Cardiovascular Health: A Case Study Exploring the Feasibility of a Diet Relatively Rich in Monounsaturated Fats

Cardiovascular disease remains a major health problem in affluent societies. This paper explores whether a low-fat diet rich in monounsaturated fatty acids is a practical proposition for free living young adults. Healthy young Australian adults being trained as health professionals were requested to undertake a computer-assisted analysis of their usual diets and to formulate a modified diet with monounsaturated fatty acids as the major fat source. Subjects also documented their body mass index (BMI) and waist measurement. Sixty-three students provided sufficient information to be included in the analysis. Six females and three males fell outside the optimal BMI range and five females and two males fell into the 'at risk' waist measurement zone. Thirty-three females and 13 males had a relatively high saturated fat intake, and 15 females and 10 ,tales succesfully modified their diet and implemented a diet relatively rich in monounsaturated fat. It is suggested that waist measurement is a predictor of cardiovascular risk and is reputed to be a better index of blood lipids than BMI. A diet rich in monounsaturated fats improves the blood cholesterol profile and one in which monounsaturated fats constitute less than 30% of the total energy derived from fat is a practical recommendation for young adults. This study group did, however, find that such a diet was less convenient and more expensive than a diet rich in saturated fat. This study concludes that selection of a low fat diet which ,layouts monounsaturated fatty acid food sources and personal monitoring of waist measurement are two practical strategies which individuals can readily implement when taking responsibility for promoting their cardiovascular health.

Keywords: monounsaturated fat, cardiovascular disease, diet, waist measurement.

INTRODUCTION

Excess weight is an indicator of increased cardiovascular risk and self-care to avoid cardiovascular disease is an accepted lifestyle option in Western society. Compared to normal-weight persons, overweight individuals have higher total cholesterol and significantly lower high-density lipoprotein (HDL) levels [ 1], and obese individuals of 20-45 years have five or six times the risk of hypertension [ 2]. Overweight populations run an increased risk of hypercholesterolaemia, hypertension and diabetes. The body mass index (BMI) is widely used for assessing body weight in persons aged >/- 20 years [ 3]. BMI is usually interpreted as < 20 kg m-2 being indicative of underweight, >25 kg m indicating overweight and > 30 kg m-2 obesity. There are, however, some international discrepancies in interpretation. In the US overweight has also been defined as a BMI of >/- 27.8 kg m-2 for men and >/-27.3 kg m-2 for women [ 4]. Despite some cultural variations in interpretation, the BMI provides a useful general health risk predictor. In a study of women aged > 30 years who have never smoked and whose weight has recently been stable, it was found that the relative risk of death from all causes was: 1.0 in those with a BMI of < 19; 1.2 in those with a BMI of 19-24.9, 1.3 for a BMI of 25-26.9, 1.6 for a BMI of 27-28.9, 2.1 in those with a BMI of 29-31.9 and 2.2 when the BMI was > 32 kg m-2 [ 5]. The body weight which has been suggested as optimal with respect to cardiovascular risk is a BMI of 22.6 kg m-2 in men and 21.1 kg m-2 in women [ 16]. BMI is the anthropological measure which shows the highest correlation with systolic blood pressure [ 7].

Another anthropological measure which has been specifically linked to cardiovascular risk is an increased waist:hip ratio. A waist circumference of >/- 94 cm in men and >/- 80 cm in women appears to correlate with a BMI of >/- 25 kg m-2. A waist circumference of >/- 102 cm in men and >/- 88 cm in women correlates with a BMI of at least 30 kg m-2 Using the above measurement criteria, the sensitivity and specificity of waist measurement is 96% and 98% respectively [ 8]. A waist circumference exceeding 94 cm in men and 80 cm in women correctly identified subjects with BMI of >/- 25 kg m-2 and waist:hip ratios >/- 0.95 in men and >/- 80 in women with a sensitivity and specificity of at least: 96% [ 9].

A larger waist circumference reflects intra-abdominal rather than subcutaneous fat [ 10] and, as waist circumference represents metabolically active fat deposits, this measure may be used to identify people at increased cardiovascular risk. An increased waist: hip ratio is associated with an increased risk of non-insulin dependent diabetes and other abnormalities of glucose metabolism [ 11-14]. In a study of over 900 men, waist: stature ratio showed tile highest overall sensitivity and specificity for hypertension, triglycerides and total cholesterol [ 7].

