TOP NUTRITION NEWSLETTER

VOLUME 2, NO 1:JANUARY 1999

Editorial

This is the first issue of TOP NUTRITION NEWSLETTER in 1999. In this issue, nut consumption and prevention of heart disease,  Strawberries, Spinach, Red Wine or Vitamin C as antioxidants, soluble fiber and cholesterol, and diet and cancer prevention are updated for your interest.

Can nuts prevent heart disease? Clinical trials have shown that dietary supplementation with walnuts or almonds can lead to a decrease in serum cholesterol. This paper uses data from the Nurses Health Study to examine whether nut ingestion over prolonged periods can prevent CHD. The reduction in CHD with high nut consumption is as great as can be expected from treating a patient with a statin. It is good to be able to give patients a positive message in relation to their lifestyle; all too often we seem to be trying to stop them from doing what they enjoy. We can now say that if they eat some nuts with their daily glass of red wine they will probably be substantially reducing their risk of heart disease.

The comparative antioxidant capacity of strawberries, spinach, red wine or vitamin C in the elderly women is the interesting issue in this period.The overall antioxidant capacity in serum or urine of elderly women was significantly increased following the consumption of strawberries, spinach, red wine or vitamin C. The increased serum antioxidant capacity after the treatments of strawberries, spinach, and red wine indicated the possible absorption of phenolic compounds in these diets.

This meta-analysis of 67 controlled trials was the first paper to quantify the cholesterol-lowering effect of major dietary fibers. Independent variables were type and amount of soluble fiber, initial cholesterol concentration, and other important study characteristics. Can various soluble fiber reduce total and LDL cholesterol and how much significant ? Is it a reliable way to reduce total and LDL cholesterol ?

Diet is one of the most important lifestyle factors and has been estimated to account for up to 80% of cancers of the large bowel, breast, and prostate. 2 3 Even lung cancer may have a dietary component, although cigarette smoking is the overwhelming cause of this and contributes also to oropharyngeal, oesophageal, and bladder cancer. Can diet prevent some cancers ?

Hope you enjoyed the holidays and let's have a happy and prosperous new year.

Happy Reading.

Dr Shwe Win

Editor

Can Nuts Prevent Heart Disease?

Reference: BMJ 1998; 317: 1341-5

Summary: It has been suggested that one reason for low mortality rates from coronary heart disease (CHD) in Mediterranean countries is the relatively high consumption of nuts in the local diet. Clinical trials have shown that dietary supplementation with walnuts or almonds can lead to a decrease in serum cholesterol. This paper uses data from the Nurses Health Study to examine whether nut ingestion over prolonged periods can prevent CHD.

In 1976 nearly 122,000 female US nurses aged 30-55 years enrolled in the Nurses Health Study. Baseline data was collected on lifestyle and health. Every two years subjects complete a postal questionnaire on their state of health. The questionnaire includes questions on the development of CHD.

Since 1980 the nurses have also periodically completed detailed dietary questionnaires. Complete and plausible data is available from over 86,000 of the participants. The dietary questionnaire has allowed subjects' consumption of nuts to be recorded. For the purposes of the study one unit of nuts is considered equivalent to 1 oz of nuts or one tablespoon of peanut butter.

The primary study endpoint was incident CHD, defined as non-fatal myocardial infarction or fatal CHD occurring between 1980 and 1994. All such diagnoses were confirmed whenever possible by examination of hospital records or autopsy reports.

The women were divided into four categories based on 1980 baseline frequency of consumption of one unit of nuts: almost never (35%), 1-3 times per month to once per week (51%), 2-4 times per week (9%), five or more times per week (5%). By 1990 nut consumption had decreased so that the proportions in the latter two groups were 4.5% and 3% respectively.

1,255 major CHD events (861 non-fatal and 394 fatal) occurred during the 14 years and 1,133,000 person-years of follow-up. After adjusting for age, smoking and other known risk factors for CHD, the women who ate more than five units of nuts per week at baseline had a relative risk of 0.65 for CHD when compared with women who almost never, or never, ate nuts. The risk reduction was similar for both fatal and non-fatal CHD. The results remained unchanged when adjusted for other recorded dietary variables such as intake of fat, fiber, vegetables, fruit and vitamin supplements. They appeared to apply equally to all identified subgroups (e.g smokers, alcohol users, high body mass index).

The risk with any cohort study, such as this, is that an important confounding variable may have been overlooked. Women who eat a lot of nuts may also have other idiosyncrasies that distinguish them from the others. The authors have adjusted the results as far as possible for all known confounders. The reduction in CHD with high nut consumption is as great as can be expected from treating a patient with a statin. It is good to be able to give patients a positive message in relation to their lifestyle; all too often we seem to be trying to stop them from doing what they enjoy. We can now say that if they eat some nuts with their daily glass of red wine they will probably be substantially reducing their risk of heart disease.

