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Department of Food Science and Human Nutrition, Colorado State University, Ft. Collins, Colorado
Address reprint requests to: Dr. Christopher L. Melby, Department of Food Science and Human Nutrition, 226 Gifford Building, Colorado State University, Ft. Collins, CO 80523
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSACKNOWLEDGMENTSREFERENCES |
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Methods: Anthropometric characteristics, dietary intake, blood pressure, serum lipids, glucose and insulin, as well as plasma ascorbic acid and vitamin E concentrations, were measured in two groups of Hispanic study participants residing in Denver, Colorado: 74 SDA study participants (x age: 42±1.5 y) and 45 Catholic participants (x age: 44±2.2 y).
Results: The SDAs reported lower dietary intakes of total fat, saturated fat and cholesterol and higher relative intakes of carbohydrate and dietary fiber compared to their Catholic counterparts. The SDAs exhibited significantly lower body mass index (BMI=27.2±0.6) and waist-to-hip ratios (WHR=0.84±0.01) compared to the Catholics (BMI=31.4±1.1; WHR=0.88±0.01). The SDAs, compared to the Catholics, had lower fasting insulin (11.4±0.6 vs. 18.9±3.1 µu/ml) and glucose concentrations (88.6±1.1 vs 104.1±5.4 mg/dl). The SDA Hispanics, compared to the Catholic Hispanics, exhibited significantly lower values for systolic blood pressure (SBP=110±2 vs 118±3 mm Hg), serum total cholesterol (STC=198±5 vs 214±6 mg/dl) and serum triglycerides (TG=152±12 vs 232±27) and higher serum concentrations of high-density lipoprotein cholesterol (HDL-C=44.7±1.3 vs 39.1±1.4 mg/dl) and ascorbic acid (1.14±0.08 vs 0.87±0.07 mg/dl). Low-density lipoprotein cholesterol (LDL-C) and vitamin E concentrations were not significantly different between groups, but the SDAs exhibited lower ratios of STC/HDL-C and LDL-C/HDL-C.
Conclusion: Hispanic American SDAs, who eat a plant-based diet, exhibit a more favorable blood lipid profile, lower blood pressure and lower risk for Type 2 diabetes compared to Hispanic American Catholics, who do not eat a plant-based diet.
Key words: blood pressure, blood lipids, diet, heart disease
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSACKNOWLEDGMENTSREFERENCES |
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Cardiovascular disease risk factors are also present among Hispanic Americans. The San Antonio Heart Study [8] reported significantly higher serum triglyceride and total cholesterol levels among Mexican Americans than among non-Hispanic whites. The Stanford Five-City Project [3] reported significantly lower high-density lipoprotein cholesterol (HDL-C) among Hispanic adults than among non-Hispanic whites. Although hypertension is often linked to obesity, which is frequent among Hispanic Americans, this population appears to have similar or lower blood pressure when compared to non-Hispanic whites [1,9,10]. National data indicate that Mexican Americans have the lowest systolic and diastolic blood pressures when compared to other ethnic groups [11].
Habitual diet appears to play an important role in the prevention of cardiovascular disease and Type 2 diabetes. Epidemiologic research has suggested that a vegetarian diet may decrease some of the risk factors associated with both cardiovascular disease and Type 2 diabetes [12–14], possibly resulting from its lower saturated-fat content and higher amounts of dietary fiber, polyunsaturated fatty acids relative to saturated fatty acids, and micronutrients including ascorbic acid and vitamin E. Recently, the term "semi-vegetarian" has been used to describe individuals who eat a plant-based diet, but who do not entirely abstain from flesh food (consuming it no more than once or twice per week), but who still may exhibit lower risk for CVD and diabetes based on the liberal amounts of grains, legumes, fruits and vegetables present in their diet in contrast to amounts found in the more common omnivorous diet [13]. Studies of African-American SDAs have suggested that such a diet is associated with a more favorable CVD risk factor profile than an omnivorous diet [13]. Few studies have addressed the possibility that such a plant-based diet may provide some protection against CVD and type 2 diabetes in Hispanic Americans.
The purpose of this study was to compare specific risk factors for CVD and type 2 diabetes in Hispanic Seventh Day Adventists with those in Hispanic Catholic omnivores. Dietary micronutrient composition, body composition, blood lipids, glucose, insulin, serum vitamin E and plasma ascorbic acid concentration were investigated.
