Health Insights Today
January/February 2012, Volume 5, Number 1
Nutrition Update
(pdf) When reading reports on new research, it is important to remember that no single study should be seen as providing the whole truth. The following reports offer helpful clues but in most cases further research is needed before firm conclusions can be drawn.
Higher Fiber Intake Associated with Decreased Breast Cancer Risk
Dong JY, He K, Wang P, Qin LQ. Dietary fiber intake and risk of breast cancer: a meta-analysis of prospective cohort studies. American Journal of Clinical Nutrition. Sep 2011;94(3):900-905.
Background: Observational and preclinical studies suggest that dietary fiber intake may reduce the risk of breast cancer, but the results are inconclusive. Objective: We aimed to examine the association between dietary fiber intake and risk of breast cancer by conducting a meta-analysis of prospective cohort studies. Design: Relevant studies were identified by a PubMed database search through January 2011. Reference lists from retrieved articles were also reviewed. We included prospective cohort studies that reported RRs with 95% CIs for the association between dietary fiber intake and breast cancer risk. Both fixed- and random-effects models were used to calculate the summary risk estimates. Results: We identified 10 prospective cohort studies of dietary fiber intake and risk of breast cancer involving 16,848 cases and 712,195 participants. The combined RR of breast cancer for the highest compared with the lowest dietary fiber intake was 0.89 (95% CI: 0.83, 0.96), and little evidence of heterogeneity was observed. The association between dietary fiber intake and risk of breast cancer did not significantly differ by geographic region, length of follow-up, or menopausal status of the participants. Omission of any single study little changed the combined risk estimate. Dose-response analysis showed that every 10-g/d increment in dietary fiber intake was associated with a significant 7% reduction in breast cancer risk. Little evidence of publication bias was found. Conclusion: This meta-analysis provides evidence of a significant inverse dose-response association between dietary fiber intake and breast cancer risk.
Dairy and Calcium Not Linked to Weight Loss
Weaver CM, Campbell WW, Teegarden D, et al. Calcium, dairy products, and energy balance in overweight adolescents: a controlled trial. American Journal of Clinical Nutrition. Nov 2011;94(5):1163-1170.
Background: Dairy product and calcium consumption have been associated with modifying body fat and body weight in children and adults. Objective: In overweight adolescent boys and girls, we aimed to determine the effect of the doubling of habitual calcium intake to the recommended intake from dairy or calcium carbonate on energy balance and purported mechanisms including fecal fat excretion, macronutrient use, and parathyroid hormone suppression. Design: Twenty-five girls with a mean (±SD) BMI (in kg/m2) of 33 ± 5 and 17 boys with a BMI of 28 ± 5, aged 12–15 y, participated in two 3-wk controlled feeding sessions that used a crossover design in random order as a summer research camp. In one session, 756 mg Ca/d was consumed; in the other session, an additional 650 mg Ca/d was provided as dairy or calcium carbonate supplements that were matched to the control in macronutrient content. Total energy and macronutrient intakes were controlled and were the same for the 2 sessions for each subject. Primary outcome measures were energy balance, fecal fat excretion, lipid oxidation, and postprandial energy expenditure. Results: There were no effects of quantity or source of calcium on energy or fat balance, despite calcium-induced increases (P <0.01) in postprandial serum parathyroid hormone suppression. Conclusion: These data lend little evidence to support the proposed mechanisms for the relation between an increase in calcium intake from calcium carbonate or dairy and weight loss or weight maintenance in children.
Green Tea Lowers Cholesterol Levels
Zheng X-X, Xu Y-L, Li S-H, Liu X-X, Hui R, Huang X-H. Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials. American Journal of Clinical Nutrition. August 1, 2011;94(2):601-610
Background: The effect of green tea beverage and green tea extract on lipid changes is controversial.Objective: We aimed to identify and quantify the effect of green tea and its extract on total cholesterol (TC), LDL cholesterol, and HDL cholesterol. Design: We performed a comprehensive literature search to identify relevant trials of green tea beverages and extracts on lipid profiles in adults. Weighted mean differences were calculated for net changes in lipid concentrations by using fixed-effects or random-effects models. Study quality was assessed by using the Jadad score, and a meta-analysis was conducted.Results: Fourteen eligible randomized controlled trials with 1136 subjects were enrolled in our current meta-analysis. Green tea consumption significantly lowered the TC concentration by 7.20 mg/dL (95% CI: −8.19, −6.21 mg/dL; P < 0.001) and significantly lowered the LDL-cholesterol concentration by 2.19 mg/dL (95% CI: −3.16, −1.21 mg/dL; P < 0.001). The mean change in blood HDL-cholesterol concentration was not significant. Subgroup and sensitivity analyses showed that these changes were not influenced by the type of intervention, treatment dose of green tea catechins, study duration, individual health status, or quality of the study. Overall, no significant heterogeneity was detected for TC, LDL cholesterol, and HDL cholesterol; and results were reported on the basis of fixed-effects models.Conclusion: The analysis of eligible studies showed that the administration of green tea beverages or extracts resulted in significant reductions in serum TC and LDL-cholesterol concentrations, but no effect on HDL cholesterol was observed.
Eggs Associated with Increased Risk of Lethal Prostate Cancer
Richman EL, Kenfield SA, Stampfer MJ, Giovannucci EL, Chan JM. Egg, red meat, and poultry intake and risk of lethal prostate cancer in the prostate-specific antigen-era: incidence and survival. Cancer Prev Res (Phila). Dec 2011;4(12):2110-2121.
Red and processed meat may increase risk of advanced prostate cancer. Data on post-diagnostic diet and prostate cancer are sparse, but post-diagnostic intake of poultry with skin and eggs may increase risk of disease progression. Therefore, we prospectively examined total, unprocessed, and processed red meat, poultry, and eggs in relation to risk of lethal prostate cancer (e.g. men without cancer at baseline who developed distant organ metastases or died from prostate cancer during follow-up) among 27, 607 men followed from 1994-2008. We also performed a case-only survival analysis to examine post-diagnostic consumption of these foods and risk of lethal prostate cancer among the 3,127 men initially diagnosed with non-metastatic prostate cancer during follow-up. In the incidence analysis, we observed 199 events during 306,715 person-years. Men who consumed 2.5 or more eggs per week had an 81% increased risk of lethal prostate cancer compared to men who consumed less than 0.5 eggs per week (HR: 1.81; 95% confidence interval (CI): 1.13, 2.89; p-trend: 0.01). In the case-only survival analysis, we observed 123 events during 19,354 person-years. There were suggestive, but not statistically significant, positive associations between post-diagnostic poultry (HR >/=3.5 vs. <1.5 servings per week: 1.69; 95%CI: 0.96, 2.99; p-trend: 0.07) and post-diagnostic processed red meat (HR >/=3 vs. <0.5 servings per week: 1.45; 95%CI: 0.73, 2.87; p-trend: 0.08) and risk of progression of localized prostate cancer to lethal disease. In conclusion, consumption of eggs may increase risk of developing a lethal-form of prostate cancer among healthy men.