Diet has an important impact not only on health but also on daily functioning, cognitive performance, and, perhaps, psychological well-being. Much is known about the specific dietary changes necessary to improve these factors, yet it becomes ever more clear that information about proper diet is rarely sufficient to change dietary behavior. Interventions aimed at changing diet must consider the typical dietary practices of the population in question and, as a corollary, must deal with the cultural obstacles to eating the "proper" foods. Psychological factors are paramount in setting the stage for dietary change. These include the individual's perception of being at risk, perceived benefits of a change in diet, confidence that the necessary change can be made, and the symbolic and real role food plays in a person's life. Nutrition education has traditionally focused on what changes should be made, and behavioral psychology has emphasized how to make the changes. These two fields must come together, and there must be recognition that nutrition education can provide necessary information, and behavioral change strategies can provide the necessary skills. There is now a considerable amount of information on strategies for nutrition education and on principles and techniques for behavioral change. Many intervention programs to alter dietary behavior have been undertaken. These have varied from programs aimed at an entire country, such as the National Cholesterol Education Program in the United States, to programs aimed at individuals. Although these vary considerably in size, strategy, and effects, collectively they yield valuable information on effective methods for changing behavior and for maintaining behavioral change. Programs that integrate behavioral procedures such as self-monitoring, stimulus control, coping skills, and relapse prevention appear to hold the most promise. Policy is an area that has received little attention as a means of changing dietary behavior. Government officials have made major efforts to enhance food safety, improve nutrition labeling on foods, and educate the public about a balanced diet. Much more may be possible, however. Financial incentives might be offered to increase production of healthy foods, thereby lowering cost and increasing availability. Legislation could govern food advertising and food availability (eg, vending machines) to which the entire population or selected groups (eg, children) are exposed. Existing studies on dietary adherence span different interventions, populations, disease targets, methods of evaluation, and other factors, so it is not surprising that results across studies are mixed. Enough of the studies have shown positive findings, however, to lead to the conclusion that meaningful dietary modification is possible, at least in some individuals making some dietary changes.(ABSTRACT TRUNCATED AT 400 WORDS)