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Masthead
Volume 16 - Number 4 Winter 1999


TABLE OF CONTENTS


ENC

COMMON ABBREVIATIONS
BMI: body mass index (kg/m2)
CAD: coronary artery disease
CHD: coronary heart disease
CHO: carbohydrate
CI: confidence interval
CVD: cardiovascular disease
ene: energy
HDL: high density lipoprotein
LDL: low density lipoprotein
Lp(a): lipoprotein (a)
MI: myocardial infarction
MUFA: monounsaturated fatty acids
NCEP: National Cholesterol Education Program
P:S: dietary polyunsaturated:saturated fat ratio
PUFA: polyunsaturated fatty acids
RR: relative risk
SFA: saturated fatty acids
TAG: triacylglycerol
VLDL: very low density lipoprotein


Fruits and Vegetables Protects Against Ischemic Stroke

For the past several years, nutritionists have been promoting the "5-A-Day" campaign to increase fruit and vegetable intake as an intervention to lower CVD and cancer in the population. And findings from a new study by Joshipura et al. strongly supports the role of fruits and vegetables in protecting against chronic illness. Based on the dietary habits of female nurses and male health professionals in the Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS), eating 5 servings a day of fruits and vegetables was associated with a significantly decreased incidence of ischemic stroke.  

In these prospective cohort studies with 75,596 females and 38,683 males, 366 and 204 cases of ischemic stroke were reported in women and men, respectively, during the follow-up period. The median intake of total fruits and vegetables was 5.8 servings per day in women and 5.1 serving per day in men. The prevalence of ischemic stroke was 31% lower in the quintile with the highest fruit and vegetable intakes (9.7 servings) compared with the lowest quintile (2.7 servings). Each serving of fruits and vegetables was associated with a 6% lower risk of ischemic stroke. It was also observed that higher fruit and vegetable intakes were associated with a healthy lifestyle as indicated by higher rates of physical activity and multivitamin supplement intake, and lower rates of smoking. The protective role of fruits and vegetables against ischemic stroke persisted even after controlling for multiple CVD risk confounders.

High intakes of cruciferous vegetable (broccoli and cabbage), green leafy vegetables, citrus fruit juices, and vitamin C-rich fruits and vegetables were especially protective against ischemic stroke. The multivariate RRs of ischemic stroke per 1 serving of cruciferous vegetable was 0.68 (95% CI, 0.49-0.94), green leafy vegetable 0.79 (95% CI, 0.62-0.99), citrus fruit juices 0.75 (95% CI, 0.62-0.99), and vitamin C-rich fruits and vegetables 0.87 (95% CI, 0.61-0.96). However, "analyses of individual fruit and vegetable items that constituted the composite items did not show any single fruit or vegetable that was strikingly more protective than others." Potatoes and legumes did not protect against ischemic stroke, the RR values were 1.21 and 1.09, respectively. 

The benefits associated with fruit and vegetable intake against ischemic stroke were stronger in current smokers and non-supplement users. However, the actual cases of ischemic stroke were still much smaller in supplement users and non-smokers. The strength of this relationship found in smokers and non-supplement uses was probably the result of an attenuated relationship following adjustment for standard CVD risk factors in the vitamin users and non-smokers. Current findings also affirm the 5-A-Day campaign. It showed that eating 5-5.9 servings of fruits and vegetables resulted in maximum benefit. Eating more than this amount did not yield further benefit.

The data from these 2 large epidemiological studies strongly encourage increased fruit and vegetable consumption for ischemic stroke risk reduction. It seems that 5 servings of cruciferous and green leafy vegetables and citrus fruits and juices are especially beneficial in protecting against ischemic stroke.

Joshipura KJ, Ascherio A, Manson JE, et al. Fruit and vegetable intake in relation to risk of ischemic stroke. JAMA. 1999;282:1233-1239.  

