Diet and cancer prevention

Research from several sources provides strong evidence that vegetables, fruits, and whole grains, dietary fibre, certain micronutrients, some fatty acids and physical activity protect against some cancers. In contrast, other factors, such as obesity, alcohol, some fatty acids and food preparation methods may increase risks. Unravelling the multitude of plausible mechanisms for the effects of dietary factors on cancer risk will likely necessitate that nutrition research moves beyond traditional epidemiological and metabolic studies. Nutritional sciences must build on recent advances in molecular biology and genetics to move the discipline from being largely 'observational' to focusing on 'cause and effect'. Such basic research is fundamental to cancer prevention strategies that incorporate effective dietary interventions for target populations.     

Diet and prevention of colorectal cancer

There is a 20-fold difference in incidence rates of colorectal cancer between the areas of highest incidence (North America and Australia) and lowest incidence (India). Animal studies, epidemiologic research, and clinical trials continue to focus on diet in the search for responsible environmental factors. Between 1997 and 1999, a number of research areas have had considerable activity, and they provide the focus for this review. Among foods, vegetables, cereals, and soy have been topics of recent research. Nutrients from foods and supplements have also gained attention, including n-3 fatty acids, calcium, and B vitamins. Gene-environment interactions are beginning to be studied in populations. Studies of the interaction between polymorphisms in the gene for methylenetetrahydrofolate reductase (MTHFR) and dietary components for risk of both colorectal cancer and adenomatous polyps provide a glimpse into the future of diet and cancer research.     

Diet and the prevention of cancer

Cancer ranks as the second-leading cause of death in developed countries and diet has long been suspected as playing a prominent role in its etiology. As a result, a substantial amount of research has been devoted to this field of study. Given the epidemiologic and biologic credibility, it is reasonable to attempt to identify specific nutrients, foods, or combination of these that are causally related to the development of cancer. Various study designs have been employed to generate and test specific hypotheses. In this review, we approach the dietary prevention of cancer primarily from an epidemiologic perspective. We examine the growing body of evidence on dietary etiologic factors and explore the practical prospects for prevention of cancer overall. An attempt is also made to explain inconsistencies in the findings and provide ideas for future research efforts in this field.     

Diet modification and gastric cancer prevention.

The relative strengths of the etiologic factors identified for gastric cancer are discussed. On the basis of available scientific data, it is recommended that dietary prevention of gastric cancer be based on attempts to reduce the ingestion of foods with a high content of salt and to increase the intake of fresh fruits and vegetables. Other identified etiologic factors offer promise and are being investigated but do not yet justify recommendation to the general public.     

Colorectal cancer prevention: Diet, drugs, or nothing

Colorectal cancer (CRC), one of the leading causes of cancer death worldwide, is now considered the most preventable malignancy. Although an estimated 145,290 Americans were diagnosed and approximately 56,290 died of the disease, CRC death could be prevented in 28,145 cases if the American Cancer Society’s screening recommendations were followed. By virtue of endoscopic and imaging accessibility of the colorectum, along with its well-characterized pathogenesis, CRC prevention and early detection have become a reality that could significantly diminish death and suffering from cancer. Unfortunately, widespread application of current screening technologies has been difficult; progress continues as visualization of and access to the colorectum enable researchers to evaluate the activity of dietary changes, nutritional supplementation, and chemoprevention agents on genetic, molecular, and histologic colorectal carcinogenesis.     

Diet and cancer

The large differences in cancer rates among countries, striking changes in these rates among migrating populations, and rapid changes over time within countries indicate that some aspect of lifestyle or environment is largely responsible for the common cancers in Western countries. Dietary fat has been hypothesized to be the key factor because national consumption is correlated with the international differences. However, detailed analyses in large prospective studies have not supported an important role of dietary fat. Instead, positive energy balance, reflected in early age at menarche and weight gain as an adult, is an important determinant of breast and colon cancers, consistent with numerous studies in animals. As a contributor to positive energy balance, and possibly by other mechanisms, physical inactivity has also been shown to be a risk factor for these diseases and in part accounts for the international differences. Although the percentage of calories from fat in the diet does not appear related to risk of colon cancer, greater risks have been seen with higher consumption of red meat, suggesting that factors other than fat per se are important. In many case-control studies, a high consumption of fruits and vegetables has been associated with reduced risks of numerous cancers, but recent prospective studies suggest these associations may have been overstated. Among the factors in fruits and vegetables that have been examined in relation to cancer risk, present data most strongly support a benefit of higher folic acid consumption in reducing risks of colon and breast cancers. These findings have been bolstered by an association between incidence of colon cancer and a polymorphism in the gene for methylenetetrahydrofolate reductase, an enzyme involved in folic acid metabolism. The benefits of folic acid appear strongest among persons who regularly consume alcohol, which itself is associated with risk of these cancers. Numerous other aspects of diet are hypothesized to influence the risks of cancers in Western countries, but for the moment the evidence is unclear.     

Diet and pharyngeal cancer

A population-based case-control study was conducted to examine the effect of ingestion of vitamin C, carotenoids and retinol on risk of pharyngeal cancer. Data were available from 166 cases of pharyngeal cancer or their next-of-kin, and from 547 controls similar in age and sex to the cases. Odds ratios (ORs) relating consumption of vitamin C, carotenoids and retinol from foods and vitamins C and A from supplements to risk of pharyngeal cancer were calculated using multiple logistic regression analysis. After adjustment for smoking and alcohol consumption, a significant increase in risk associated with low intake of vitamin C from foods was observed. Compared to the highest quartile, the OR for the lowest quartile of intake was 2.5 (95% confidence interval, 1.5-4.2). No overall effect of dietary carotenoid or retinol consumption was noted after adjustment for smoking and alcohol. Decreasing use of either vitamin C or vitamin A supplements was associated with increasing cancer risk among the case group as a whole. However, the effect of vitamin C supplement use was substantially lower when next-of-kin respondents were excluded from analysis. Also, the OR for use of vitamin A supplements is based on a very small number of cases reporting use, and must be viewed with caution. The results of our study suggest that intake of vitamin C may be protective against pharyngeal cancer, and are consistent with the results of previous studies which reported a decreased risk of pharyngeal cancer associated with intake of fruits and vegetables.     