A low fat, high complex carbohydrate diet is becoming increasingly popular as a feasible strategy for long-term weight control. As gram for gram, fat is more than double the energy density of carbohydrate and protein this would seem a rational approach. Furthermore, regression of coronary atherosclerosis has been angiographically demonstrated in persons who, along with lifestyle changes, limited their dietary fat to no more than 10% of total energy and permitted 5 mg/day of cholesterol [ 15]. While such a dietary change has been shown to reduce serum cholesterol to levels at which the mortality associated with ischaemic heart disease is reduced [ 16, 17], it is also the nature of the dietary fat consumed which has implications for cardiovascular health. A diet relatively rich in monounsaturated fat has been shown to promote a healthy lipid profile [118-20]. In contrast to saturated fats which raise total cholesterol, monounsaturated fats have been found to lower total cholesterol. Monounsaturated fatty acids are postulated to lower low-density lipoprotein (LDL) levels [ 21], and raise HDL cholesterol [ 22]. Although polyunsaturated fats do achieve lower total cholesterol levels than monounsaturated fats, this is attributable to polyunsaturated fats lowering HDL as well as LDL. A low HDL has been found to predict coronary artery disease at all levels of cholesterol [ 23]. An additional potential disadvantage of polyunsaturated fatty acids compared to monounsaturated fat is the number of unsaturated bonds. There is a greater propensity for lipid peroxidation in a diet rich in polyunsaturated fatty acid [ 24] and oxidized rather than native LDL is a coronary risk factor.

The beneficial effects of reducing serum cholesterol are age related. A reduction of 0.6 mmol/L-1 of serum cholesterol achieves a 54% decrease of ischaemic heart disease at age 40 years, a 39% decrease at 50 years and 27% decrease at 60 years [ 25]. Acquisition of good dietary habits in earlier rather than later life would seem a reasonable approach. An approved intake is to derive 1: > 1 [ 26]. A previous study has shown that such diets can be formulated [ 27]. Whether such diets are practical for free living individuals has yet to be demonstrated. It was therefore decided to invite a group of healthy young Australian adults to ascertain whether a diet which favoured monounsaturated fats was feasible.

METHOD

Second year students training as registered health professionals were required as part of their coursework to undertake a computer-assisted dietary analysis. All food and drink consumed during the study period was weighed using a digital scale. Data were then analyzed using the Diet/3 nutrient analysis Xyris software. This system is based upon the 1992 NUTTAB database and provides information on the composition of Australian foods. In cases in which food items were not found on the computer database, participants were requested to incorporate any nutritional data provided on packaged food and refer to the latest edition of the Tables of Composition of Australian Foods [ 28]. Participants were cautioned to select days which reflected their usual dietary behaviour and advised to measure their intake on a minimum of two work and one weekend days.

Participants were requested to analyze their usual diet and modify this diet so that their major fat intake was in the form of monounsaturated fatty acids. Once they had formulated a diet conducive to cardiovascular health, participants were requested to implement their proposed diet. Problems with implementing the proposed diet were to be identified and any dietary modifications required to make the diet acceptable were to be documented and computer analyzed.

Throughout the study students were requested to remain cognizant of dietary recommendations promulgated to minimize the risk of cancer and promote cardiovascular and skeletal health. They were also cautioned to scrutinize any vitamin, mineral and fibre repercussions of dietary changes undertaken to optimize fatty acid intake.

RESULTS

Seventy-nine students, 53 females and 26 males, completed the assignment. The average age of female participants was 21.3 years, the mode was 19, the median 20 and the age range 19-30 years. The average age of male participants was 24.2 years, the mode was 21, the median 23 and the age range 19-43 years. Sixteen students, eight of each sex, failed to supply waist measurements and were excluded from further analysis.

