S.A. Miller, Professor and Dean, Graduate School of Biomedical Sciences, University of Texas Health Science Center at San Antonio, USA
“It is surprising how difficult it has been to develop widely acceptable data relating diet and chronic disease. In spite of epidemiological and animal studies supporting many of these relationships, focused human clinical studies have often been negative or at best equivocal. There is no good explanation for this.
It has become a truism in nutrition to describe the relationship between diet and chronic disease as ‘multifactoral’ in an effort to indicate its complexity. In general, however, when we describe an event as multifactoral, we mean not only that many factors are involved in its aetiology (origin), but also that each of the factors interacts with the other dietary and non-dietary components of the environment. Although we speak of this relationship, traditional experimental designs tend to ignore it.
In the case of the relationships between diet and chronic disease, it is almost certain that several factors have to vary simultaneously for a response to be observed. The metabolic and physiologic relationships among nutrients suggest this as a possibility. Equally important may be the fact that the primary disease-related factors are ubiquitous in the environment. The role of diet, then, becomes important in modulating the expression of these primary factors, rather than providing a direct effect.
It is not surprising, therefore, that using traditional experimental approaches, results obtained may be less powerful than we expect. Indeed, it may be that only long-term prospective multinutrient studies are capable of exploring these relationships. Such studies are expensive and tedious and not often performed. If this hypothesis is true, then much greater emphasis must be placed on creative animal and epidemiological studies in the development of public policy.
Equally important, however, it emphasizes the need for continuing research in these areas; it demands that much greater support be given to exploring the relationships between nutrients and other factors in modification of the disease process, particularly at the cellular and genetic levels.”