Lenore Arab

Biomarkers of fat and fatty acid intake.

Unlike other macronutrients such as protein, the amounts and types of fat in the human diet vary tremendously across cultures and over time have changed significantly within Westernized countries. Studies of the effect that fat sources, fat amounts and changes in fat intake have on human disease are extremely difficult to conduct with traditional dietary assessment methods for a number of reasons. These include the hidden nature of many fats, the variation in fatty acids contained in foods and feed and the sensitivity of individuals to questions about fat intake in their diets. For these reasons biomarkers of fat intake are particularly desirable. Fat and fat-soluble substances have the advantages over other nutrients of a long half-life and readily accessible storage depots (in the absence of starvation, undernutrition or eating disorders). Technological advances in quantitative measurements of individual fatty acids, with the help of gas chromatography and mass spectrometry (GCMS)((3)) and high performance liquid chromatography (HPLC), made possible the study of specific isomers of minor fatty acids from small tissue samples. Technological advances also opened the gateways to the study of fats that represent less than 1% of the total fat profiles, such as decosahexanoic acid (DHA), eicosapentanoic acid (EPA) and conjugated linoleic acid (CLA). Biological advances enhanced our appreciation of the differences between fats of differing chain lengths within a family, including the saturated fats. Challenges remain, such as assessing total fat intake, discriminating the contribution of endogenously produced fats, determining how to evaluate the importance of relative versus absolute contributions of fat and accounting for the factors that influence deposition and mobilization of individual fats within and between individuals. Factors that can influence deposition and mobilization include genetic variation, disease status, lifestyle differences (i.e., alcohol consumption and smoking), circulating apolipoprotein levels and the hormonal milieu of the individual and the source tissue.

Lycopene and cardiovascular disease.

Considerable evidence suggests that lycopene, a carotenoid without provitamin A activity found in high concentrations in a small set of plant foods, has significant antioxidant potential in vitro and may play a role in preventing prostate cancer and cardiovascular disease in humans. Tomato products, including ketchup, tomato juice, and pizza sauce, are the richest sources of lycopene in the US diet, accounting for >80% of the total lycopene intake of Americans. Unlike other carotenoids, lycopene is not consistently lower among smokers than among nonsmokers, suggesting that any possible preventive activity is not as an antioxidant. Instead, lycopene may have a cholesterol synthesis-inhibiting effect and may enhance LDL degradation. Available evidence suggests that intimal wall thickness and risk of myocardial infarction are reduced in persons with higher adipose tissue concentrations of lycopene. The question of whether lycopene helps to prevent cardiovascular disease can only be answered by a trial specifically evaluating its effectiveness in this area.

Garlic and Cancer: A Critical Review of the Epidemiologic Literature

Animal and in vitro studies provide evidence of an anticarcinogenic effect of active ingredients in garlic. This review of the epidemiologic literature on garlic consumption addresses cancers of the stomach, colon, head and neck, lung, breast and prostate. Nineteen studies reported relative risk estimates for garlic consumption and cancer incidence. Site-specific case-control studies of stomach and colorectal cancer, in which multiple reports were available, suggest a protective effect of high intake of raw and/or cooked garlic. Cohort studies confirm this inverse association for colorectal cancer. Few cohort and case-control studies for other sites of cancer exist. Garlic supplements, as analyzed in four cohort studies and one case-control report, from two distinct populations, do not appear to be related to risk. Low study power, lack of variability in garlic consumption categorization within studies and poor adjustment for potential cofounders may limit the reliability of any conclusions regarding garlic supplements. However, an indication of publication bias was also found by visual inspection of a funnel plot and in a log-rank test (P = 0.004). Evidence from available studies nevertheless suggests a preventive effect of garlic consumption in stomach and colorectal cancers. The study limitations indicate the need for more definitive research and improved nutritional epidemiologic analyses of dietary data.