Serum Antioxidant Capacity Is Increased by Consumption of Strawberries, Spinach, Red Wine or Vitamin C in Elderly Women

Reference: J Nutrition 1998; 2383-2390.

It is often assumed that antioxidant nutrients contribute to the protection afforded by fruits, vegetables, and red wine against diseases of aging. However, the effect of fruit, vegetable and red wine consumption on the overall antioxidant status in human is unclear. In this study we investigated the responses in serum total antioxidant capacity following comsumption of strawberries (240 g), spinach (294 g), red wine (300 ml) or vitamin C (1250 mg) in eight elderly women. Total antioxidant capacity was determined using different methods: oxygen radical absorbance capacity (ORAC) assay, Trolox equivalent antioxidant capacity (TEAC) assay and ferric reducing ability (FRAP) assay. The results showed that the total antioxidant capacity of serum determined as ORAC, TEAC and FRAP, using the area under the curve, increased significantly by 7-25% during the 4-h period following consumption of red wine, strawberries, vitamin C or spinach. The total antioxidant capacity of urine determined as ORAC increased (P < 0.05) by 9.6, 27.5, and 44.9% for strawberries, spinach, and vitamin C, respectively, during the 24-h period following these treatments. The plasma vitamin C level after the strawberry drink, and the serum urate level after the strawberry and spinach treatments, also increased significantly. However, the increased vitamin C and urate levels could not fully account for the increased total
antioxidant capacity in serum following the consumption of strawberries, spinach or red wine. We conclude that the consumption of strawberries, spinach or red wine, which are rich in antioxidant phenolic compounds, can increase the serum antioxidant capacity in humans.

The results of this study demonstrated that the consumption of strawberries, spinach, red wine or vitamin C could increase the antioxidant capacity of serum in elderly women. Increases in ORACPCA and FRAP were observed for all these treatments compared to the control. Because serum proteins were removed in the ORACPCA assays and protein produced negligible activity in the FRAP assay, the significant increase of serum antioxidant capacity following these drinks was mainly due to the nonprotein antioxidants in the serum. The increase of total antioxidant capacity of serum after consumption of strawberries, spinach, or vitamin C was further supported by the significant increase of urine ORAC following these treatments.

The increased antioxidant capacity in serum (ORACPCA and FRAP) and urine (ORAC) following the consumption of strawberries or spinach indicated a direct absorption and/or an enhanced production of antioxidants. The absorbed antioxidants included vitamin C, and the produced antioxidants may include uric acid from purine metabolism; plasma vitamin C level was significantly increased after the strawberry drink, and serum urate levels were increased by both the strawberry and spinach treatments. Based on the data from USDA handbooks (USDA 1986), we calculated the strawberry drink contained about 120 mg vitamin C. However, the increased blood vitamin C and urate could be a result of the sparing effect on them by the other antioxidants absorbed from strawberries or spinach. Also, other antioxidants, rather than vitamin C and urate, contributed to half of the increased serum antioxidant capacity. The increased serum ORACPCA AUC and FRAP AUC (1-4 h) after the strawberry drink were 275 and 315 ?mol ? h/L Trolox equivalents, respectively; whereas the increased vitamin C AUC following the strawberry drink during the same time period was only 44 ?mol ? h/L, or 23-44 ?mol ? h/L Trolox equivalents in the ORACPCA assay and 44 ?mol ? h/L Trolox equivalents in the FRAP assay. The antioxidant capacity (Trolox equivalents) of vitamin C was 0.52-1.0 in the ORAC and FRAP assays. Therefore, the contribution of vitamin C to the increased serum ORACPCA and FRAP after the strawberry drink was only 8-14%. Similarly, it was calculated that the contribution of urate to the increased serum ORACPCA and FRAP following the strawberry treatment was 39-42%, and to the increased serum ORACPCA and FRAP following the spinach treatment (1-4 h) was 36-44%.

Significant increases in serum antioxidant capacity were observed in the strawberry and red wine treatments even though total carotenoids decreased. Because of the low plasma carotenoid concentration and the relatively lower antioxidant activity of carotenoids as assessed by the ORAC assay, carotenoids do not make a major contribution to the ORAC in serum.

The other antioxidants responsible for the increased serum antioxidant capacity following the consumption of strawberries or spinach are likely phenolic compounds including flavonoids, although it was not clear which specific phenolic compounds were absorbed. Some phenolic compounds, such as ellagic acid, catechin, rutin, naringin and anthocyanins have been identified in strawberries . It was suggested that phenolic compounds were responsible for the high antioxidant capacity found in strawberries and spinach and also for the differences in the antioxidant capacities between fruits and vegetables.