Of the remaining 45 females, three were underweight and three were overweight (see Table 1). Five females had an 'at risk' waist measurement. The three females who were overweight and had an 'at risk' waist measurement successfully changed the ratio of their fatty acid intake by reducing their absolute fat intake and the amount of energy derived from fat. The three underweight females also successfully changed their diet to one more conducive to cardiovascular health. Of the two females with an acceptable BMI and an 'at risk' waist measurement, one had a high polyunsaturated fat intake, the other a high saturated fat intake. The subject with a high saturated fat intake was unsuccessful in her attempt to convert to a more 'healthy heart' diet. Thirty-three of the female subjects had diets relatively rich in saturated fat. Fifteen successfully implemented diets with a fat intake conducive to cardiovascular health. The remainder were unsuccessful although six achieved marked dietary improvement. On entering the study, eight females were found to have a diet which favoured monounsaturated fats; three of these consumed > 30% of their energy from fat. Overall 16 females derived > 30% of their energy from fat. All but one of those who successfully increased their relative intake of monounsaturated fatty acids had < 30% of their total energy intake from fat. The one who increased fat as an energy source, from 30% to 31%, reduced her absolute fat intake by 16 g. Of the 18 males who were analyzed, two were overweight and one was obese (see Table 2). The two overweight males also had waist measurements in the increased risk zone. Of these three, only two had a relatively high saturated fat intake and both succeeded in increasing their monounsaturated fat intake. One of the overweight males consumed a diet rich in monounsaturated fats. His absolute daily fat intake was 56 g, 28% of his energy was from fat and his cholesterol intake was 313 mg/day. Three males were found to consume a diet rich in monounsaturated fat, one of these obtained 44% of his total energy from fat. Thirteen males derived the greatest proportion of their fatty acids from saturated fat. Four were unsuccessful in their attempt to implement a diet in which monounsaturated fat was the dominant fat source. One of these did, however, substantially reduce his relative consumption of saturated fat. Of those who did implement a diet in which monounsaturated fat was the major fatty acid, nine simultaneously decreased the amount of energy derived from fat and reduced their absolute intake of fat. One male achieved the desired fatty acid ratio by increasing the energy derived from fat from 23% to 25% and his absolute daily fat consumption from 61 g to 68 g. This male was overweight and had an 'at risk' waist measurement. A total of eight males consumed > 30% of their energy as fat. None of those who modified their relative intake of monounsaturated fat exceeded the 30% recommendation.

Participants who found themselves unable to implement their proposed diet indicated that the major barriers to adherence were cost and inconvenience.

DISCUSSION

The correlation between BMI and waist measurement in this study was less than perfect. This may have been attributable to some intersubject variability in undertaking the measurement. Nonetheless, waist measurement is a better index of blood lipids than BMI [ 7]. Waist measurement reflects changes in intra-abdominal fat due to weight loss and is thought to reflect a genetically determined mechanism underlying body fat distribution. The genetic expression of abdominal fat distribution and atherogenesis is furthermore thought to be enhanced by alcohol and smoking and reduced by exercise. Men with a waist circumference between 94 and 102 cm and women between 80 and 88 cm should be cautioned not to gain weight. Waist measurement can be used to monitor therapy [ 29]. Routine waist measurement may provide a useful personal guideline for self-monitoring cardiovascular risk.

Professional monitoring of cardiovascular risk, while including BMI, places greater emphasis on serum cholesterol and blood pressure measurements. Of all risk factors, it has been estimated that hypercholesterolaemia accounts for 30-40% of all coronary disease, hypertension for 20-25% and smoking for 15% [ 23]. The concentration of monounsaturated fat in the diet has an important impact on serum cholesterol levels ( 18-20). Monounsaturated fat was the major dietary fat in the usual diet of 12 participants. Of these three males and four females also derived < 30% of their energy from fat. Half of the participants were able to improve the fatty acid ratio of their diets and in so doing generally reduced fat as an energy source in their diet. Less successful subjects found that a major incentive to remaining on a diet high in saturated fat was the lower cost and easy access to such foods. A number of participants who were unable to make monounsaturated fat their major fat source did nonetheless modify the nature and the quantity of their dietary fat in a manner consistent with cardiovascular health. Problems with fat intake may, however, persist. A few participants derived extremely little energy from fat. The adequacy of essential fatty acids in a diet which derives < 10% of its energy from fat is questionable, especially in those instances when saturated fats are the major fat source. Cardiovascular disease remains an important cause of death for adults of both sexes. Despite hormonal protection, cardiovascular disease is the second most common cause of death in white females aged 35-39 years and is the leading cause of death in American women > 50 years [ 30-31]. The chronic nature of the disease lends itself to active personal prevention. Individuals need to be empowered to take responsibility for their cardiovascular health. This requires that they gain understanding, make decisions and have personal control in improving their life situation [ 32]. Individuals have a large measure of control over their dietary choices. Selection of a low fat diet rich in monounsaturated fat and self-monitoring of abdominal girth are two measures whereby individuals may be enabled to promote their cardiovascular wellbeing.