Key Messages

  • Fruit and vegetable intake is associated with lower ischemic stroke.
  • People with higher fruit and vegetable intake also had lower CVD risk factors.
  • 5-6 servings of fruits and vegetables were associated with maximum CVD benefit.
  • Cruciferous leafy green vegetables, and citrus fruits and juices were especially protective against ischemic stroke.

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Dietary Fiber Intake Associated with Low Blood Insulin Levels

Previous studies have firmly established a cardioprotective role of dietary fiber in humans. For instance, high fiber consumption is associated with achieving a healthy body weight, blood pressure, blood cholesterol level, and normal blood clotting factors. According to a new study by Ludwig  Ludwig od clotting factors. According to a new study by Ludwig and colleagues, one possible mechanism behind this effect is lower insulin levels following high fiber intake.

In this multi-centered, prospective study with 2,909 young adults between the ages of 18-30 years, the investigators examined the role of fiber consumption and its association with insulin levels, body weight, and other CVD risk factors as related to other dietary components. Based on dietary histories taken during the 7th year of this 10 year study, it was evident that fiber intake was directly associated with positive lifestyle factors such as a higher fitness level and vitamin supplement use, and inversely associated with smoking. Fat intake, on the other hand, was associated with smoking, inactivity, and lower vitamin supplement use. Dietary fiber intake was higher among females and older study participants. Aside from the healthier lifestyle factors, people with higher fiber intakes, also had lower body weights, waist-to-hip ratios, and fasting and 2 hour post-glucose insulin levels compared to the group with the lowest fiber intake. The difference in body weight between the lowest quintile (10 gm) and the highest quintile (25 gm) of dietary fiber was 8.1 lbs in whites and 8.0 lbs in blacks. The mean difference in waist-to-hip ratio, fasting insulin, and 2 hour post-glucose insulin levels for all subjects were  -0.011, -1.1 �U/ml, and -9.9 �U/ml, respectively, between quintiles 1 and 5. Other dietary factors, total fat, saturated and unsaturated fat, and CHO, did not show significant differences in these 2 groups.

In addition to the physical changes noted above, the highest fiber intake was also associated with improved blood pressure and lipid parameters. The systolic blood pressure decreased by 1.2 mm Hg, TAG decreased by 0.6 mg/dl, HDL cholesterol increased by 1.3 mg/dl, LDL cholesterol decreased by 4.3 mg/dl, and fibrinogen decreased by 7.2 mg/dl. These changes were much larger before adjusting for fasting insulin. Dietary fats were not associated with such change in CVD risk factors.

The inverse relationship noted between dietary fiber and body weight, fasting insulin, lipids, and fibrinogen levels in the current study, along with similar findings from the Health Professional's Follow-up Study, lead Ludwig and colleagues to conclude that "fiber may play a greater role in determining CVD risk than total or saturated fat intake." This theory is based on the premise that a high fiber intake results in lower blood insulin levels due to lower glycemic index associated with dietary fiber. Thus, by lowering insulin levels it is possible to alter metabolic mechanisms associated with desire to consume excess food. Also, independent of its effect on insulin, dietary fiber intake has been shown to decrease body weight, in part due to low energy density of these foods resulting in lower insulin resistance as well as other CVD risk factors.        

Ludwig DS, Pereira MA, Kroenke CH, et al. Dietary fiber, weight gain, and cardiovascular risk factors in young adults. JAMA. 1999;282:1539-1546.

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Weight Loss Diet with Daily Fish Intake is Associated with Improved CVD Risk

