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Randomized clinical trial data are capable of providing strong experimental evidence to establish causal relationships between functional food components and health and disease/disease risk. However, clinical studies must be well designed in order to optimize the quality of the data they provide. The purpose of this review is to identify design elements that maximize the quality of clinical trials examining the efficacy of functional foods. Both observational studies and experimental trials can provide useful data for identifying diet-disease relationships. Two experimental designs are conventionally used: parallel and crossover. Each of these designs possesses advantages and disadvantages. For certain functional ingredients, selection of an appropriate control arm is straightforward, while for others it is challenging. Studies should be short enough to optimize subject compliance, be cost effective, and avoid high subject dropout rates, while being lengthy enough to ensure biological efficacy. The dose, frequency, and diurnal timing of intake of the active food ingredient all need to be chosen carefully. Randomized clinical trials testing the efficacy of functional foods may use both validated and emerging surrogate endpoints and should employ suitable statistical tests for data analysis. Paying attention to all these factors is crucial to the design of quality clinical trials that reliably evaluate food-health relationship validity. Accordingly, clinical studies that incorporate the optimal design elements discussed will yield robust results appropriate for the substantiation of health claims on functional foods. doi: 10.1111/j.1753-4887.2010.00308.x

Phytochemicals present in food have shown significant prospects in the treatment and management of a vast array of human diseases. Resveratrol is a stilbene-type aromatic phytoalexin predominantly found in grapes, peanuts, berries, turmeric, and other food products. Resveratrol has been reported to exhibit several physiological activities including anticancer and anti-inflammatory activities in vitro and in experimental animal models, as well as in humans. Anticancer activity of this compound is mainly due to induction of apoptosis via several pathways, as well as alteration of gene expressions, all leading to a decrease in tumor initiation, promotion, and progression. Resveratrol exhibits anti-inflammatory activity through modulation of enzymes and pathways that produce mediators of inflammation and also induction of programmed cell death in activated immune cells. Resveratrol has been shown to produce no adverse effects, even when consumed at high concentrations. Hence, resveratrol possesses good potential to be used as an adjunctive or alternative therapy for cancer and inflammatory diseases.

Conjugated linoleic acids (CLA) are positional and geometric isomers of linoleic acid. In animals, CLA consumption reduces body fat but results in humans are less conclusive. This review of the literature on CLA and loss of body fat or body weight in humans was conducted to explore the reasons for the discrepancy between animal and clinical trials. It indicates that the incongruity between human and animal data is largely related to methodological differences in the experimental design, including age and gender and, to a lesser extent, to CLA dose and isomers. The relatively unknown metabolic fate of CLA in humans may also be a contributing factor that helps explain the lack of consistency for CLA efficacy across studies.

ATP-binding cassette (ABC) transporters function in the homeostasis of lipids. Dysfunction of ABC transporters is frequently associated with disease. This review examines links between polymorphisms of ABC G5 (ABCG5) and G8 (ABCG8) transporter genes to hypercholesterolemia and to gallstone disease risk. Various polymorphisms (A632V, T400K, D19H, M429V, and C54Y) in the ABCG8 and ABCG5 (Q604E) gene have been found to be associated with several facets of cholesterol metabolism, including baseline cholesterol level, cholesterol kinetics, individual responsiveness of plasma cholesterol to dietary and pharmaceutical interventions for hypercholesterolemia, and increased risk of gallstones. Clearly, the ABCG5 and ABCG8 genes play an important role in cholesterol homeostasis. However, more research is needed to establish how specific polymorphisms of these genes confer to higher risk of these diseases.

