Nutritional Risk Assessment Perspectives, Methods, and Data Challenges: Workshop Summary (2007) / Chapter Skim
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4 Establishing Relationships Between Dietary Patterns and Health Outcomes
4 Establishing Relationships Between Dietary Patterns and Health Outcomes
Pages 49-64
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From page 49... ...
He expressed the hope that eventual outcomes of this workshop will be the ranking of risks and the engagement in other opportunities for advancing the nutritional aspects of food that could improve the public's health. CHALLENGES IN ESTABLISHING RELATIONSHIPS BETWEEN FOOD PATTERNS AND HEALTH OUTCOMES Presenter: Julie Mares The relationships between diet and chronic disease differ in character from the relationships between diet and deficiency or between diet and acute disease, but the techniques available for evaluating them often do not reflect this.
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Chronic diseases develop over decades, as shown in Figure 4-1. Among people exposed to conditions that increase the risk, however, relative risks for many chronic diseases decrease with age.
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The random error is compounded with bias in studies of middle-aged and older adults whose intakes change with time and also change in response to the presence of other chronic diseases that may increase risk for the disease being studied. (Cardiovascular disease, for example, may lead to dietary change and it
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observed that dietary assessment at the baseline gave odds ratio estimates very different from those obtained from retrospective estimates of the diet consumed 10 years earlier. For this reason, it is optimal to obtain multiple estimates of dietary intake over the time period that is expected to influence the development of the disease being studied.
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When the investigators compared women of all ages, they found lower odds ratios if they excluded women with unstable diets. Other Factors That Affect the Influence of Diet on Disease Other risk factors may modify the influence of diet.
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Differences in findings from different types of studies offer an opportunity to find the reasons for those differences. Biological Plausibility Animal Models Clinical Trials and Observations Relevance to Different Magnitude of Impact Groups of People Across Diet Levels Analytic Observational Population Comparisons: Studies: Ecological Studies Cohort and Case-Control Nested Populations Migrant Populations Importance: Relative to Other Risk and Protective Factors Analytic Observational Studies: Cohort and Case-Control FIGURE 4-3 Uses of different types of studies in examining the body of evidence.
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Clinical trials complement results of observational studies. For example, the Rotterdam Eye Study showed that diets rich in the components of the supplements used in the Age-Related Macular Degeneration Study reduced the incidence of intermediate AMD by 35 percent (Van Leeuwen et al., 2005)
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• Broaden trials so that they study a variety of disease outcomes, especially intermediate stages that reflect biological mecha nisms, and a variety of dietary attributes. EVIDENCE-BASED REVIEW PROCESS TO LINK DIETARY FACTORS WITH CHRONIC DISEASE Presenter: Alice H
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This is the most important step in the process. • Identify search terms, using enough terms to identify all the rele vant literature while minimizing extraneous articles.
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were all-cause mortality, myocardial infarc tion, stroke, and sudden death. Among the inclusion criteria that were used were experimental or observational studies of at least 1-year duration with at least five human subjects, with reported original CVD outcome data, and with all sources of omega-3 fatty acid intakes evaluated.
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Kathleen Ellwood provided background information on nutrition labeling and health claims, described the process for reviewing the scientific evidence, and summarized results from selected evidence-based reviews.
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. Process for Reviewing the Scientific Evidence The process for reviewing the evidence for significant scientific agreement health claims and qualified health claims is the same; the level of supportive evidence distinguishes the two.
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Classification of Relevant Studies FDA considers intervention studies to be the "gold standard" and uses intervention studies that measure modifiable risk factors. Among the observational studies, prospective cohort studies are considered more reliable than case–control studies and cross-sectional studies.
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The prostate cancer claim language statement for food labeling is, "Very limited and preliminary scientific research suggests that eating one-half to one cup of tomatoes and/or tomato sauce a week may reduce the risk of prostate cancer." FDA concludes that there is little scientific evidence supporting the claim.
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Qualifying health claim language in this case includes "a relationship between chromium picolinate and either insulin resistance or T2D is highly uncertain." Green Tea and Breast Cancer A review of the evidence identified three credible observational studies relating green tea intake to the risk of breast cancer. Two of these were prospective cohort studies that showed no relationship, and one was a case–control study that showed a beneficial relationship.
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64 NUTRITIONAL RISK ASSESSMENT Concluding Remarks Kathleen Ellwood encouraged participants to visit the FDA website for more detailed information on this topic. OPEN DISCUSSION Moderator: Michael Doyle The key points made during the open discussion have been incorporated into Chapter 6, Perspectives on Challenges and Solutions: Summary Remarks and Suggested Next Steps.
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