Weight loss and diet therapy have long been used to counter elevated serum lipids, lipoproteins, and glucose concentrations associated with many chronic maladies such as CHD, diabetes, and hypertension. In a new study by Mori et al., overweight adults achieved reduction in these measurements when these 2 treatment modalities were simultaneously incorporated. In this investigation, the researchers tested the independent and combined effects of weight loss and omega-3 rich fish intake on serum lipids, glucose, and insulin levels in 63 hypertensive subjects. During the 16-week intervention, all subjects concurrently received antihypertensive treatment along with one of the following dietary modifications: weight maintenance diet (control group), weight maintenance diet with daily fish intake (fish group), weight loss diet (weight loss group), and weight loss diet with daily fish intake diet (combined group). Subjects on the 2 fish diets were provided with Greenland turbot, canned sardine, canned tuna, and canned salmon in order to increase omega-3 fatty acid intake by 3.65 gm/day. The baseline clinical and biochemical measurements were similar among the study groups. However, post-treatment concentrations were vastly different. For example, as expected, the cohorts in the 2 weight loss diets lost more weight than the 2 weight maintenance groups. The net difference in mean weight loss was 12 pounds compared to no weight change in the 2 weight maintenance groups. Also, in these groups, the total energy and percent of total fat, SFA, and MUFA intakes were lower. The fish diets were associated with a significantly higher intake of protein and PUFA. The 2 fish diets also resulted in a 5.4% increase in plasma omega-3 fatty acid levels and 2.4% decrease in plasma omega-6 fatty acids. All other macronutrient intakes were similar among the groups.

After treatment, the weight loss diet was associated with a 29% (4.05 pmol/l) reduction in fasting insulin levels and 28% and 8% reductions in the area under the curve (AUC) for insulin and glucose during an oral-glucose-tolerance-test, respectively. The fish diet alone did not result in changes in fasting blood glucose and insulin levels, however, following the combined treatment, these concentrations were significantly lower. For example, the fasting insulin level deceased by 33% (4.28 pmol/l) and ACU for glucose and insulin during the oral-glucose-tolerance-test decreased by 9% (81 mmol/l) and 32% (2,846 mmol/l), respectively, indicating improve glucose metabolism. The effects of weight loss and fish intake combined on the serum lipid and lipoprotein levels were much greater than weight loss or fish intake separately. For example, plasma TAG decreased by 67 gm/dl (38%) compared to -22 mg/dl in the fish group and -20 mg/dl in the weight loss group. Also, the increase in plasma HDL2 cholesterol following combined treatment was significantly higher than with the other 3 test diets. The increases in plasma total cholesterol, LDL cholesterol, and HDL cholesterol levels during the fish diet were not statistically different. Weight loss was associated with a decrease in total cholesterol and increase in HDL and LDL cholesterol concentrations. In addition to improvement in glucose metabolism and serum lipid parameters, this combined therapy was also effective in lowering blood pressure in these hypertensive adults. The systolic and diastolic blood pressures decreased by 13 and 9.3 mm Hg, respectively. This was approximately two times more than the changes noted following the fish and weight loss diets separately. 

The data from the study by Mori et al. indicate that adding fish to a low caloric diet is an effective way to control blood glucose, insulin and lipid metabolism as well as blood pressure. Even though dietary omega-3 fatty acids are associated with increase in glycemia, secondary to hepatic glucose production and diminished insulin secretion, combining it with a weight loss diet can lead to a synergistic effect on lowering blood glucose concentrations. Finally, omega-3 fatty acid intake along with a reduced calorie diet might be a safe treatment for high blood pressure without the negative side-effects associated with some anti-hypertension drugs. 

Mori TA, Bao DQ, Burke V, et al. Dietary fish as a major component of a weight-loss diet: effect on serum lipids, glucose, and insulin metabolism in overweight hypertensive subjects. Am J Clin Nutr. 1999;70:817-825.

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Purple Grape Juice Lowers LDL Oxidation and Improves Endothelial Function

In the family of grape products, purple grape juice has been overshadowed by cardioprotective roles of red wine. However, the tide is beginning to turn. According to Stein et al., like red wine, flavonoids found in purple grape juice improve endothelial function and lower LDL oxidation rates, independent of alcohol.

In this 2-week clinical trial, 15 adults with a history of CHD consumed 8 ml of purple grape juice per kg of  body weight, daily. All other fruit products, tea, and alcoholic beverage consumption were prohibited. However, no changes were recommended regarding the subjects' lipid lowering medication and dietary supplemental practices.

