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Plant foods versus compounds in carcinogenesis; observational versus experimental human studies
Ellen Kampman1, Ilja C W Arts, Peter C H Hollman
1Division of Human Nutrition and Epidemiology, Wageningen University and Research Centre 6700, EV Wageningen, The Netherlands. ellen.kampman@wur.nl
Abstract:
The protective role of plant foods and its constituents in cancer prevention is under renewed debate since the results of recent observational studies on colorectal cancer as well as large-scale human experimental studies on colorectal adenoma recurrence are disappointing. However, most short-term experimental human studies do show that plant foods favourably modulate potential cancer-preventive mechanisms. Which methodological pitfalls may explain the inconsistencies within and between different study designs? What are the advantages and limitations of the different study approaches? Observational studies do have the advantage to study the population at large with ultimate disease as the study endpoint. These studies are limited by the difficulty to estimate intake of individual compounds by questionnaires and the lack of biological markers of relevant exposure. Controlled experimental short-term studies in humans rely on biological markers of disease as intermediate endpoints. Relatively low sensitivity and specificity of these markers may complicate extrapolation of results. In the case of long-term and large-scale human intervention studies with disease endpoints, issues such as time, dose and duration of intervention, compliance and choice of the study population influence the interpretation of results. An integrated approach combining designs, and implementing new techniques to identify biomarkers, may clarify the role of plant foods in carcinogenesis.
Insights
Recent studies on plant foods and cancer prevention show mixed results. Methodological challenges in study designs may explain these inconsistencies, highlighting the need for integrated approaches and better biomarkers.
Area of Science:
- Nutritional Science
- Cancer Prevention Research
- Epidemiology
Background:
- The role of plant foods in cancer prevention is debated due to conflicting study outcomes.
- Observational studies on colorectal cancer and adenoma recurrence have yielded disappointing results.
- Short-term human studies often indicate favorable modulation of cancer-preventive mechanisms by plant foods.
Purpose of the Study:
- To analyze methodological pitfalls causing inconsistencies in studies on plant foods and cancer prevention.
- To evaluate the advantages and limitations of different study designs (observational, experimental).
- To propose an integrated approach for clarifying the role of plant foods in carcinogenesis.
Main Methods:
- Review of observational studies focusing on disease endpoints.
- Analysis of short-term human experimental studies using intermediate biomarkers.
- Examination of long-term, large-scale human intervention studies with disease endpoints.
Main Results:
- Observational studies are limited by difficulties in estimating compound intake and lack of exposure biomarkers.
- Short-term experimental studies rely on intermediate endpoints, which may have limited sensitivity and specificity.
- Long-term intervention studies are influenced by factors like duration, compliance, and population choice.
Conclusions:
- Methodological inconsistencies across study designs complicate the interpretation of plant food effects on cancer.
- Improved biomarker identification techniques are crucial for accurate exposure assessment.
- An integrated research approach combining diverse study designs is recommended to elucidate the role of plant foods in cancer prevention.