CONCLUSIONS

It is possible for free living individuals to derive < 30% of their energy from fat and consume a diet relatively rich in monounsaturated fatty acids. The increased financial cost and relative difficulty in obtaining monounsaturated rich foods may, however, act as a barrier to adhering to such a diet. Nonetheless, self-monitoring of waist measurement and selection of foods low in fat, yet rich in monounsaturated fatty acids, are two practical strategies that individuals can use to manage their cardiovascular health.

TABLE 1. The anthropology and dietary fat consumption of female subjects (n = 45)
Legend for Table:

A - Waist (cm)
B - Cholesterol (%)
C - Fat (%)
D - Fat (g)
E - Cholesterol (mg)
F - Major fatty acid
G - Implemented change[a]

BMI A B C D E

23 70 55 27 45 102
21 72 46 25 60 146
24 81.5 61 19 27.5 69
21 68 54 30 57 85
23.3 89 47 33 93 250
22 68 64 16 33 2657
18 62 44 26 27 144
21 70 52 28 58 160
20 68 38 44 95 272
24 78.5 38 42 100 246
20 67.5 58 25 40.5 88
20 69.5 52 29 38 87
20 69 44 33 50 172
20 58 50 27 42 105
19 63 49 31 55 200
23 75 40 42 100 350
23 72 44 29 58 298
23 72 54 31 47 202
20 66 53 31 54 108
20 64 45 33 60 231
29 85 56 21 34 155
19 68 77 8 12.3 335
21 71 53 29 37 40
23 67.5 38 35 12 280
22 73 48 30 38 142
24 71 42 35 69 216
21 69 50 28 56 133
25 77 46 34 52 177
21 73 53 32 83 170
24 75 53 28 51 128
23 76 44 30 86 400
22 74 59 17 33 145
24 69 49 26 45 192
21 65 52 17 23 153
23 76 46 38 103 215
24 81 48 34 93 205
19 65 59 21 32 51
27 85 49 34 103 260
23 80 52 30 62 108
24 69 57 28 53 65
30 84.5 52 27 49 174
21 73 42 40 100 746
22 67 55 23 37 158
21 80 81 6 9 57
21 80 66 15 24 78

BMI F G

23 Monounsaturated Unnecessary
21 Saturated Unsuccessful
24 Polyunsaturated Improved ratios
21 Saturated Successful ratio change,
fat 27%, 48 g
23.3 Saturated Unsuccessful
22 Saturated Successful ratio change,
fat 12%, 21 g
18 Saturated Successful ratio change,
fat 24%, 30 g
21 Saturated Improved
20 Saturated Successful ratio change,
fat 34%, 79 g
24 Saturated Successful ratio change,
fat 19%, 36 g
20 Monounsaturated Unnecessary
20 Saturated Improved
20 Saturated Improved
20 Monounsaturated Unnecessary
19 Saturated Successful ratio change,
fat 27%, 52 g
23 Saturated Improved
23 Saturated Successful ratio change,
fat 19%, 43 g
23 Saturated Successful ratio change,
fat 26%, 57 g
20 Monounsaturated Unnecessary
20 Saturated Improved
29 Saturated Successful ratio change,
fat 20%, 36 g
19 Polyunsaturated Unsuccessful
21 Polyunsaturated Unsuccessful
23 Monounsaturated Unnecessary
22 Saturated Successful ratio change,
fat 19%, 28 g
24 Monounsaturated Unnecessary
21 Monounsaturated Unnecessary
25 Saturated Improved
21 Saturated Successful ratio change,
fat 19%, 40 g
24 Saturated Successful ratio change,
fat 26%, 52 g
23 Saturated Successful ratio change,
fat 31%, 70 g
22 Saturated Unsuccessful
24 Saturated Unsuccessful
21 Saturated Unsuccessful
23 Monounsaturated Unnecessary
24 Saturated Successful ratio change,
fat 29%, 58 g
19 Saturated Successful ratio change,
fat 18%, 52 g
27 Saturated Successful ratio change,
fat 7%, 14.5 g
23 Saturated Unsuccessful
24 Saturated Unsuccessful
30 Saturated Successful ratio change,
fat 16%, 21 g
21 Saturated Successful ratio change,
fat 29%, 53 g
22 Saturated Unsuccessful
21 Saturated Unsuccessful
21 Saturated Unsuccessful