The effects of purple grape juice on the flow-mediated vasodilation (FMD) were measured using high-resolution brachial artery ultrasonography. Baseline FMD measurement revealed that subjects had impaired initial FMD values (2.2 � 2.9%) which increased to 6.4 � 4.7% after 2 weeks of purple grape juice consumption. The susceptibility of LDL to oxidation was also improved following grape juice consumption which increased the lag time of conjugated diene formation by 34.5% (87 � 29 min to 117 � 23 min). These CVD protective effects were seen in spite of an increase in plasma total cholesterol, LDL cholesterol, HDL cholesterol, TAG, total cholesterol/HDL cholesterol ratio, and insulin levels following grape juice intake.

The results from this investigation show that drinking purple grape juice is associated with improved endothelial function as well as reduced LDL oxidation. These cardioprotective effects were evident in spite of subjects' lipid lowering and antioxidant supplement use. Also, the fact that this relationship was evident in the presence of increased plasma lipids suggests that grape juice could be a relatively strong protective factor tool against CVD. The authors concluded that "improved endothelium-dependent vasodilation and prevention of LDL oxidation are potential mechanisms by which flavonoids in purple grape products may prevent cardiovascular events, independent of alcohol content."

Stein JH, Keevil JG, Wiebe DA. et al. Purple grape juice improves endothelial function and reduces the susceptibility of LDL cholesterol to oxidation in patients with coronary artery disease. Circulation. 1999;100:1050-1055.  

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Alcoholic Beverage Lowers CHD Risk

The findings from Wannamethee and Shaper's investigation add further evidence to a growing body of knowledge that regular alcohol intake is associated with lower CHD risk. In this prospective study, researchers compared the drinking habits of 7,272 middle-aged men in the British Regional Heart Study with CHD events and all-cause mortality rates during a 16.8 years follow-up period. During the initial screening, the subjects' daily alcohol habits (frequency, quantity, and type of alcoholic beverage) as well as other lifestyle behaviors and medical history were recorded by a research nurse. Based on this information, subjects were classified into 5 different alcohol intake groups: none, occasional (less than 1 drink per week), light (1-15 drinks per week), moderate (16-42 drinks per week), and heavy (more than 6 drinks per day). There were 901 cases of CHD events, 456 nonfatal and 445 fatal; and 1308 deaths from all-causes, 595 cardiovascular and 713 noncardiovascular.

These data indicated a U-shaped relationship between alcohol intake and age adjusted major CHD events and all-cause mortality, with the lowest rates seen in light drinkers. However, when other CHD risk factors were included in the analysis, the RR for CHD events and all-cause mortality was not different among the light, moderate, and heavy drinkers. The researchers combined the data into 1 collective group termed regular drinkers and compared this group to occasional alcohol drinkers. The regular drinkers had a 23% lower risk of CHD events; however, this advantage was not observed with all-cause mortality. Type of alcoholic beverages consumed by the study cohorts was a factor in the observed outcome. For example, the lower CHD risk was observed only in men who regularly drank beer, spirits, or beer and spirits. In the case of all-cause death, type of alcohol beverage consumed did not alter the relationship. This unexpected outcome might be due to a lower age-adjusted absolute rate of both CHD events and all-cause mortality. However, when the effects of different types of alcoholic beverages on CHD events and all-cause mortality were separated, wine consumption was associated with lower risk compared to both beer and spirits. One possible explanation for lower CHD events and all-cause mortality in wind drinkers is that as a group, they had a much healthier lifestyle and were in better physical health.

This study shows that enjoying a moderate amount of alcohol can be beneficial to the heart, but does not protect against all-cause mortality. Wine consumption was slightly better at decreasing CHD risk than beer and spirit.

Wannamethee SG, Shaper AG. Type of alcoholic drink and risk of major coronary heart disease events and all-cause mortality. Am J Public Health. 1999;89:685-690.

