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Increased Intake of Vegetables, but not Fruit, Reduces Risk for Hepatocellular Carcinoma: A Meta-analysis
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Gastroenterology
9 August 2014
Yang Yang, Dan Zhang, Na Feng, Guochong Chen, Jianjiang Liu, Guiping Chen,
Yuan Zhu
Abstract
Background
& Aims: The anti-cancer effects of vegetables and fruit have been investigated extensively, but the association between vegetable and fruit consumption and risk of hepatocellular carcinoma (HCC) has not been quantified. We performed a meta-analysis of observational studies to clarify the association.
Methods
We identified eligible studies, published from 1956 through May 31, 2014, by searching PubMed, Web of Science and EMBASE. Random-effects models were used to calculate summary relative risks (RRs), and dose-response analyses were conducted to quantify associations. Heterogeneity among studies was evaluated using Cochran's Q and I2 statistics.
Results
A total of 19 studies involving 1,290,045 participants and 3912 cases of HCC were included in the meta-analysis. The summary RR for HCC was 0.72 for individuals with high intake vs low intake of vegetables (95% confidence interval [CI], 0.63-0.83) and 0.92 with a daily increase in vegetable intake (100 g/day) (95% CI, 0.88-0.95). Subgroup analyses showed that this inverse association did not change regardless of history of hepatitis, alcohol drinking, smoking, or energy intake. The summary RR for HCC among individuals with high vs low intake of fruit was 0.93 (95% CI, 0.80-1.09), and 0.99 with a daily increase in fruit intake (100 g/day) (95% CI, 0.94-1.05).
Conclusions
Based on a meta-analysis, increased intake of vegetables, but not fruit, is associated with lower risk for HCC. The risk of HCC decreases by 8% for every 100 g/day increase in vegetable intake. The findings should be confirmed by future studies with validated questionnaires and strict control of confounders.
In general, both vegetables and fruit are low in fat and calories, and rich in vitamins, minerals and dietary fiber, which have been found to be inversely associated with cardiovascular disease, diabetes, and stroke35-37. However, vegetables and fruit vary widely in nutritional components, with fruit containing more calories and antioxidants such as vitamin C. Vegetables not only provide dietary fiber, and vitamins A and E, but they are also good sources of phytochemicals (e.g., isothiocyanates, glucosinolates, indole-3-carbinol, and flavonoids), which possess anti-tumor activities. Intake of cruciferous vegetables has been found to reduce the risk of colorectal cancer38, lung cancer39 and gastric cancer40. It was also recently reported that vitamin E, widely existing in vegetables, could decrease HCC risk significantly, while vitamin C and multivitamin supplements were associated with higher risk of HCC in males41. In fact, some studies suggested that too much antioxidant supplementation seemed to increase overall mortality from cancers42. We had similar results with a recent cohort study of Health Survey in England, which found that vegetables might have a more protective benefit than fruit in the general population43. Based on the above information, the different effects of vegetables and fruit might be caused by differences in their nutrient compositions
Of note, since the effects of dietary factors interact with each other, a balanced diet with proper nutrition (which includes higher intake of vegetables, fish, white meat, and coffee, and reduced intake of fat, red meat, and alcohol) is more recommended overall, especially for those patients with liver diseases49. Turati et al. recently reported that a Mediterranean diet significantly decreased the risk of HCC, which provides a new paradigm for future studies50.
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