that high intakes of fruits and vegetables will reduce the risk of CAD and stroke.
• Consume cereal products in their whole-grain, high-fiber form. Consuming grains in a whole-grain, high-fiber form has double benefits. First, consumption of fiber from cereal products has consistently been associated with lower risks of CAD and type 2 diabetes, which may be because of both the fiber itself and the vitamins and minerals naturally present in whole grains. High consumption of refined starches exacerbates the metabolic syndrome and is associated with higher risks of CAD and type 2 diabetes. Second, higher consumption of dietary fiber also appears to facilitate weight control and helps prevent constipation.
• Limit consumption of sugar and sugar-based beverages. Sugar (free sugars refined from sugarcane or sugar beets and high-fructose corn sweeteners) has no nutritional value except for calories and, thus, has negative health implications for those at risk of overweight. Furthermore, sugar contributes to the dietary glycemic load, which exacerbates the metabolic syndrome and is related to the risk of diabetes and CAD. WHO has suggested an upper limit of 10 percent of energy from sugar, but lower intakes are usually desirable because of the adverse metabolic effects and empty calories.
• Limit excessive caloric intake from any source. Given the importance of obesity and overweight in the causation of many chronic diseases, avoiding excessive consumption of energy from any source is fundamentally important. Because calories consumed as beverages are less well-regulated than calories from solid food, limiting the consumption of sugar-sweetened beverages is particularly important.
• Limit sodium intake. The principle justification for limiting sodium is its effect on blood pressure, a major risk factor for stroke and coronary disease. WHO has suggested an upper limit of 1.7 grams of sodium per day (5 grams of salt per day).
Potential of Dietary and Lifestyle Factors to Prevent Chronic Diseases
Several lines of evidence indicate that realistic modifications of diet and lifestyle can prevent most CAD, stroke, diabetes, colon cancer, and smoking-related cancers. Less progress has been made in identifying practically modifiable causes of breast and prostate cancers.
One line of evidence is based on declines in CAD in countries that have implemented preventive programs. Rates of CAD mortality have been cut in half in several high-income countries, including Australia, the United Kingdom, and the United States. Finland provides one of the best-documented examples of a community intervention. In 1972, Finland had the world’s highest CVD mortality rate.
Other evidence derives from randomized intervention studies. These often have serious limitations for estimating the potential magnitude of benefits, because typically only one or a few factors are modified, durations are usually only a few years, and noncompliance with lifestyle change is often substantial. Nevertheless, some examples are illustrative of the potential benefit. In two randomized studies among adults at high risk of type 2 diabetes, those assigned to a program emphasizing dietary changes, weight loss, and physical activity experienced only half the risk of incident diabetes (Knowler and others 2002; Tuomilehto and others 2001). The Lyon Heart Study, conducted among those with existing heart disease, found a Mediterranean-type diet high in omega-3 fatty acids reduced recurrent infarction by 70 percent compared with an American Heart Association diet (de Lorgeril and others 1994).
A third approach is to estimate the percentage of disease that is potentially preventable by reducing multiple behavioral risk factors using prospective cohort studies. Among U.S. adults, more than 90 percent of type 2 diabetes, 80 percent of CAD, 70 percent of stroke, and 70 percent of colon cancer are potentially preventable by a combination of nonsmoking, avoidance of overweight, moderate physical activity, healthy diet, and moderate alcohol consumption (Willett 2002).
Collectively, these findings indicate that the low rates of these diseases suggested by international comparisons and time trends are attainable by realistic, moderate changes that are compatible with 21st-century lifestyles.
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. 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.
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 include the roles of nutrition and physical activity in maintaining physical and mental health. 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. 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 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. 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. 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.
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.
Cost-Effectiveness of Community-based Interventions
Population wide and community-based interventions appear to be cost-effective if they reach large populations, address high-mortality and high-morbidity diseases, and are multipronged and integrated efforts. The full costs of achieving changes in behavior and policy are often complex and difficult to estimate. Interventions may yield additional spinoff benefits. For instance, decisions to reduce children’s television viewing could easily improve school outcomes as well as reduce childhood obesity. Similarly, increasing walking and bicycle riding for transportation could reduce air pollution.