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Dietary Olive Oil and LDL Oxidation

Ever since people became  olive oil consumption has dramatically increased in the USA. But according to Ramirez-Tortohealth conscious about their diets, olive oil consumption has dramatically increased in the USA. But according to Ramirez-Tortosa et al., not all olive oils are created equal. It seems that extra-virgin olive oils, which undergo less processing than refined olive oil, contain more alpha-tocopherol and phenolic compounds, and are more protective against CVD. The investigators tested this theory in 24 older, Spanish men with peripheral vascular disease. In this crossover study, subjects replaced visible saturated fat with either extra-virgin olive oil or refined olive oil for a 3 month period each. There was a 3-month washout period in between the dietary trials. Dietary composition between the extra-virgin olive oil diet phase and the refined olive oil diet phase were similar expect for alpha-tocopherol intake. Extra virgin olive oil contained higher alpha-tocopherol levels than refined olive oil. Also, the unsaponifiable matter in extra virgin olive oil had higher concentrations of alpha-tocopherol and polyphenols, while the fatty acid composition was similar between the 2 olive oils. Plasma TAG levels were higher following the extra virgin olive oil diet whereas all other plasma lipid and lipoprotein levels were similar between the 2 diets. The susceptibility of LDL to oxidize was less during the extra virgin olive oil phase. Also, macrophage uptake of oxidized LDL was greater for LDL obtained during the refined olive oil diet phase. While this study did not show an improvement in plasma lipids and lipoproteins following either type of olive oil intake, the reduced LDL oxidation susceptibility with extra virgin olive oil indicates potential benefit in people with a high risk of CVD. It is thought that extra virgin olive oil reduces LDL oxidation due to its high content of polyphenolic antioxidants.

Ramirez-Tortosa MC, Urbano G, Lopez-Jurado M, et al. Extra-virgin olive oil increases the resistance of LDL to oxidation more than refined olive oil in free-living men with peripheral vascular disease. J Nutr. 1999;129:2177-2183

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Black Tea Consumption Lowers Atherosclerosis Risk

In for this intercorrelation using multiple regression analysis the mist of conflicting outcomes, the latest tea study shows an inverse relationship between black tea intake and aortic atherosclerosis in adults over 55 years old. Based on data from the Rotterdam Study of 3,454 Dutch subjects, drinking black tea was associated with less calcification of the aorta. Eighty-four percent of men and 91% of women in the study drank approximately 3 cups and 3.5 cups of tea per day, respectively. And compared to non-tea drinkers in the study, tea drinkers were leaner, and less likely to smoke, drink alcohol and coffee, and eat fatty foods. The tea drinkers were also more likely to take antioxidant supplements and have a higher education level. The change in atherosclerosis progression in the abdominal aorta from baseline to follow-up (2-3 years) was measured using lateral radiographic films. The abdominal aorta calcification was present in 1,900 cases and was classified in three groups: 641 mild (<1 cm), 1,061 moderate (1-5 cm), and 198 severe (>5 cm). No calcification was found in 1,554 subjects who drank 2.9 cups/day of tea compared with 2.4 cups/day of tea in the group with severe calcification. Based on multivariate, logistic regression analyses, tea consumption was associated with lower atherosclerosis risk in only the severe atherosclerosis group. No significant relationship was found in the mild and moderate atherosclerosis groups, after adjusting for confounding variables. The odds ratios across categories of tea intake in the severe atherosclerosis group were 0.54, 0.47, and 0.31 for 1-2 cups, 3-4 cups, and greater than 4 cups, respectively. This association was especially strong in women with severe atherosclerosis. The age-adjusted odds ratio for severe atherosclerosis was 0.23 in the highest tea drinkers. Findings from this study indicate that drinking a nice hot cup of black tea is not only relaxing, but it may also protect the heart due to antioxidant effects of flavonoids found in the tea. Finally, Geleijnse et al. speculated that their outcome was different from the Caerphilly Study in Welsh subjects possibly due to the fact that Welsh subjects added milk to their tea. The added milk was thought to reduce the bioavailability of flavonoids.