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METHODS |
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Dietary Intake
Food frequency questionnaires (Right Byte, N-Squared Computing, Silverton, OR) were completed by the subjects to estimate their usual consumption of 141 different foods during the previous three months. The food frequency questionnaires were analyzed for macro- and micro-nutrients. The computer software uses the nutrient data base of the U S Department of Agriculture [15]. We attempted to measure the amount of supplemental nutrients, especially vitamin C and vitamin E taken by the study subjects. However, supplement use was sporadic, and most subjects taking supplements were unable to recall the amounts of vitamins C and E provided from supplemental use; thus, the nutrient intake data do not include supplemental intake.
Blood Pressure
Following a five-minute seated rest, two resting blood pressure measurements were taken using a random-zero mercury sphygmomanometer (Hawksley and Sons, Ltd, London, UK). All measurements were performed on the left arm. The appropriate cuff size was used for all subjects, so that the width of the bladder was 
40% of the arm circumference and the length of the bladder was 80% of the arm circumference. The air was bled from the bladder at a rate which produced a 2 to 3 mm Hg decrease in pressure per second. The first and fifth phase Korotkoff sounds were recorded as systolic blood pressure (SBP) and diastolic blood pressure (DBP). If individuals exhibited bradycardia, the cuff was deflated at a rate of 2 to 3 mm Hg per heart beat. The average of the two BP readings was used in analysis of the data.
Anthropometric Measurements
Height was measured to the nearest 0.1 cm without shoes using a standard stadiometer. Body weight was measured to the nearest 0.1 kg using a standard balance beam scale. Weight included light indoor clothing without shoes. Body Mass Index (BMI) was calculated as weight (kg)/height (m)2. The triceps skinfold thickness was measured to the nearest 1.0 mm on the dominant arm using a Lange (Cambridge, MA) skinfold caliper. Waist, hip and thigh circumference were measured to the nearest 0.5 cm using a non-stretchable measuring tape. Waist circumference was measured at a point estimated to be midway between the xyphoid process of the sternum and the umbilicus in women and at the umbilicus of men. Hip circumference was measured at the widest hip girth. Thigh circumference was measured at the largest horizontal circumference of the upper thigh inferior to the symphysis pubis. The waist-to-hip ratio (WHR) and waist-to-thigh ratio (WTR) were calculated as estimates of the magnitude of central fat patterning.
Blood Assays
Venous blood samples were drawn after a twelve-hour fast from the forearm into a serum separator vacutainer tube. Blood was allowed to clot, centrifuged at 2300 rpm for 20 minutes and placed on ice. Serum was used for analysis of total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides and glucose, using automated spectrophometric procedures (Corning Clinical Laboratory, Denver, CO).
Blood was drawn into a separate tube for plasma ascorbic acid (AA) measurement. The sample was centrifuged and stored on wet ice. Within three hours of data collection, the samples were treated with a 5% trichloroacetic acid (TCA) solution to remove the protein. The samples were frozen at -70° Celsius for a maximum of five days. The assay used for determination of ascorbic acid concentrations was that of Zannoni [16], which relies on the reduction of ferric iron by ascorbic acid. The sample concentrations were read using a spectrophotometer (Beckman, Fullerton, CA).
Blood samples for Vitamin E analysis were centrifuged, placed on ice and frozen at -70° Celsius. The serum vitamin E levels were determined by high-performance liquid chromatography with detection at 300 nm using a modification of the dual wavelength method of Biesalski et al. [17].
Serum insulin concentrations were analyzed by radioimmunoassay (U.S. Pharmacia Company, Kalamazoo, MI).
