Wanda JE Bemelmans

CONTENTS

  1. 1 Introduction
  2. 2 Characteristics of MARGARIN Project
  3. 3 Content of Nutritional Education Program
  4. 4 Results
  5. 5 Discussion: How Do Results Compare to Other Research?
  6. 6 Conclusion References
  7. 1 INTRODUCTION

Traditional risk factors for coronary heart disease (CHD) that can be modified by changing dietary intake include hypercholesterolemia, hypertension, being overweight, and diabetes mellitus. Overall, changing dietary habits toward a more healthy diet will decrease incidence and mortality of CHD.1 Consensus more or less covers the key nutritional messages that effectively prevent CHD. These include limited intake of saturated fat, consumption of many fruits and vegetables, and increased intake of fatty fish.2

During the 1990s, secondary prevention studies showed remarkable reductions in CHD and total mortality in the intervention groups who obtained dietary guidelines comparable with current dietary guidelines.3,4 It should be stressed that the beneficial effect of the dietary therapy was not mediated entirely by effects on established cardiovascular risk factors. For example, in the Lyon Diet Heart Study, serum cholesterol levels dropped by 5% in both intervention and control groups. Hence, it is important to realize that nutritional education can prevent the onset of CHD by mechanistic pathways that are partially independent of effects on traditional CHD risk factors.

Nevertheless, in usual health care, the effects of nutritional health education are evaluated primarily in terms of their effects on total cholesterol level and blood pressure. According to the guidelines for treating hypercholesterolemia and hypertension, the first step should be providing nutritional advice.5,6 Some patients are indicated to receive dietary therapy only because prescribing medication is not considered cost effective. However, numerous barriers exist in providing dietary therapy in the course of usual health care, for example limited nutritional knowledge and time of physicians and insufficient dietary compliance by patients. Furthermore, limited data exist on the most effective way of providing nutritional education as part of usual health care,7

In the northern region of the Netherlands, we executed a primary prevention project focused on coronary heart disease (the MARGARIN project). Patients included had at least three cardiovascular risk factors. The effects of a nutritional education program including group meetings organized by a dietician (intervention group) were compared to the effects of mailed leaflets containing the usual guidelines (control group) during 3 years of follow-up. The latter intervention is comparable to "care as usual." This chapter describes the results on cardiovascular risk factors and dietary intake. The discussion paragraph explains the results in comparison with other research.

5.2 CHARACTERISTICS OF MARGARIN PROJECT

The study design and characteristics of the MARGARIN project, an acronym of Mediterranean Alpha-linolenic enRiched Groningen dietARy INtervention study, have been described in detail elsewhere.8 One of the main research questions was to compare the effects of a nutritional education program (intervention group) to the effects of a printed leaflet sent by regular mail to a control group. This chapter describes the results with respect to total cholesterol level, blood pressure, body mass index (BMI), and dietary intake.

The baseline examinations of the MARGARIN project were performed in November 1997 and follow-up investigations were organized after 16 weeks and 1, 2, and 3 years. During examinations, several cardiovascular risk factors were assessed and dietary intake was measured by self-administered semi-quantitative food frequency questionnaires. Participants were eligible for inclusion if they had elevated serum total cholesterol levels (6.0 to 8.0 mmol/l) and at least two of the following cardiovascular risk factors: high blood pressure or use of antihypertensive medication, BMI > 27 kg/m2, present smoking, and a (family) history of CHD. Exclusion criteria were diabetes mellitus, hypothyroidism, and use of acetylsalicylic acid, anticoagulants, or lipid lowering drugs. At baseline, 266 participants completed the examinations (intervention group n = 103, control group n = 163). During the 3-year study period, 29% of the intervention group and 34% of the control group dropped out for several reasons.

5.3 CONTENT OF NUTRITIONAL EDUCATION PROGRAM

The intervention group was divided into groups of 10 persons, and all subjects were invited to attend three 2-hour meetings organized in March 1998 (the first year of the project). At least two meetings were attended by 68% of men and 78% of women.

Four booklets with core information were distributed and also sent to participants who did not attend the meeting. In the second year of the project, in March 1999, the research dietician organized a 2-hour meeting that focused on reduction of weight. The meeting started with a brief reinforcement of the prior educational messages. In the third year of the project, every participant was invited to a screening for physical fitness. The intervention group was offered a physical training program (2 hours a week). In addition to the educational meetings, the messages were reinforced by written correspondence once a year. The specific dietary guidelines were daily consumption of 5 to 7 slices of bread, 200 to 400 g of vegetables, two pieces of fruit, two to three dairy products, and fish twice a week at dinner.