Hertog MG, Sweetnam PM, Fehily AM, et al. Antioxidant flavonols and ischemic heart disease in a Welsh population of men: the Caerphilly Study. Am J Clin Nutr. 1997;65: 1489-1494.

Geleijnse JM, Launer LJ, Hofman A, et al. Tea flavonoids may protect against atherosclerosis. Arch Intern Med. 1999;159: 2170-2174.

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The 1999 American Heart Association Annual Meeting Abstract Reviews

The following briefs cover some of the many abstracts presented at the 72th Scientific Sessions of the American Heart Association (AHA) held in Atlanta, Georgia this past November. Abstracts are published in Circulation, AHA's bimonthly journal.

Eggs, Insulin Resistance and Obesity. To determine if differences in the plasma cholesterol response to dietary cholesterol were related to insulin sensitivity, Knopp et al. studied the effects on plasma lipoproteins of adding 2 or 4 eggs per day to the diets of lean insulin-sensitive (LIS n=65), lean insulin-resistant (LIR n=75) and obese insulin-resistant (OIR n=58) subjects. Plasma LDL cholesterol was not significantly increased in any group with 2 eggs/day but was increased in the lean groups with 4 eggs/day. The OIR did not change. Changes in plasma HDL cholesterol mimicked changes in LDL cholesterol and the LDL:HDL ratio was unchanged with either level of egg feeding. Insulin sensitivity was not a factor in the plasma cholesterol response to dietary cholesterol whereas obesity attenuated the observed increases in LDL and HDL cholesterol levels during the 4 eggs/day feeding phase. Knopp et al. Effects of insulin resistance and obesity on the LDL response to egg ingestion. Circulation. 1999;100 (suppl 1):I-116.

Xanthophylls and CHD Risk. Genetic polymorphisms of HDL associated human serum paroxonase (PON) were tested to determine potential effects on CHD risk. The authors investigated gene-diet interactions between PON and xanthophylls, another HDL associated antioxidants. The study population consisted of 375 cases of MI and 273 matched controls. The authors observed no significant differences in dietary carotenoid intakes between PON 1 and PON2 genotypes but adipose levels were significantly different for the genotypes (lutein and zeaxanthin only). Surprisingly, the investigators found that adipose tissue levels of lutein-zeaxanthin was positively associated with significantly lower incidences of MI in both PON1 and PON2 genotypes. This relationship was not found for adipose tissue levels of lycopene and alpha-carotene. The higher levels of lutein-zeaxanthin in the PON2 group suggests differences in xanthophyll metabolism in this group. The data also suggest potential benefits from increased intakes of lutein and zeaxanthin in lowering the risk of MI. Sen et al. Gene-diet interaction between the paraoxonase 192 polymorphism and xanthophylls. Circulation. 1999;100 (suppl 1):I-659.

Cholesterol Absorption, Insulin Resistance and Obesity. Obesity is associated with higher rates of endogenous cholesterol synthesis which can result in lower fractional absorption rates of cholesterol. In this study of 16 obese type 2 diabetic subjects (BMI 32) and 11 normoglycemic obese controls, the investigators found a lower absorption of cholesterol in the diabetics (30%) compared to controls (42%). They also reported that obese diabetic subjects had higher rates of cholesterol synthesis as well as higher rates of fecal bile acid and neutral steroid excretion. The authors concluded that diabetes has a marked influence on cholesterol absorption efficiency, and low cholesterol absorption is part of the insulin resistance syndrome. Simonen et al. Insulin resistance contributes to lowering cholesterol absorption efficiency in obesity. Circulation. 1999;100 (suppl 1):I-116.