[a] Implemented change expressed in % of energy
derived from fat and absolute fat retake.
TABLE 2. The anthropology and dietary fat consumption of male subjects (n = 18)
Legend for Table:

A - Waist (cm)
B - Cholesterol (%)
C - Fat (%)
D - Fat (g)
E - Cholesterol *(mg)
F - Major fatty acid
H - Implemented change[a]

BMI A B C D E

23 85 54 27 61 314
20 76 46 35 72 215
28 98 47 28 56 313
25 87 67 12 30 244
24 92 44 27 55 535
27 95 58 23 61 225
24 86 43 38 118 525
21 76 37 39 103 303
32 91 64 14 36 163
25 85 33 36 149 747
23 78 57 21 44 288
25 90 52 32 115 216
21 73 4 38 98 169
20 80 39 44 114 174
22 81 47 36 80 242
22 78.5 74 9 9 79
25 92 48 35 98 106
25 85 54 22 38 216

BMI F G

23 Saturated Successful ratio change, fat 26%, 57 g
20 Saturated Successful ratio change, fat 17%, 35 g
28 Monounsaturated Unnecessary
25 Monounsaturated Unnecessary
24 Saturated Successful ratio change, fat 22%, 49 g
27 Saturated Successful ratio change, fat 25%, 68 g
24 Saturated Successful ratio change, fat 28%, 56 g
21 Saturated Improved
32 Saturated Successful ratio change, fat 7q4, 17 g
25 Saturated Unsuccessful
23 Saturated Successful ratio change, fat 16%, 16 g
25 Saturated Successful ratio change, fat 25%, 67 g
21 Saturated Unsuccessful
20 Monounsaturated Unnecessary
22 Saturated Successful ratio change, fat 24%, 53 g
22 Saturated Unsuccessful
25 Polyunsaturated Unsuccessful
25 Monounsaturated Unnecessary
REFERENCES
[1] Denke MA, Sempos CT, Grundy SM. Excess body weight: an under recognized contributor to high blood cholesterol levels in white American men. Arch Inter Med 1993; 153:1093-1103.

[2] Meisler JG, St Jeor S. Foreward. Am J Clin Nutr 1996; 63:409S-11S.

[3] National Institutes of Health Consensus Development Conference Statement. Health implications of obesity. An Intern Med 1985; 103: 1073-7.

[4] Anon. Leads from the Mortality and Morbidity Weekly Report, CDC. Weight loss regimes among overweight adults--behavioural risk factor surveillance system. 1987. JAMA 1989; 2613: 1163-7.

[5] Mason JE, Willett WC, Stampfer MJ, et al. Body weight and mortality among women. New Eng J Med 1995; 333: 677-85.

[6] Kannel WB, D'Agostino RB, Cobb JL. Effect of weight on cardiovascular disease. Am J Clin Nutr 1996; 63: 419S-22S

[7] Lee JS, Aoki K, Kawakubo K, Gunji A. A study on indices of body fat distribution for screening for obesity. Sangyo Eiseigaku Zasshi 1995; 37: 9-18.

[8] Lean MEJ, Han TS, Morrison CE. Waist circumference as a measure for indicating need for weight management. BMJ 1995; 311: 158-61.

[9] Han TS, van-Leer EM, Seidell JC, Lean ME. Waist circumference action levels in the identification of cardiovascular risk factors: prevalence study in a random sample. BMJ 1995; 311: 1401-5.

[10] Bjorntorp P. Classification of obese patients and complications related to the distribution of surplus fat. Am J Clin Nutr 1987; 45: 1120-5.