The absorption of some individual flavonoids in humans was reported by several laboratories. It was reported that in adult women the average plasma concentration of total isoflavones reached 4.4 ?mol/L at 6.5 h after a dose of 2 mg soybean isoflavones/kg body weight. Two studies by Hollman et al. (1995 and 1996) indicate that quercetin glucosides from fried onions were absorbed in humans and that quercetin absorption was enhanced by conjugation with glucose. This was supported by a recent study that suggested quercetin glucosides are capable of interacting with the sodium dependent glucose transport receptors in the mucosal epithelium. The aglycones naringenin and hesperitin were detected by positive chemical ionization-collisionally activated dissociation tandem mass spectrometry (PCI-CAD MS/MS) in human plasma and/or urine after oral administration of naringin and hesperidin. Naringenin was also detected by HPLC/UV either on or in saline-washed erythrocytes 2 and 4 h after the oral administration of naringin.

Red wine contains phenolic compounds, such as quercetin, rutin, catechin and epicatechin; the concentration is about 1 g/L, 20-fold the level found in the average white wine (Singleton 1982). Red wine also has a relatively high ORAC activity of 12.3 mmol/L, which is 5.3-fold the activity measured in white wine (Cao et al. 1995). Red wine, or the phenolic compounds in the red wine, were shown to reduce the susceptibility of human plasma and low-density lipoprotein to lipid peroxidation both in vitro (Frankel et al. 1993) and in vivo (Fuhrman et al. 1995), although the in vivo study has not yet been confirmed . The results of the present study support the antioxidant hypothesis regarding the role of red wine in the `French Paradox' (apparent compatibility of a high fat diet with a low incidence of coronary atherosclerosis); the red wine drink significantly increased the overall antioxidant capacity as reflected in the serum ORACPCA and FRAP.

A single antioxidant, vitamin C, also affected the overall antioxidant status. It appears that strawberries and spinach are as effective in enhancing the overall antioxidant status in serum as a large dose of vitamin C.

In conclusion, the overall antioxidant capacity in serum or urine of elderly women was significantly increased following the consumption of strawberries, spinach, red wine or vitamin C. The increased serum antioxidant capacity after the treatments of strawberries, spinach, and red wine indicated the possible absorption of phenolic compounds in these diets.

Cholesterol-lowering effects of dietary fiber: a meta-analysis

Reference: AJCN 1999;69:30-42.

Background: The effects of dietary soluble fibers on blood cholesterol are uncertain.

Objective: This meta-analysis of 67 controlled trials was performed to quantify the cholesterol-lowering effect of major dietary fibers.

Design: Least-squares regression analyses were used to test the effect on blood lipids of pectin, oat bran, guar gum, and psyllium. Independent variables were type and amount of soluble fiber, initial cholesterol concentration, and other important study characteristics.

Results: Soluble fiber, 2-10 g/d, was associated with small but significant decreases in total cholesterol [-0.045 mmol/ L /g soluble fiber-1 (95% CI: -0.054, -0.035)] and LDL cholesterol [-0.057 mmol /L / g (95% CI: -0.070, -0.044)]. The effects on plasma lipids of soluble fiber from oat, psyllium, or pectin were not significantly different. We were unable to compare effects of guar because of the limited number of studies using 2-10 g/d. Triacylglycerols and HDL cholesterol were not significantly influenced by soluble fiber. Lipid changes were independent of study design, treatment length, and background dietary fat content.

Conclusions: Various soluble fibers reduce total and LDL cholesterol by similar amounts. The effect is small within the practical range of intake. For example, 3 g soluble fiber from oats (3 servings of oatmeal, 28 g each) can decrease total and LDL cholesterol by 0.13 mmol/L. Increasing soluble fiber can make only a small contribution to dietary therapy to lower cholesterol.

Diet and the prevention of cancer

Reference: BMJ 1998;317:1636-1640 ( 12 December )

Cancer is responsible for more deaths annually in the United Kingdom than is ischaemic heart disease. Around half of cancer deaths are due to tumours at four principal sites: lung, bowel, breast, and prostate. These cancers are virtually absent in many countries in the developing world but increase in incidence within one or two generations when migrants move from low to high risk areas.1 Thus many cancers common in Western populations are due to environmental factors, and these cancers should be largely preventable.

Diet is one of the most important lifestyle factors and has been estimated to account for up to 80% of cancers of the large bowel, breast, and prostate. 2 3 Even lung cancer may have a dietary component, although cigarette smoking is the overwhelming cause of this and contributes also to oropharyngeal, oesophageal, and bladder cancer. Physical activity, reproductive and sexual behaviour, infection with hepatitis B and C viruses, infection with helicobacter, and exposure to sunlight, ionising radiation, and environmental chemicals are also important at particular sites. Nevertheless, food and drink has a part to play in many if not all cancers, albeit to a variable extent.

Summary points


Up to 80% of bowel and breast cancer may be preventable by dietary change

Diet contributes to varying extents to the risk of many other cancers, including cancers of the lung, prostate, stomach,
oesophagus, and pancreas

Generally, fruit, vegetables, and fibre have a protective effect, whereas red and processed meat increase the risk of developing
cancer

Other lifestyle factors that increase risk include smoking, alcohol, and overweight

Risk is decreased by physical activity

There is no evidence that vitamin supplements help to prevent cancer