Possible role of diet in cancer: systematic review and multiple meta-analyses of dietary patterns, lifestyle factors, and cancer risk

We conducted a systematic meta-analysis of observational studies on cigarette smoking and cancer from 1961 to 2003. The aim was to quantify the risk for 13 cancer sites, recognized to be related to tobacco smoking by the International Agency for Research on Cancer (IARC), and to analyze the risk variation for each site in a systematic manner. We extracted data from 254 reports published between 1961 and 2003 (177 case-control studies, 75 cohorts and 2 nested case-control studies) included in the 2004 IARC Monograph on Tobacco Smoke and Involuntary Smoking. The analyses were carried out on 216 studies with reported estimates for 'current' and/or 'former' smokers. We performed sensitivity analysis, and looked for publication and other types of bias. Lung (RR = 8.96; 95% CI: 6.73-12.11), laryngeal (RR = 6.98; 95% CI: 3.14-15.52) and pharyngeal (RR = 6.76; 95% CI: 2.86-15.98) cancers presented the highest relative risks (RRs) for current smokers, followed by upper digestive tract (RR = 3.57; 95% CI: 2.63-4.84) and oral (RR = 3.43; 95% CI: 2.37-4.94) cancers. As expected, pooled RRs for respiratory cancers were greater than the pooled estimates for other sites. The analysis of heterogeneity showed that study type, gender and adjustment for confounding factors significantly influence the RRs estimates and the reliability of the studies. Copyright 2007 Wiley-Liss, Inc.

Recent evidence indicates that obesity and related metabolic abnormalities are associated with increased incidence or mortality for a number of cancers, including those of the colon, prostate, and pancreas. Obesity, physical inactivity, visceral adiposity, hyperglycemia, and hyperinsulinemia are relatively consistent risk factors for colon cancer and adenoma. Also, patients with type 2 diabetes mellitus have a higher risk of colon cancer. For prostate cancer, the relationship to obesity appears more complex. Obesity seems to contribute to a greater risk of aggressive or fatal prostate cancer but perhaps to a lower risk of nonaggressive prostate cancer. Furthermore, men with type 2 diabetes mellitus are at lower risk of developing prostate cancer. Long-standing type 2 diabetes increases the risk of pancreatic cancer by approximately 50%. Furthermore, over the past 6 years, a large number of cohort studies have reported positive associations between obesity and pancreatic cancer. Together with data from prediagnostic blood specimens showing positive associations between glucose levels and pancreatic cancer up to 25 years later, sufficient evidence now supports a strong role for diabetes and obesity in pancreatic cancer etiology. The mechanisms for these associations, however, remain speculative and deserve further study. Hyperinsulinemia may be important, but the role of oxidative stress initiated by hyperglycemia also deserves further attention.

The Dietary Guidelines for Americans (DGA) is published every 5 y jointly by the Department of Health and Human Services (HHS) and the USDA and provides a framework for US-based food and nutrition programs, health promotion and disease prevention initiatives, and research priorities. Summarized in this report are the methods, major conclusions, and recommendations of the Scientific Report of the 2015 US Dietary Guidelines Advisory Committee (DGAC). Early in the process, the DGAC developed a conceptual model and formulated questions to examine nutritional risk and determinants and impact of dietary patterns in relation to numerous health outcomes among individuals aged ≥2 y. As detailed in the report, an expansive, transparent, and comprehensive process was used to address each question, with multiple opportunities for public input included. Consensus was reached on all DGAC's findings, including each conclusion and recommendation, and the entire report. When research questions were answered by original systematic literature reviews and/or with existing, high-quality expert reports, the quality and strength of the evidence was formally graded. The report was organized around the following 5 themes: 1) food and nutrient intakes and health: current status and trends; 2) dietary patterns, foods and nutrients, and health outcomes; 3) diet and physical activity behavior change; 4) food and physical activity environments; and 5) food sustainability and food safety. The following 3 cross-cutting topics were addressed: 1) sodium, 2) saturated fat, and 3) added sugars. Physical activity recommendations from recent expert reports were endorsed. The overall quality of the American diet was assessed to identify overconsumed and underconsumed nutrients of public health concern. Common food characteristics of healthy dietary patterns were determined. Features of effective interventions to change individual and population diet and physical activity behaviors in clinical, public health, and community settings were identified. The report was used by the HHS and the USDA to develop the 2015 DGA.