| Food Composition Data: A User's Perspective (1987) |
|The uses of food composition data|
|NCI food data needs: impact on coding systems|
United States studies
Within the United States, NCl's nutritional focus comprises two areas: (a) diet and cancer prevention, and (b) chemoprevention. Current and proposed projects that could benefit from the development of INFOODS include a large epidemiologic investigation, which is examining dietary patterns of the migrant Japanese in Hawaii and cancer incidence. Using epidemiologic data and sera samples collected from 1965 to 1968, incident cancer cases are being evaluated. The study also will examine the relationship between future cancer incidence and intakes of dietary fat, fibre, alcohol, dietary nitrates, salt, vegetables, and other food constituents.
A multi-institution clinical trial, now under way in eight US cities, is studying the effect of a low-fat diet (i.e. 20 per cent of total calories) on women at high risk for breast cancer. This protocol will test whether manipulation of dietary fat will slow or halt the subsequent promotion phase of cancer in women who have a predisposition for breast cancer.
The need for a comprehensive food data system such as that proposed by INFOODS is shown in studies on dietary fibre at Cornell University and the University of Wisconsin. Among the problems with existing fibre data are lack of standardized analysis techniques on representative foods, incomplete data, and lack of information about the meaning of current fibre values. Van Soest and Marlett are working to develop methods for fibre analysis and to analyse total fibre and individual dietary fibre components in US foods.
Similar dietary data problems exist for the food composition of carotenoids and retinoids. NCI supports several case-control studies that seek to demonstrate that levels of vitamin A consumption affect the development of colonic adenomatous polyps and adenocarcinoma. One three-year clinical trial using beta-carotene will attempt to slow the rate of polyp development and redevelopment. Vitamin A status will be assessed through blood plasma levels and dark adaptation tests. The advantage of using colonic adenomatous polyp formation, a pre-cancerous condition, as an endpoint in this trial is that the condition has a short development and redevelopment time in many patients.
In other related studies, vitamin A is being administered to persons with asbestosis, for treatment of lung mesothelioma, and to chronic and former smokers for prevention of lung cancer. Women at high risk for cervical dysplasia are taking retinyl acetate in two other trials.
A new area of NCI-sponsored research involves identifying, characterizing, and validating the dietary markers of past or present dietary exposure to cancer. Various problems exist in interpreting data derived from current nutritional assessment techniques. Moreover, the latency period of carcinogenesis poses several problems in gathering information about past dietary habits, namely that: (a) current dietary intakes may not be representative of past intakes, since dietary patterns change over time, and (b) our knowledge of the changing composition of foods is limited. Markers of both present and past dietary experience, therefore, will be especially useful in nutritionally focused studies in cancer epidemiology.