Diet and breast cancer

Clarification of the role of diet in breast cancer pathogenesis is important in order to identify modifiable risk factors on which to focus prevention efforts. Excess weight and weight gain in adult life are related to higher risk of postmenopausal breast cancer, and weight loss after menopause is associated with substantially reduced risk. Even moderate alcohol consumption contributes considerably to excess breast cancer risk, which can likely be mitigated with adequate folate intake. Diet during early life may play a substantial role in later cancer risk, but data are limited. In addition, physical activity and the prevention of weight gain can improve survival after a breast cancer diagnosis.     

Diet diversity and gastric cancer

It has long been suggested that a varied diet may protect against gastric cancer, in the absence, however, of definition and quantification of the issue. Thus, we considered the relationship between diet diversity (i.e., variety of food intake computed as the total number of foods consumed at least once per week) and the risk of gastric cancer using data of a case-control study conducted between 1985 and 1993 in northern Italy on 746 gastric-cancer cases below age 75 years and 2,053 controls admitted to hospital for acute, non-neoplastic, non-digestive-tract diseases. A significant inverse association was observed between various measures of food diversity and gastric cancer risk. Compared with subjects in the lowest quartile of total diversity, the multivariate odds ratios (ORs) were 0.9 for the second, 0.9 for the third and 0.7 for the highest quartiles. The inverse association was even stronger for vegetable (OR = 0.5 for the highest level) and fruit (OR = 0.6) diversity. Our findings were not explained by allowance for total calorie intake and total number of servings, besides education as an indicator of social class, and support, therefore, the concept that a more diversified and richer diet is a relevant underlying correlate of the decline in gastric cancer rates. Int. J. Cancer 72:255–257, 1997. © 1997 Wiley-Liss, Inc.     

Diet and breast cancer.

It is a general opinion that the Western diet plays a significant role in increasing the risk of breast cancer in the Western World. Recently some likely mechanisms involved in increasing the risk have been disclosed. It has been found that a Western-type diet elevates plasma levels of sex hormones and decreases the sex hormone binding globulin concentration, increasing the availability of these steroids for peripheral tissues. The same diet results in low formation by intestinal bacteria of mammalian lignans and isoflavonoid phyotestrogens from plant precursors. These diphenolic compounds seem to affect hormone metabolism and production and cancer cell growth by many different mechanisms making them strong candidates for a role as cancer protective substances. The sex hormone pattern found in connection with a Western-type diet combined with low lignan and isoflavonoid excretion was found particularly in postmenopausal breast cancer patients and omnivores living in high-risk areas, and to a lesser degree in areas with less risk. However, the pattern observed was not entirely due to diet.     

Diet and breast cancer risk reduction

The association between diet and breast cancer risk has been investigated extensively and has led to some recommendations for prevention. Research suggests that maintaining a healthy weight may reduce the risk for breast cancer after menopause. Additionally, alcohol increases the risk for breast cancer even at moderate levels of intake, and women who drink alcohol also should take sufficient folate, which can mitigate this excess risk. Interesting questions for future research include the role of soy products, red meat, energy balance, and vitamin D, with particular attention to timing of exposure in early life. Breast cancer is a heterogeneous disease, and dietary factors may differentially affect certain breast cancer subtypes; future studies should therefore attempt to characterize associations according to tumor characteristics.     

Diet and prostate cancer risk reduction

Prostate cancer is the most commonly diagnosed malignancy in males. The current body of literature supports the role of nutritional products in the reduction of prostate cancer. This review critically addresses the natural products with the greatest potential to reduce the risk of prostate cancer, including lycopene, vitamin E, selenium, vitamin D, soy and green tea. The toxicities of the dietary products are addressed. The direction of future studies lies in clarifying the effects of these products and exploring the biological mechanisms responsible for the prevention of prostate cancer.     

Diet and cancer prevention: Contributions from the European Prospective Investigation into Cancer and Nutrition (EPIC) study

We present the main findings observed to date from the European Prospective Investigation into Cancer and Nutrition (EPIC) on dietary factors associated with the most frequent cancer sites.MethodsEPIC is a multicentre prospective study carried out in 23 centres in 10 European countries: Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Spain, Sweden and the United Kingdom, including 519,978 participants (366,521 women and 153,457 men), most aged 35–70 years.ResultsWe observed the following significant associations: gastric cancer risk was inversely associated with high plasma vitamin C, some carotenoids, retinol and α-tocopherol, high intake of cereal fibre and high adhesion to Mediterranean diet, while red and processed meat were associated with increased risk. High intake of dietary fibre, fish, calcium, and plasma vitamin D were associated with a decreased risk of colorectal cancer, while red and processed meat intake, alcohol intake, body mass index (BMI) and abdominal obesity were associated with an increased risk. High intake of fruit and vegetables in current smokers were associated with a decreased risk of lung cancer. An increased risk of breast cancer was associated with high saturated fat intake and alcohol intake. In postmenopausal women, BMI was positively and physical activity negatively associated with breast cancer risk. High intake of dairy protein and calcium from dairy products and high serum concentration of IGF-I were associated with an increased risk of prostate cancer. These results contribute to scientific evidence for appropriate public health strategies and prevention activities aimed at reducing the global cancer burden.