Green and Black Tea Consumption and Risk of Stroke: A Meta-Analysis

BACKGROUND AND PURPOSE Experimental models of stroke provide consistent evidence of smaller stroke volumes in animals ingesting tea components or tea extracts. To assess whether a similar association of black or green tea consumption with reduced risk is evident in human populations, we sought to identify and summarize all human clinical and observational data on tea and stroke. METHODS We searched PubMed and Web of Science for all studies on stroke and tea consumption in humans with original data, including estimation or measurement of tea consumption and outcomes of fatal or nonfatal stroke. Data from 9 studies involving 4378 strokes among 194 965 individuals were pooled. The main outcome was the occurrence of fatal or nonfatal stroke. We tested for heterogeneity and calculated the summary effect estimate associated with consumption of >or=3 cups of tea (green or black) per day using random-effects and fixed-effects models for the homogeneous studies. Publication bias was also evaluated. RESULTS Regardless of their country of origin, individuals consuming >or=3 cups of tea per day had a 21% lower risk of stroke than those consuming <1 cup per day (absolute risk reduction, 0.79; CI, 0.73 to 0.85). The proportion of heterogeneity not explained by chance alone was 23.8%. CONCLUSIONS Although a randomized clinical trial would be necessary to confirm the effect, this meta-analysis suggests that daily consumption of either green or black tea equaling 3 cups per day could prevent the onset of ischemic stroke.

Pooled Results From 5 Validation Studies of Dietary Self-Report Instruments Using Recovery Biomarkers for Energy and Protein Intake

We pooled data from 5 large validation studies of dietary self-report instruments that used recovery biomarkers as references to clarify the measurement properties of food frequency questionnaires (FFQs) and 24-hour recalls. The studies were conducted in widely differing US adult populations from 1999 to 2009. We report on total energy, protein, and protein density intakes. Results were similar across sexes, but there was heterogeneity across studies. Using a FFQ, the average correlation coefficients for reported versus true intakes for energy, protein, and protein density were 0.21, 0.29, and 0.41, respectively. Using a single 24-hour recall, the coefficients were 0.26, 0.40, and 0.36, respectively, for the same nutrients and rose to 0.31, 0.49, and 0.46 when three 24-hour recalls were averaged. The average rate of under-reporting of energy intake was 28% with a FFQ and 15% with a single 24-hour recall, but the percentages were lower for protein. Personal characteristics related to under-reporting were body mass index, educational level, and age. Calibration equations for true intake that included personal characteristics provided improved prediction. This project establishes that FFQs have stronger correlations with truth for protein density than for absolute protein intake, that the use of multiple 24-hour recalls substantially increases the correlations when compared with a single 24-hour recall, and that body mass index strongly predicts under-reporting of energy and protein intakes.

Nutritional Status of Folate and Colon Cancer Risk: Evidence from NHANES I Epidemiologic Follow-up Study

PURPOSE This manuscript utilized the NHANES I Epidemiologic Follow-up Study (NHEFS), a national probability sample of the U.S. non-institutionalized population, to examine whether the intake of folate at baseline is associated with colon cancer risk. METHODS The NHEFS consists of 14,407 subjects with 20 years of follow-up. Sociodemographic status, dietary information, family history of colon cancer, alcohol and aspirin use, smoking status, and body mass index (BMI) are included in the Cox proportional hazard model to examine confounding effects. RESULTS After adjusting for confounders, a marginally significant association was observed between folate intake and reduced colon cancer risk. Gender and alcohol consumption appears to have an interactive effect with this association. The stratified results suggest that dietary folate is significantly inversely associated with colon cancer in men (relative risk (RR) = 0.40, 95% confidence interval (CI) = 0.18, 0.88) who consumed more than 249 microg/day of folate and that there is a significant dose-response relationship (p = 0.03). The association did not reach statistical significance in women. Using a composite dietary profile, we found that there is a significantly increased risk for men who consumed low-folate, low-methionine, and high alcohol diets when compared to male non-drinkers who consumed high-folate and high methionine diets (RR = 2.67, 95% CI = 1.16, 6.16). CONCLUSIONS This study found significant association between folate intake and reduced colon cancer risk among men and non-drinkers, but not women or drinkers. The study supports a synergistic interaction between intakes of folate, methionine and alcohol and colon cancer risk.

Biomarkers and the measurement of fatty acids

OBJECTIVE To review the various biomarkers of dietary intakes of fatty adds in human populations, their measurement, limitations and analytical considerations. DESIGN Review of the literature. RESULTS Although there is no good biomarker of intake of total fat, a number of alternatives exist for assessing the intakes of exogenously produced fatty acids that are consumed. Adipose tissue, erythrocyte membrane concentrations and serum or plasma levels can reflect prior intakes over the past few hours to the past few years. The concentrations of individual fatty acids in these media generally reflect relative levels, and are influenced by a number of factors. Although relatively expensive to analyse, a single analysis by gas chromatography or high-performance liquid chromatography provides information on multiple fatty acids, and is superior to attempting to measure specific fatty acids using traditional dietary assessment methods. CONCLUSIONS Biomarkers of fatty acids that reflect long-term intake are available for nutritional epidemiology purposes. Analytical methods have become very accurate and able to detect and quantify smaller families, such as trans-fatty acids.

