Historically, health psychology often emphasized the role of lifestyle behaviors (like diet and exercise) in physical well-being. However, a major shift occurred with the growing scientific evidence demonstrating a direct link between psychological factors, such as chronic stress, and the functioning of the body's immune system. Analyze how this discovery of a mind-body immune connection has fundamentally reshaped the scope and intervention strategies within health psychology. Contrast the older, more limited perspective with the modern, more integrated approach.