[11] Kissebah Alt, Vydelingum N, Muray R, Evans DJ, Hartz AJ, Kalkhof RK, et al. Relation of body fat distribution to metabolic complications of obesity. J Clin Endocrinol Metab 1982; 54: 254-60.

[12] Shumin Z, Folsom AR, Flack JM, Liu K. Body fat distribution before pregnancy and gestational diabetes: findings from coronary artery risk development in young adults (CARDIA) study. BMJ 1995; 311: 1139-40.

[13] Edelson G, Sowers JR. Insulin resistance in hypertension: a focused review. Am J Med Sci 1993; 306: 345-47.

[14] Kohl HW, Gordon NF, Villegas JA, Blair SN. Cardiorespiratory fitness, glycaemic status and mortality risk in men. Diabetes Care 1992; 15: 184-92.

[15] Omish D, Brown SE, Scherwitz LW, et al. Can lifestyle changes reverse coronary disease'? Lancet 1990; 336: 129-33.

[16] Simons L. Lower cholesterol has spectacular benefits. Aust Doctor 18/2/94; 4.

[17] Law MR, Wald NJ, Thompson SG. By how much and how quickly does a reduction in serum cholesterol concentration lower risk of ischaemic heart disease. BMJ 1994; 308: 367-73.

[18] Kushi LH, Lenart EB, Willett WC. Health implications of Mediterranean diets in light of contemporary knowledge. Am J Clin Nutr 1995; 61: 1416S-27S.

[19] Garg A, Bonanome A, Grundy, et al. Comparison of a high carbohydrate diet with a high monounsaturated fat diet in patients with non insulin-dependent diabetes mellitus. New Eng J Med 1988; 319: 829-34.

[20] Garg A, Bantle JP, Henry RR, Coulston AM, Griver KA, Raatz SK, et al. Effects of varying carbohydrate content of diet in patients with non-insulin-dependent diabetes. JAMA 1994; 271: 1421-8.

[21] Grundy SM. Monounsaturated fatty acids, plasma cholesterol, and coronary heart disease. Am J Clin Nutr 1987; 45:1168-75.

[22] Stanton R. Unhealthy confusion over choices of fats. Australian Doctor 27/8/93; 62-3.

[23] Barter PJ. Management of low HDL cholesterol. Aust Fam Phys 1995; 24: 2066-74.

[24] Berry EM, Eisenberg S, Haratz D, Friedlander Y, Norman Y, Kaufman NA, Stein Y. Effects of diets rich in monounsaturated fatty acids on plasma lipoprotiens--the Jerusalem Nutrition Study: high MUFAs vs high PUFAs. Am J Clin Nutr 1991; 53: 899-907.

[25] Law MR, Wald NJ, Thompson SG. By how much and how quickly does a reduction in serum cholesterol concentration lower risk of ischaemic heart disease. Brit Med J 1994; 308: 367--73.

[26] Fifth Report of the National Cholesterol Education Program expert panel on detection, evaluation and treatment of high blood cholesterol in adults. Arch Intern Med 1988; 148: 36-69.

[27] Jamison JR. Dietary fat consumption: a descriptive study of young health aware adults. J Nutr Environ Med 1996; 6:149-60.

[28] Cashel K, English R, Lewis J. Composition of foods: Australia. Nutrition Section Department of Community Services & Health, Canberra: AGPS, 1989.

[29] Van der Kooy K, Leenen R, Seidell JC, Deurenberg P, Hautvast GAJ. Effect of a weight cycle on visceral fat accumulation. Am J Clin Nutr 1993; 58: 853-7.

[30] Wingate S. Women and coronary heart disease. Implications for the critical care setting. Focus Crit Care/1991; 18: 212-20.

[31] Kitler ME. Coronary disease: are there gender differences? Eur Heart J 1994; 15: 409-17.

[32] Israel BA, Checkoway B, Schulz A, Zimmerman M. Health education and community empowerment: conceptualising and measuring perceptions of individual, organisational and community control. Health Edu Q 1994; 21: 149-70.

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By JENNIFER R. JAMISON, MBBCH, PHD, EDD, RMIT University, Bundoora Campus, Plenty Road, Bundoora, Victoria 3083, Australia

Adapted by MBBCH, PHD, EDD

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