Statistical Analysis
All data analyses were performed using the Statistical Package for the Social Sciences (SPSS) [18]. Descriptive statistics were computed to determine mean values by group and gender, and a two by two ANOVA (religious group by gender) was used to examine the main effects of group and gender and any interactions. Among the dependent variables of blood pressure, blood lipids, insulin and glucose, gender differences appeared only in HDL-C and diastolic blood pressure. Because of an absence of gender difference in almost all the variables studied, the small number of subjects within each of the four cells when group differences were examined by gender and similar gender distributions for both religious groups, we included males and females together when examining group differences among the dependent variables, but adjusted these values for gender using analysis of covariance. Group values are reported as mean±SEM (standard error of the mean). Analysis of covariance (ANCOVA) was also used to examine group differences in blood pressure, triglycerides and cardiovascular risk ratios (total cholesterol/HDL-C and LDL-C/HDL-C), after adjustment for other variates including BMI and WHR. Partial correlation coefficients, controlling for gender, were calculated to determine the relationships among ascorbic acid, vitamin E, glucose, insulin, blood pressure, blood lipids and anthropometric measurements. Forward-stepwise multiple-regression analyses were used to identify models of the best predictors of blood concentrations of glucose, insulin, lipids and lipid ratios and blood pressure.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSACKNOWLEDGMENTSREFERENCES |
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Non-Dietary Health-Related Behaviors
Based on self-reported questionnaire data, we compared the two groups on several non-dietary health habits that could affect risk factors for cardiovascular disease and diabetes. None of the SDAs reported any consumption of beverage alcohol or use of tobacco, while 42% of the Catholics reported consumption of alcohol and 9.5% were current smokers. Among the Catholics who consumed alcoholic beverages, the mean contribution of beverage alcohol kcal to total energy intake was 2.7% (range 1–8%) according to data from the food-frequency questionnaire. The average self-reported participation in vigorous exercise lasting at least 20 minutes a session was not significantly different between the groups (1.8 times a week for the SDAs and 2.0 times a week for the Catholics).
Food Intake Data
The differences between the religious groups in food intake reflect the emphasis in the SDA church on consumption of a more vegetarian-like diet than an omnivorous diet. The SDAs consumed significantly less flesh food (meat, poultry, fish) than the Catholics (p<0.0001), with a mean of 1.0±0.2 servings (three ounces a serving) a day, compared to a mean consumption of 3.0±0.2 servings a day for the Catholics. Fifty-five percent of the SDAs reported consumption of fewer than seven servings of flesh food a week (i.e. less than daily consumption), compared to only 2% of the Catholics. The average daily consumption of fruits and vegetables was higher among the SDAs than the Catholics (fruits—SDAs: 3.6±0.2 servings/d, Catholics: 2.3±0.2 servings/d, p<0.001; vegetables—SDAs: 3.1±0.4 servings/d, Catholics: 2.0±0.2 servings/d, p<0.02). There was no statistically significant group difference in grain consumption (SDAs: 8.3±0.5 servings/d; Catholics 7.6±0.5 servings/d).
Food Frequency Data (Macro-Nutrients and Micro-Nutrients)
The nutrient intake data, based on a self-reported food-frequency questionnaire, is shown in Table 2 (macronutrients) and Table 3 (micronutrients). There was no significant difference between SDAs and Catholics for total calorie intake. Macronutrient intake data were as expected: because of their greater consumption of fruits and vegetables, the SDAs exhibited higher relative intakes of carbohydrates and dietary fiber and lower absolute and relative intakes of protein, total fat and saturated fat. The groups did not differ in the amount of polyunsaturated fatty acids consumed. The SDAs ingested significantly less dietary cholesterol (191±24 mg) than the Catholics (307±31 mg).
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Insulin, Glucose, Blood Pressure, Lipids and Antioxidants
The group mean values for fasting serum glucose and insulin concentrations, adjusted for age and gender, appear in Table 4. The SDAs had significantly lower insulin and glucose concentrations. Only 1% of SDAs had fasting plasma glucose 120 mg/dl, while 13% of Catholics did. Additionally, fasting insulin concentrations 20 µu/ml were found in only 7.5% of SDAs, but in 29.5% of omnivores (data not in table form).
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Adjusted Blood Pressure, Triglycerides and Cholesterol Ratios
Table 5 contains adjusted mean values for blood pressure, triglycerides and cholesterol ratios after inclusion of variates, such as BMI, WHR and plasma insulin concentration in the model, as well as age and gender. The values were adjusted for variables that were correlated with these measures, were different between groups and had a physiological basis for explaining at least some of the group differences in the dependent variables. Statistically significant group differences in a number of risk factors disappeared or were attenuated by adjustment of the means for measures of BMI, waist circumference, and/or waist/hip ratio. Specifically, after adjustment for waist circumference, the group differences for systolic blood pressure were no longer significant. The LDL-C/HDL-C risk ratio was no longer significant after adjustment for waist/hip ratio. However, the serum triglyceride concentration and the STC/HDL-C remained significantly lower in the SDAs even after adjustment for waist circumference and for waist/hip ratio, respectively.