During the first year, the control group was sent a leaflet containing standard nutritional guidelines via regular mail. In the third year, the control group was invited to a screening test for physical fitness, but was not offered the opportunity to participate in the organized exercise program. The specific dietary guidelines of the control group differed a little from those of the intervention group because the usual Dutch guidelines at that time did not include specific advice on fish consumption. It should be noted, however, that both intervention and control groups of the MAR-GARIN project had free access to a margarine rich in polyunsaturated fatty acids during the first 2 years of the project. This second intervention of this study is described in more detail elsewhere.8

5.4 RESULTS

At baseline, the intervention group (IG) included fewer men (37%) than the control group (CG, 49%) and more users of antihypertensive medication (IG = 57%, CG = 43%; p < 0.05). No significant baseline differences existed in cardiovascular risk factors and dietary intakes between intervention and control groups (Table 5.1).

After 3 years, the BMI increased by 2% in both IG and CG, and systolic blood pressure increased by 1.4 mmHg (1%) in the IG and by 2.9 mmHg (2%) in the CG. Serum total cholesterol levels decreased by 4% in the IG and by 6% in the CG. During the study period, approximately 12% of the IG and 6% of the CG started to use lipid lowering drugs. The use of lipid lowering medication was self-reported and some misclassification may have occurred. When persons with decreases over

1.5 mmol/l are excluded from the analyses (IG n = 2, CG n = 13), the total cholesterol level dropped by 4% in the IG and by 2% in the CG.

No significant differences between IG and CG were observed regarding total cholesterol and BMI during 3 years of intervention (Table 5.2). The intervention group tended to have lower blood pressure after 1 year (mean net difference = -2.6 mmHg; p = 0.14). When the analyses excluded users of antihypertensive drugs at baseline (IG n = 40, CG n = 88), systolic blood pressure decreased by -2.9 mmHg in the IG and increased by +0.8 mmHg in the CG after 1 year of follow-up (p of net difference = 0.10). However, this positive effect did not remain after 2 and 3 years of follow-up (data not shown).

Regarding dietary intake, the IG had consistently lower intakes of total and saturated fat and higher fish intakes during the study period. The initial positive effect of fruit consumption was not statistically significant after 2 and 3 years of follow-up (Table 5.2).

TABLE 5.1

Baseline Characteristics of MARGARIN Population

Intervention Group Control Group

Serum total cholesterol (mmol/l) 6.6 (0.7) 6.9 (0.7) 6.6 (0.7) 6.7 (0.8)

Systolic blood pressure (mmHg) 143 (21) 148 (24) 144 (22) 145 (22)

Body mass index (kg/m2) 29.6 (2.7) 29.9 (4.4) 28.7 (3.4) 30.9 (5.7)

Dietary intake:

Serum total cholesterol (mmol/l) 6.6 (0.7) 6.9 (0.7) 6.6 (0.7) 6.7 (0.8)

Systolic blood pressure (mmHg) 143 (21) 148 (24) 144 (22) 145 (22)

Body mass index (kg/m2) 29.6 (2.7) 29.9 (4.4) 28.7 (3.4) 30.9 (5.7)

Dietary intake:

Total fat (% of energy)

38.0 (6.3)

37.5 (7.2)

39.0 (5.7)

37.4 (7.7)

Saturated fat (% of energy)

14.3 (3.2)

13.8 (2.9)

14.1 (3.1)

14.4 (3.6)

Fruits (g/day)

228 (187)

293 (171)

256 (174)

277 (172)

Median

209

271

271

277

Vegetables (g/day)

140 (60)

139 (53)

155 (86)

134 (51)

Median

136

125

129

125

Fish (g/day)

15 (15)

21 (22)

32 (43)a

17 (20)

Median

9

14

19

10

a Difference with intervention group p < 0.05.

a Difference with intervention group p < 0.05.