Recently, it has been questioned whether elevated levels of circulating plant sterols increase the risk of coronary heart disease (CHD). To date, no definitive conclusions regarding such a relationship have been reached, nor have there been any studies summarizing the factors that contribute to the observed elevations in plant sterol concentrations in plasma. Thus, the purpose of this review is to systematically compare the plant sterol levels of subjects from the general population and to describe factors that contribute to the variations observed. The question of whether elevated plasma concentrations of plant sterols are associated with an increased risk of CHD was also assessed. Results indicate that the key factors accounting for variations in circulating plant sterol concentrations include: apolipoprotein E phenotypes, ATP-binding cassette transporter polymorphisms, use of statin drugs, presence of metabolic syndrome, dietary intake of plant sterols, gender, and analytical techniques used in the measurement of plant sterols in the plasma. An analysis of the studies examining the relationship between circulating levels of plant sterols and CHD risk in non-sitosterolemic populations revealed no clear associations. Furthermore, it was shown that the above-mentioned factors play an important role in determining the levels of plant sterols in plasma. Since these factors may act as potential confounders, they must be controlled for before more solid conclusions can be reached. Key words: blood concentrations, coronary heart disease, cholesterol, plant sterols doi: 10.1301/nr.2006.sept.385-402

Many studies have attempted to identify specific positive health effects of probiotics. One of the challenges in generalizing health effects of probiotics is that different strains exert disparate effects on human health. As a result, the efficacy of one strain or species cannot necessarily be inferred from another. The objective of this review is to examine the current scientific literature that could be used as the basis for potential health claims. More specifically, this paper will review existing evidence of different probiotic strains to prevent and treat diarrhea, treat irritable bowel syndrome (IBS), treat inflammatory bowel disease, and prevent colon cancer. The strongest evidence is related to the use of Lactobacillus rhamnosus GG in the prevention and treatment of rotavirus-associated diarrhea. Further examination of the literature also shows promise in the treatment of some forms of IBS with probiotics. Future studies that use consistent supplementation regimes will allow more definitive conclusions to be drawn on the effects of probiotics on IBS, inflammatory bowel disease, and colon cancer. Key words: colon cancer, diarrhea, inflammatory bowel disease, irritable bowel syndrome, probiotic bacteria

Policosanols are a mixture of aliphatic alcohols derived from purified sugar cane. When administered at 5 to 20 mg/day, policosanols have been shown to decrease the risk of atheroma formation by reducing platelet aggregation, endothelial damage, and foam cell formation in animals. Additionally, policosanols have been shown to lower total and low-density lipoprotein (LDL) cholesterol levels by 13 to 23% and 19 to 31%, respectively, while increasing high-density lipoprotein (HDL) cholesterol from 8 to 29%. Policosanols are thought to improve lipid profiles by reducing hepatic cholesterol biosynthesis while enhancing LDL clearance. When compared with statins, policosanols exhibit comparable cholesterol-lowering effects at much smaller doses. The mixture is well tolerated when administered to animals; however, a more precise safety profile is needed for humans. In summary, policosanols are a promising resource in the prevention and therapy of cardiovascular disease (CVD), but these results need to be confirmed in independent laboratories. Key words: policosanols, cardiovascular disease, cholesterol

Epidemiologic data suggest an inverse relationship between the consumption of soy isoflavones and cardiovascular disease risk. The aims of this review are to determine if isoflavones play a role in the hypocholesterolemic effect of soy and whether the studies realized with that scope were adequately designed. In humans, most studies have been performed in postmenopausal women. The results are inconsistent, however; some studies show a decrease in total cholesterol and low-density lipoprotein concentrations, and an increase in high-density lipoprotein levels, and other investigations fail to show any beneficial effect of soy isoflavones on lipid profiles. In most studies, beneficial effects could not be attributed with certainty to soy isoflavones. If these components have any health-protecting effect in humans, it is small in comparison with the effect of soy protein itself. There are currently not enough data to recommend the consumption of isoflavone supplements to lower plasma cholesterol levels. Key words: soy, isoflavones, phytoestrogens, cholesterol, triglycerides, cardiovascular disease risk doi: 10.131/nr.2003.jun.189-203

Two recent reports confirm the role of n-3 polyunsaturated fatty acid (PUFA) consumption in risk reduction for sudden death. The mechanism likely involves an antiarrhythmic effect, further supporting the role of dietary n-3 PUFA in maintenance of human health. Key Words: omega-3, polyunsaturated, fatty acids, sudden death

Research has determined that plant sterol esters are effective in maintaining healthful cholesterol levels. Studies using margarine containing sitostanol-ester and soybean oil sterol-ester showed that both were equally effective in decreasing low-density lipoprotein and blood total cholesterol levels. Neither of the two esters affected high-density lipoprotein cholesterol levels.