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Multiple Regression Analysis for Blood Pressure
Table 7 contains the multiple regression models for SBP and DBP. The variables waist circumference, age and glucose together explained 45% of the variability in SBP for the entire sample. Waist circumference explained most of the variability, followed by age and glucose as independent predictors. For the DBP model, waist circumference, insulin and age accounted for 25% of the variability in the sample. As with SBP, waist circumference was the greatest independent contributor, explaining 14% of the variability.
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DISCUSSION |
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Nutrient Intakes
As expected, based on the higher intakes of fruits and vegetables and the lower intake of flesh food in the SDA group, its members’ intakes of total fat intake, saturated fat intake and dietary cholesterol were lower and intake of dietary fiber higher than those of the Catholics. These dietary differences may contribute to the lower levels of cardiovascular disease risk in the SDAs. While we found no strong correlations between dietary variables and specific risk factors, this is not surprising given the cross-sectional nature of the study, the small sample size and the known difficulties in accurately quantifying nutrient intake. Despite the fact that the SDAs reported a mean energy intake that was 300 kcal/d lower than that of the Catholics, these differences did not reach statistical significance owing to the large variability reported in energy intake. However, one cannot rule out the possibility that a lower energy intake among the SDAs contributes to their lower body weights and lower estimates of fat patterning, which in turn contribute to lower risk for both cardiovascular disease and diabetes. Obviously, a lower energy intake, greater energy expenditure or both, in comparison to the Catholics’, must explain the lower body mass index of the SDAs. There were no group differences in reported levels of occupational activity or in the frequency of leisure-time exercise performed for at least 20 min a session.
Blood Lipids and Blood Pressure
We found significantly lower systolic blood pressure, serum total cholesterol and triglycerides in Hispanic SDAs than in Hispanic Catholics. This blood pressure difference disappeared after adjustment for waist circumference, indicating that the group differences in fat patterning were an important contributor to the blood pressure differences. This conclusion is further supported by the finding that, among the entire sample, the waist circumference measure was the best individual predictor of SBP in the multiple regression analysis. Note, that the mean systolic blood pressure was within recommended guidelines for both groups. These data are congruent with those of other studies which have found low rates of hypertension in Hispanic adults, despite the presence of significant risk factors for hypertension, including elevated BMI and waist:hip ratio, high fasting plasma-insulin concentrations and other characteristics of syndrome X [1–3,9].
We did not exclude those individuals on antihypertensive medication from the study for the following reason. Previous research has suggested that SDAs have a lower prevalence of hypertension than nonSDAs. To limit the study to only normotensive individuals would have potentially resulted in selection bias due to a disproportionately greater rate of exclusion of higher-risk individuals from the Catholic group than from the SDAs. That is, potentially more Catholics would have been excluded because of their higher prevalence of HT compared to that of the SDAs, thus diluting any true differences in characteristics related to blood pressure such as BMI, waist-to-hip ratio, plasma insulin, plasma lipids, and so on. On the other hand, in regard to blood pressure in the present study, it is likely that larger blood pressure differences would have existed between groups had not a higher percentage of Catholic subjects (16% vs. 6%) used drug therapy to lower their blood pressures by pharmacologic means. Nevertheless, we did analyze the data after excluding those individuals on antihypertensive medication from both groups and found that group differences in risk factors for diabetes and cardiovascular disease remained statistically significant.
The lower serum total cholesterol and triglyceride concentrations, combined with higher HDL-C, indicate a greater risk for cardiovascular disease among the Catholic omnivores. As is true for blood pressure, the more favorable lipid profile of the SDAs is partly explained by their lower waist circumference and waist-to-hip ratio compared to the Catholics. Interestingly, despite their higher energy-intake percent from carbohydrates (higher intakes of fruits and vegetables), the SDAs exhibited lower serum triglyceride and higher HDL-C concentrations than the Catholics. These results are interesting given that previous research has found that high carbohydrate diets cause hypertriglyceridemia and decrease HDL-C concentrations [19]. Possibly, liberal consumption of carbohydrate and dietary fibers via fruits and vegetables, in the face of low saturated fat intake, has a favorable rather than detrimental effect on the blood lipid profile. The lower values for body mass index, estimates of central fat patterning (waist circumference and WHR) and basal plasma insulin concentrations of the SDAs appear to favor their lower serum triglyceride and higher HDL-C concentrations, even given their higher carbohydrate intake.