5.5 DISCUSSION: HOW DO RESULTS COMPARE TO OTHER RESEARCH?

The MARGARIN study showed that group nutritional education had no additional positive effects on cardiovascular risk factors when compared to distribution of a printed leaflet. Regarding dietary intake, however, the nutritional education program significantly decreased intake of total and saturated fat and increased fish consumption in the intervention group.

The study had three main limitations. First, the subjects of the control group had free access to a margarine rich in polyunsaturated fat during the first 2 years of the project. This type of intervention alone is expected to decrease serum total cholesterol. As a result, it became more difficult for the education program to establish additional positive effects, especially during the first 2 years. Second, randomization to type of education was not performed on an individual basis and some baseline differences existed. For example, the intervention group contained a higher proportion of users of antihypertensive medication. Third, the study population reported sufficient fruit intake at baseline. This may indicate that the subjects were already eating according to guidelines ("ceiling effect") or that fruit consumption was overestimated and thus not validly assessed.

In general, characteristics of nutritional intervention studies that influence the effect on cardiovascular risk factors include (1) the intensiveness of the education, (2) period of follow-up, (3) baseline levels of risk factors and dietary intake, and

TABLE 5.2

Net Differences (95% Confidence Interval) between Intervention and Control Groups in Effects on Cardiovascular Risk Factors and Dietary Intake after 1, 2, and 3 Years of Follow-Upa

1 Year

2 Years

3 Years

Serum total cholesterol (mmol/l) b Systolic blood pressure (mmHg) c Body mass index (kg/m2) Dietary intake

Total fat (% of energy) Saturated fat (% of energy) Fruits (g/day) Vegetables (g/day) Fish (g/day)

CG n = 155 0.1 (-0.1, 0.2) -2.6 (-6.2, 0.9) 0.0 (-0.3, 0.3) IG n = 92;

CG n = 148 -2.4 (-3.6, -1.1)d -1.4 (-1.9, -0.9)d 56 (16, 96)d 3 (-16, 21) 18 (11, 25)d

CG n = 142 0.0 (-0.2, 0.2) 0.2 (-3.6, 3.9) 0.2 (-0.2, 0.6) IG n = 81;

CG n = 130 -2.0 (-3.4, -0.6)d -0.9 (-1.4, -0.3)d 35 (-8, 78) 4 (-10, 19) 15 (8, 22)d

CG n = 108 0.1 (-0.1, 0.4) -2.0 (-7.2, 3.1) 0.1 (-0.4, 0.5) IG n = 67;

CG n = 110 -2.0 (-3.7, -0.2)d -1.2 (-2.0, -0.4)d 6 (-34, 46) 21 (1, 41)d 11 (4, 18)d a Negative numbers indicate larger decreases in the intervention group; all analyses have been adjusted for baseline level and gender. b Users of lipid lowering drugs are excluded.

c Adjusted for baseline level, gender, and use of antihypertensive drugs at baseline. d p < 0.05.

(4) established effects on dietary habits, in particular saturated fat intake. Reviews and meta-analyses of nutritional intervention studies are difficult to interpret because the individual studies have heterogeneous designs. Nevertheless, an indication of the average effects is provided. A review by Yu-Poth et al. concluded that serum total cholesterol can be decreased on average by 10%.9 Ebrahim et al. found an average net difference between intervention and control groups of -0.14 mmol/l for serum total cholesterol and -2.7 mmHg for systolic blood pressure.10 Since Ebrahim et al. included studies with a follow-up for only 26 weeks, it is not surprising that the MARGARIN study results (serum total cholesterol decrease of 4% in IG and no difference in CG; mean net difference in systolic blood pressure of -2.6 mmHg after 1 year) are in line with their conclusion.

In general, nutritional education studies with longer periods of follow-up report disappointing effects on established cardiovascular risk factors. However, high quality research in this field of research is scarce7 and the positive results of individual long-term studies should not be denied. For example, Wing et al. reported a net difference in serum total cholesterol between intervention and control groups of -0.30 mmol/l after 2 years of follow-up. The participants were recruited through a newspaper and may have been highly motivated to change their dietary behaviors.11 A large beneficial effect on serum total cholesterol when motivated persons are included was noted by Baer et al.12 In their nonrandomized study, serum total cholesterol decreased by 12% (-0.72 mmol/l) after 1 year of follow-up. The refusals were included as a control group and group serum total cholesterol did not change at all in the control group. It may be concluded that, depending on study characteristics, some moderate positive effects can be achieved on cardiovascular risk factors after longer periods of follow-up.