Vitamins E and C and Carotid Atherosclerosis. The Antioxidant Supplement in Atherosclerosis Prevention  (ASAP) Study tests the efficacy of vitamin E and C supplementation on the progression of carotid atherosclerosis in 520 smoking and non-smoking men and postmenopausal women aged 45-69 years with hypercholesterolemia. Subjects received either 200 mg/day d-alpha-tocopherol, 500 mg slow-release vitamin C, both vitamins, or placebo for 3 years. The average increases in carotid intima-media thickness were: 0.020 mm/yr in men on placebo, 0.018 vit E, 0.017 vit C, and 0.011 in vit E+C. In women the values were 0.016, 0.015, 0.017 and 0.016mm/yr respectively. The protective effect of the double vitamin intake was greatest in smoking men and absent in women. The data suggest that reasonable doses of both vitamin E and vitamin C can retard the progression of common carotid atherosclerosis especially in regularly smoking hypercholesterolemic men. Salonen et al. The effect of vitamin E and vitamin C on carotid atherosclerotic progression: The Antioxidant Supplementation in Atherosclerosis Prevention (ASAP) Study. Circulation. 1999;100 (suppl 1):I-238.

CHD Risk During Menopause. The Women's Healthy Lifestyle Project is a lifestyle intervention trial in peri and postmenopausal women followed for 5 years. In this study, 535 women (275 controls and 260 lifestyle interventions) were studied to determine the efficacy of non-pharmacological interventions to minimize the increase in plasma LDL cholesterol and weight associated with peri and postmenopause. The lifestyle intervention included reductions in total fat (25% of calories), saturated fat (7% of calories), dietary cholesterol (100 mg/day), total calories (1300 kcal/day), and exercise (1000-1500 kcal/wk). The increases in LDL cholesterol for control and intervention groups were: postmenopause - 12 vs 3.8 mg/dl; with hormone replacement therapy (HRT) - 2.8 vs 2.1 mg/dl; without HRT 11.6 vs 6.3 mg/dl. While the authors concluded that lifestyle interventions can effectively blunt the rise in plasma LDL associated with menopause, the data indicate that this is primarily true only in women not on HRT. Kuller et al. A randomized clinical trial of risk factor modification in 535 healthy women during menopause. Circulation. 1999;100 (suppl 1):I-522.

Fish Consumption and ApoB Metabolism. Studies have shown that fish consumption lowers CVD risk probably by multiple mechanisms including effects on thrombosis and lipoprotein metabolism. In this study, investigators determined the effects of fish consumption on the rates of production of apoB-48 and apoB-100 in the non-fasting state. A high fish diet was associated with a decreased production rate of apoB-48 and apoB-100 in triglyceride rich lipoproteins (TRL) with change in the fractional catabolic rate (FCR). These changes resulted in a reduced TRL pool size. The high fish diet also lowered the LDL apoB-100 pool size through an increase in the production rate coupled with and increase in the FCR. The authors concluded that a diet high in fish (n-3 fatty acids) blunts the postprandial rise in plasma triacylglycerols due to a decrease in TRL apoB production with little effect on the FCR. Lichtenstein et al. Fish consumption decreases TRL apoB-48 & apoB-100 production rates. Circulation. 1999;100 (suppl 1):I-659.

Dietary Fat and Weight Loss. To determine effects of fat type and amount on CVD risk factors during weight loss, 62 subjects were studied using 3 energy restricted (-35%) test diets for 12 weeks: very low fat (10% ene fat); high SFA (32% ene fat, 17% ene SFA); or low SFA (32% ene fat, 6% SFA).  Plasma LDL was lowest with the very low and low SFA diets; however, the fall in plasma HDL levels was less with both 32% fat diets. All diet groups had similar caloric intakes and comparable weight losses and reductions in waist circumference over the 12 week test period. Comparable changes in the plasma glucose response and fasting plasma insulin levels were noted in all 3 diet groups. The fall in blood pressure was least with the low fat diet. The authors concluded that all energy restricted diets improve overall CVD risk factors but that the low SFA diet appeared to confer maximal benefits. Noakes & Clifton. Dietary fats in energy restricted diets: effects on cardiovascular risk factors. Circulation. 1999;100(supp1):I-66

