Although the foregoing types of study have contributed the bulk of our practical knowledge, most resources, in fact, do not go to that type of research. The lions' share goes instead to studies of disease mechanisms. This unbalanced distribution of resources has delayed vital discoveries in the area of how nutrition can prevent disease. Different types of research can be divided into two groups: "simple research," which includes the three types outlined previously; and "complex research," which includes most studies on disease mechanisms.
Complex research'most often leads not to light at the end of the tunnel but to more tunnel where the light should be. The words "simple" and "complex" refer to the degree of complexity in translating observations into practical knowledge that can be applied to problems of human health. We can illustrate this principle with the following examples. There has been much debate in the last few years regarding the role of salt in hypertension and the efficacy of a low-salt diet as a treatment for the condition. The critical evidence that has helped resolve this question is direct studies of the ,relationship between salt intake and blood pJ;essure, both those done epidemiologically and those done by intervention studies.
By contrast, the great number of studies of disease mechanisms, such as those attempting to comprehend the interaction between salt, hormone levels, and kidney function, have contributed little to the debate. Returning to the question of p-carotene and the prevention of cancer, it is difficult to find any evidence of where research into disease ,mechanisms, such as studies of carcinogen metabolism and of oncogenes; have illuminated the problem and thereby paved the way for effective changes in nutrition habits. The same may be said of the relationship between selenium and cancer risk. Although complex research has told us little of value, international correlation studies, animal experiments, and 'an intervention study have indicated that the nutrient is a potent anticarcinogen. Another example that illustrates how simple' research has given information of superior value is provided by studies of n-3 fats.
Evidence from epidemiological and intervention studies indicate that these lipids may protect against common heart disease (CHD). By contrast, the extensive body of evidence from complex research that attempts to elucidate how these lipids affect metabolism, although expensive, has done little to answer the question as to whether an increased intake of n-3 fats prevents CHD. The central aim of research into disease mechanisms is to understand the detailed functioning of the body.
This is sometimes disparagingly referred to as "reductionism" as it assumes that the whole is no more than the sum of the parts. But it may well be that nutrients and phytochemicals often induce their health-protecting effects by extremely complex interactions. For this reason, it is likely that studying substance-disease interactions one at the time may fail to show the whole picture. Perhaps instead of asking: "Do supplements of p-carotene prevent cancer and how do they work?" we should be asking: "Do vegetables prevent cancer?"