The MARGARIN study did not succeed in this respect — partly because of limitations of the study design described above. However, regarding dietary intake, the nutritional education program significantly decreased intake of total and saturated fats and increased fish consumption in the intervention group. These results can be considered important regarding prevention of cardiac events. As cited in the introduction, not all positive effects of changed dietary habits are mediated by effects on established cardiovascular risk factors. For example, increased fish intake can be cardioprotective by preventing cardiac arrhythmias.13 It is noteworthy that we could verify the reported fish intake by changes in the fatty acid composition of the cholesteryl ester (unpublished results). Hence, it can be concluded that group nutrition education actually changed dietary behavior. Eventually, these changes are expected to delay onset of coronary heart disease. However, due to limited power, the MARGARIN study could not examine the effects of the nutritional education program on final cardiac events.

5.6 CONCLUSION

The nutritional education program had no additional positive effects on cardiovascular risk factors as compared to a printed leaflet sent by regular mail. However, long-term beneficial effects were established for intake of fish and saturated fats. These dietary changes may prevent occurrence of coronary heart disease by mechanistic pathways that are partially independent of effects on established cardiovascular risk factors.

REFERENCES

  1. Expert Panel on Population Strategies for Blood Cholesterol Reduction, A statement from the National Cholesterol Education Program, National Heart, Lung, and Blood Institute, National Institutes of Health, Circulation, 83, 2154, 1991.
  2. Kromhout, D., Menotti, A., Kesteloot, H., and Sans, S., Prevention of coronary heart disease and lifestyle: evidence from prospective cross-cultural, cohort, and intervention studies, Circulation, 105, 893, 2002.
  3. de Lorgeril, M., Renaud, S., Mamelle, N., et al., Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease, Lancet, 343, 1454, 1994.
  4. Singh, R.B., Dubnov, G., Niaz, M.A., et al., Effect of an Indo-Mediterranean diet on progression of coronary artery disease in high risk patients (Indo-Mediterranean Diet Heart Study): a randomised single-blind trial, Lancet, 360, 1455, 2002.
  5. Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), Executive summary of the Third Report of the National Cholesterol Education Program (NCEP), JAMA, 285, 2846, 2001.
  6. World Health Organization, 1999 International Society of Hypertension guidelines for the management of hypertension, J. Hypert., 17, 151, 1999.
  7. Thompson, R.L., Summerbell, C.D., Hooper, L., Higgins, J.P.T., Little, P.S., Talbot, D., and Ebrahim, S., Dietary advice given by a dietitian versus other health professional or self-help resources to reduce blood cholesterol, Cochrane Library Issue 3, Update Software, Oxford, 2002.
  8. Bemelmans, W.J.E., Broer, J., Feskens, E.J.M., Smit, A.J., Muskiet, F.A.J., Lefrandt, J.D., Bom, V.J.J., May, J.F., and Meyboom-de Jong, B., Effect of an increased intake of a-linolenic acid and group nutritional education on cardiovascular risk factors: the Mediterranean Alpha-linolenic Enriched Groningen Dietary Intervention (MARGA-RIN) study, Am. J. Clin. Nutr., 75, 221, 2002.
  9. Yu-Poth, S., Zhao, G, Etherton, T., Naglak, M., Jonnalagadda, S., and Kris-Etherton, P.M., Effects of the National Cholesterol Education Program's step I and step II dietary intervention programs on cardiovascular disease risk factors: a meta-analysis, Am. J. Clin. Nutr., 69, 632, 1999.
  10. Ebrahim, S. and Davey-Smith, G., Systematic review of randomised controlled trials of multiple risk factor interventions for preventing coronary heart disease, BMJ, 314, 1666, 1997.
  11. Wing, R.R., Venditti, E., Jakicic, J.M., Polley, B.A., and Lang, W., Lifestyle intervention in overweight individuals with a family history of diabetes, Diabetes Care, 21, 350, 1998.
  12. Baer, J.T., Improved plasma cholesterol levels in men after a nutrition education program at the worksite, J. Am. Diet. Assoc, 93, 658, 1993.
  13. Leaf A., The electrophysiological basis for the antiarrhythmic actions of polyunsat-urated fatty acids, Eur. Heart J, 3 (Suppl. D), D98, 2001.
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