Multilevel modeling in epidemiology with GLIMMIX.

Previous work has shown that multilevel modeling can be a valuable technique for epidemiologic analysis. The complexity of using this approach, however, continues to restrict its general application. A critical factor is the lack of flexible and appropriate software for multilevel modeling. SAS provides a macro, GLIMMIX, that can be used for multilevel modeling, but that is not sufficient for a complete epidemiologic analysis. We here provide additional code to obtain epidemiologic output from GLIMMIX, illustrated with new data on diet and breast cancer from the European Community Multicenter Study on Antioxidants, Myocardial Infarction, and Breast Cancer (EURAMIC). Our results give epidemiologists an easily used tool for fitting multilevel models.

Eight self-administered 24-hour dietary recalls using the internet are feasible in African Americans and whites: the Energetics Study.

OBJECTIVE To support research and to provide food and nutrition practitioners with a strong foundation for nutrient-based counseling, there is a need for affordable automated 24-hour dietary recalls. Multiple days of intake, along with repeated reports over time, are needed to achieve stable indicators of individual intakes and to support evaluation of success in meeting dietary goals because of intraindividual intake variability. Little information has been published on subject responses, participation rates, and the perceived subject burden of repeated 24-hour recalls. Our aim was to determine the willingness of subjects to conduct eight 24-hour recalls via the Internet. DESIGN A study to validate a Web-based, automated, self-administered 24-hour recall (DietDay, Centrax Corporation, Chicago, IL). SUBJECTS/SETTING Two-hundred and sixty-one white and African-American subjects within 50 miles of the University of California-Los Angeles participated in the study. Subjects completed 3 DietDays at the study visits and another 5 days on their own. The last 2 DietDays were completed 1 and 2 months after the final clinic visit. Subjects were notified by automatic e-mail of the need for DietDay completion, and nonresponders were followed up with personalized e-mails and phone calls. RESULTS The perceived subject burden was minimal and, even after completing six recalls, 92% were willing to continue reporting their daily diets 1 and 2 months later. White subjects had a slightly higher rate of return, with 94% completing all eight recalls, compared to 91% of African-American subjects. Participants were able to access the Internet in their homes, offices, library, or homes of friends or family. It is also of interest that 82% of subjects believed the 24-hour recall was superior to a diet history in reflecting their normal diet. CONCLUSION These results open up new opportunities for food and nutrition practitioners to strengthen their nutritional counseling in an efficient and affordable manner without additional time investment.

Tea consumption and the reduced risk of colon cancer – results from a national prospective cohort study

OBJECTIVE This study examines the relationship between tea consumption and colon cancer risk in the US population. DESIGN Data from the NHANES I Epidemiologic Follow-up study (NHEFS) were used to examine the hypothesis. Cox proportional hazard models were used to examine the hypothesis of a protective effect of frequent tea consumption on colon cancer occurrence. SETTING Due to differences in the precision of the exposure data, we analysed two cohort periods based on the NHEFS. Cohort I was based on the survey conducted at the NHEFS baseline and Cohort II began at the first follow-up. SUBJECTS After excluding non-incidence cases and cases lost to follow-ups, there were 2359 tea users and 6498 non-tea users at baseline and 7656 tea users and 4514 non-tea users at the first follow-up. RESULTS : After adjusting for confounders, the relative risks of colon cancer are 0.57 (95% confidence interval (CI) 0.42, 0.78) and 0.59 (95% 1.00) for subjects who consumed <or=1.5 cups and >1.5 cups per day, respectively, compared with non-tea users in Cohort II. Although more women consumed tea and the mean intake was higher, the preventive effect of tea consumption on colon cancer was found predominantly in men. The relative risks of colon cancer are 0.41 (95% 0.66) for men who consumed <or=1.5 cups day-1 and 0.30 (95% 0.98) for >1.5 cups day-1 of tea consumption (P-value for trend <0.01). No significant results were found in Cohort I. CONCLUSIONS This study suggests an inverse association between colon cancer risk and habitual tea consumption.