Insulin and Glucose
The lower fasting insulin and glucose concentrations of the SDAs suggests higher insulin sensitivity than found in the Catholics. Hyperinsulinemia has been reported to be an independent marker for risk of developing coronary heart disease [20,21] and is related to the development of Type 2 diabetes [20] and hypertension [5,22,23]. In the present study, the fasting plasma-insulin values were significantly positively correlated with other well-known aspects of the insulin-resistance syndrome, including body mass index, estimates of fat patterning and systolic blood pressure, and inversely correlated with HDL-C concentrations. The lower basal insulin concentrations of SDAs suggests better insulin sensitivity, a circumstance which likely contributes to their lower systolic blood pressure and more favorable lipid profiles.
Ascorbic Acid and Vitamin E
Both vitamin C and vitamin E are recognized as important antioxidants that play a role in protecting LDL-C from oxidative modification [24]. Individuals who eat more fruits and vegetables are more likely to have high levels of plasma ascorbic acid. Although the dietary intake of vitamin C estimated from the food frequency questionnaire did not differ between SDAs and Catholics, we found higher plasma AA in SDAs. This is not unusual given that the association between plasma AA concentrations and estimated AA intake is often weak [25]. Smoking is not an explanation for the differences observed between groups for plasma AA, because none of the SDAs reported any tobacco use, and only four Catholics were current smokers. Group differences in plasma AA remained after exclusion of the Catholic smokers. Plasma AA was also directly correlated with HDL-C, as has been previously shown [26]. However, plasma AA was also directly associated with serum total cholesterol and LDL-C; this was unexpected, based on our previous studies of African-Americans [26]. Hallfrisch et al. [27] also found a positive association between plasma AA and LDL-C in women, but did not speculate on the cause.
Caveats and Limitations
It might be argued that the group differences seen in this study result from sampling bias, such that there was a tendency for healthy Hispanic Seventh-Day Adventists to volunteer for the study, while the Catholics were represented by a disproportionately large percentage of individuals at high risk for chronic disease. Stated another way, unhealthy SDAs and healthy Catholics might have been less prone to participate for some reason. Without a much larger sample, obtained by random selection from the two populations, we cannot discount this possibility. However, we used the identical method in recruiting subjects from their respective churches, and the response burden for study participation was the same for each group. We obtained our samples of Hispanic SDAs, who eat a plant-based diet, and Hispanic Catholic omnivores from the same area of Colorado and from churches which are close to each other in Denver; this minimized confounding due to any group differences in socio-economic status and education. The two groups that we studied were similar in age, years of church membership, education level and estimated levels of occupational physical activity and planned exercise.
An obvious difference between the SDAs and the Catholics which could contribute to at least some of the differences in the dependent variables was alcohol consumption. None of the SDAs reported use of alcohol, while 42% of the Catholics reported using beverage alcohol. We did not attempt to compare group characteristics after statistical adjustment for alcohol consumption. Interpretation of any attempts to adjust statistically the group differences in cardiovascular disease and diabetes risk factors by covarying for differences in alcohol consumption would be suspect, based on the lack of any variability in alcohol consumption in the SDAs.
Another possible confounding variable is the number of years or generations that the Hispanic person has lived in the United States. In our study, the majority of Hispanics from both dietary groups were first generation, and there were no group differences in the distribution of subjects categorized as first and second generation immigrants.
Conclusions
Urban Hispanic-American SDAs were found to exhibit lower dietary intakes of protein and of total and saturated fat and higher relative intakes of carbohydrate and dietary fiber than their Catholic counterparts. They also exhibited a more favorable blood-lipid profile, lower systolic blood pressure and lower risk for Type 2 diabetes than Hispanic omnivores. The lower BMI and estimates of fat patterning, waist circumference and waist/hip ratio of the SDAs contributed to the differences in blood pressure, serum lipids, glucose and insulin. Given the observational nature of this study, it is unclear to what extent these differences are related to diet or to other as yet unexplained factors. Future research should seek to determine whether the plant-based diet of many SDAs is causally or only coincidentally related to lower risk for cardiovascular disease and diabetes in Hispanic adults.
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ACKNOWLEDGMENTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSACKNOWLEDGMENTSREFERENCES |
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Received May 1, 1998. Accepted September 1, 1998.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSACKNOWLEDGMENTSREFERENCES |
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-Tocopherol) in human serum by isocratic absorption HPLC.
Int J Vitam Nutr Res
56:
319–327,
1986.[Medline]
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