Central Adiposity and Carotid Atherosclerosis. Studies were carried out to determine the associations between overall obesity (BMI) and central adiposity (waist-to-hip ratio, WHR) with the 4 year increase in mean and maximal intima-media thickness (IMT) of the common carotid arteries. The study population involved 774 men 42-60 years of age.  BMI was not associated with the increase in mean and maximal IMT using multiple regression analysis whereas WHR was directly related. Men with WHR of <0.91, 0.91-0.96 and >0.96 had an increase in mean IMT of 0.097, 0.110 and 0.123 mm/4 years. WHR was not associated with the IMT increase in men with LDL cholesterol levels less than 150 mg/dl. The authors concluded that central adiposity accelerates the progression of early atherosclerosis in middle-aged men, especially in those with elevated serum LDL cholesterol. The data would indicate that excess body weight per se is not necessarily a risk factor for carotid atherosclerosis unless associated with central adiposity and an elevated plasma LDL level. Lakka et al. Central obesity and the progression of early carotid atherosclerosis in middle-aged men. Circulation. 1999;100 (suppl 1):I-741.

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Editorial: Epidemiology, Statistics and False Correlations

Over the past years there have been numerous epidemiological surveys showing a null relationship between dietary cholesterol and CVD incidence. These reports appear to contradict many studies published in the 60s and 70s reporting significant relationships between cholesterol in the diet and heart disease. Even today some studies suggest significant relationships between dietary cholesterol and CHD. Why do these various reports from epidemiological surveys appear to be contradictory? The fact is, they really aren't. This apparent conflict can easily by explained by inspection of a report from the Twenty Countries Study by Kromhout et al. (1995). These authors concluded that dietary cholesterol, saturated fat (SFA), and trans-fatty acids were significantly related with CHD incidence as determined by simple correlation. In the case of dietary cholesterol, simple regression analysis indicated a positive correlation between dietary cholesterol and CHD mortality with a r value of 0.55 (P= 0.029). In a similar manner, SFA calories also had a significant relationship of r = 0.88 (P < 0.0001). At first glance it seems that both dietary cholesterol and SFA are positively correlated with CHD rates. The problem is that most cholesterol containing foods are high in SFA (eggs are an exception), and these two nutrients are intercorrelated. In the Twenty Countries Study there was a significant correlation between dietary SFA and cholesterol (r = 0.62, P = 0.011). With multiple regression analysis the only significant dietary correlation is with SFA (P = 0.010) not dietary cholesterol (P = 0.895).

Is dietary cholesterol significantly related to CHD rates in this study population? The answer is yes, and no. Yes, based on simple correlation and no, following correction for the colinearity of SFA and cholesterol in the diet. Kromhout and colleagues stated that: "In the present study, a significant association between average dietary cholesterol intake and long-term mortality rates from coronary heart disease was also found. This correlation was not independent of saturated and trans-fatty acids due to strong intercorrelations.

Clearly, it is easy to document a simple relationship between dietary cholesterol and CHD but such relationships only obscure significant factors such as dietary SFA which do contribute to CHD risk. This becomes clear when it is noted that no studies in the 90s have found a significant relationship between dietary cholesterol and CHD when correcting for this intercorrelation using multiple regression analysis. 

Kromhout D, Menotti A, Bloemberg B, et al. Dietary saturated and trans fatty acids and cholesterol and 25-year mortality from coronary heart disease: the Seven Countries Study. Prev Med. 1995;24:308-15.

Donald J. McNamara, Ph.D.
Executive Editor, Nutrition Close-Up

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Executive Editor: Donald J. McNamara, Ph.D.
Writer/Editor: Linda Min, M.S., R.D.

 

Nutrition Close-Up is published quarterly by the Egg Nutrition Center. Nutrition Close-Up presents up-to-date reviews, summaries and commentaries on the latest research investigating the role of nutrition in health promotion and disease prevention, and the contributions of eggs to a nutritious and healthful diet. Nutrition and health care professionals can receive a FREE subscription for the newsletter by contacting the ENC.

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