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Open Access Publications from the University of California


Effects of Walnuts on Serum Cholesterol Levels in People with Normo- or Hyperlipidemia

Hyperlipidemia, particularly in the form of elevated low-density lipoprotein (LDL) levels, is a major risk factor for coronary heart disease (3). A diet low in saturated fatty acids (SFAs) and higher in monounsaturated and polyunsaturated fatty acids (MUFAs and PUFAs) has been shown to exert beneficial effects on serum lipid profiles. Walnuts are particularly rich in PUFAs such as linoleic acid and α-linolenic acid and thus may help improve serum lipid levels. Recent studies have been conducted to examine effects of walnut consumption on serum lipids in normocholesterolemic and in hyperlipidemic people. Studies of both groups reveal that walnuts tend to improve serum lipid profiles by reducing LDL and total cholesterol levels (5-11). The studies conclude that walnut consumption may help reduce risk of heart disease. As this is a relatively young field of research, more studies using larger sample sizes and clearer standards for accurately attributing properties to walnuts should be conducted to provide a better understanding of the role of walnuts in potentially lowering one’s risk of heart disease.

Golden Rice: Genetically Modified to Reduce Vitamin A Deficiency, Benefit or Hazard?

The quantity of genetically modified (GM) foods has been consistently increasing while public concern grows. GM foods have been designed to be resistant to herbicides and high salinity, increase yields, increase esthetic appeal, use as vaccines, and increase nutritional value (1). Golden Rice is a GM crop intended to increase dietary vitamin A. A serious health problem in developing countries, vitamin A deficiency can lead to blindness and premature death. Rice, a food staple produces geranylgeranyl diphosphate (GGPP), an early precursor of beta-carotene. The whole beta-carotene biosynthesis pathway (2 daffodil genes and 1 bacterium gene) was engineered with into rice endosperm to convert the GGPP to beta-carotene. The product, Golden Rice, yields 1.6 – 2.0 μg beta-carotene/g of dry rice (2). Beta-carotene is not toxic and can be stored by body. The body converts beta-carotene into Vitamin A, which is toxic at high levels. Golden Rice has potential to be a valuable asset against global Vitamin A deficiency. No evidence has found GM foods to be hazardous in terms of gene transfer, toxicity, or pathogencity. However, GM foods have found to be allergenic. With appropriate regulation, GM foods have potential to have a positive impact on health.

FROM FISH TO FETUS: Are the Neurotoxic Effects of Methylmercury a Risk of Maternal Fish Consumption?

While environmental pollution has demonstrated the neurotoxic and teratogenic effects of methylmercury, the risk of damaging the developing brain by consuming fish that naturally contain a much smaller mercury concentration is yet to be determined. The current belief and precaution is that for pregnant women and young children, this risk outweighs the many benefits of fish consumption. Landmark studies conducted in the Faroe Islands and the Republic of Seychelles, respectively, have yielded conflicting outcomes in cognitive function in children who have been exposed both pre- and postnatally to methylmercury concentrations more than 10 times that seen in the United States. Faroese children demonstrated some cognitive deficits in language, attention, and memory, while the Seychellois did not manifest any. The confusion may likely be explained by dietary differences, particularly in seafood consumption, as well as differences in genetic endowment. Nevertheless, more cohort, animal, and other investigative studies must be conducted in order to understand not only the mechanism of methylmercury-mediated toxicity in the developing brain, but also the exact risks of maternal fish consumption, for the sake of effective health policy and the mental health of our posterity.

Tomatoes and Prostate Cancer Prevention

Prostate cancer is the second most common cause of male cancer death in the United States (1). The American Cancer Society predicts that in 2003 there will be 220,900 new cases and 28,900 deaths from prostate cancer in the U.S. (12). Although there have been mixed results, the data presented from epidemiologic studies suggests a correlation between lower prostate cancer risk and tomato consumption (2,4,8,6,7). Tomatoes are a source of vitamins A and C, folate, potassium, calcium, iron, and carotenoids (6,7). Of the carotenoids in tomatoes, lycopene is the most abundant and is postulated to work as a chemopreventive agent through antioxidant properties. While there have been studies that do not support this correlation, they have either been done with in populations that consume levels of lycopene, too low to show differences between high and low consumers, or they have not included the most relevant bioavailable sources of lycopene, in processed tomato products. The largest prospective epidemiologic study to date was the Physician’s Health Study conducted in male health professionals from 1986-1998. The data from 47,365 participants showed that the increased consumption of tomatoes and tomato products was associated with increased serum levels of lycopene as well as lower risks for prostate cancer (4,8). Both epidemiologic and the limited clinical data to date, suggest an inverse correlation between increased tomato consumption or serum lycopene levels and decreased risks of prostate cancer (2,7).

The Effect of Phytoestrogens on Hot Flashes

Phytoestrogens are heterophenolic compounds derived from plants that when decongugated in the gastrointestinal tract exhibit estrogenic effects (1). Consequently, food products and tablet form phytoestrogens are being increasingly promoted as natural alternatives to hormone replacement therapy (HRT) in postmenopausal women who are either not eligible or chose not to follow the traditionally prescribed treatment. Such suggestions were coupled to reports that demonstrated that Asian diets rich in phytoestrogens contributed to a decrease in climacteric associated symptoms (8). Although there is some evidence that phytoestrogens are effective in reducing menopausal symptoms, such investigations are still in their infancy (16, 17). More interventional clinical trials are required to determine phytoestrogen efficacy and safety before definitive conclusions can be made. A review of the trials investigating the effect of isolated and dietary phytoestrogen on the frequency and severity of hot flashes is presented, with additional attention to given safety, individual effectiveness considerations, and a comparison of Asian and American diets.

Selenium and Prostate Cancer

Prostate cancer is a prevalent disease, and it is an ideal target for chemoprevention because of its high incidence and long latency. Selenium, a cofactor for an antioxidant, has been shown to increase apoptosis and decrease cell number in prostate cancer cells (10). These effects are surprising because they occur at the level of gene expression, and they appear to be independent to selenium’s role as an antioxidant. Clark’s study in 1996 first proposed the idea of selenium as a chemopreventive element for prostate cancer, and various in vivo and in vitro studies support his findings (7). However, some argue that only patients will low baseline levels of selenium decrease their risk for prostate cancer through selenium. The SELECT study is a 12-year study aimed at elucidating these results, but current research supports the claim that patients with a low baseline level of selenium benefit from supplementation. Selenium obtained from natural dietary sources and multivitamins appears more advantageous at this point because there are questions of an increased risk of prostate cancer related to too much selenium. In spite of this risk, selenium offers an important potential alternative to standard therapy.