DISCUSSION
Nutrition counseling by an FP based on the Stages-of-Change Model, with referral to a dietician in the action stage, successfully changed dietary behavior after 6 months in patients at elevated risk for cardiovascular disease. This success was accompanied by reductions in body weight. Differences in fat intake were sustained at 12 months, but this was not reflected in lower serum lipid concentrations. Initial reductions in energy intake and anthropometric values did not persist after 1 year. Our findings are in line with other dietary intervention studies in family practice that report improved dietary habits but no significant effect on objective cardiovascular risk factors such as body weight and blood lipids.10,25-27 The uniqueness of our study is that it is the first randomized controlled trial in family practice based on the Stages-of-Change Model in which nutrition counseling is managed by the FP.
The reductions we found in total serum cholesterol concentrations (0.9% in the intervention group and 2.3% in the control group after 12 months) were smaller than the 3%-6% suggested by a systematic review of individualized nutrition counseling in free-living subjects.28 The observed reduction in our study is also less than predicted by the Keys equation.29 We do not have a clear explanation for this. It is possible that patients in the intervention group gave more socially desirable answers to the food frequency questionnaire than patients in the control group, due to the more extensive nutrition guidance in the intervention group.
The dropout rate in our study was low: 91% of the patients completed the trial, a notable strength of the study. This may be due to the fact that the participating patients were recruited and treated by their own FP, and may in part account for the small effect size as we avoided the selective participation of those patients who were most motivated for change. The education level of the study sample was low compared with the Dutch population at similar age,30 and this could also have resulted in smaller differences between intervention and control groups. In addition, it has been found that CHD patients who are obese and do not use lipid lowering drugs are less likely to follow recommended cholesterol-lowering diets.31 However, all of these factors make our study representative of the circumstances FPs can expect when managing nutritional intervention in routine care for patients at elevated risk for cardiovascular disease. Nutritional counseling on the basis of the Transtheoretical Model of stages of change7 is effective in the short term, but it is disappointing to have to conclude that this effect appears to be temporary, with eventual rebound to pre-intervention status. No sustained effects on the target outcomes such as body weight and serum lipids were found, possibly due to the relatively short (1-year) observation period. Improved effectiveness might be achieved with the development of patient protocols and education materials that are better aimed at poorly educated persons, and with more extensive use of modern forms of communications to implement lasting changes.
Conclusions
Nutritional counseling based on stages of change in patients at elevated risk for cardiovascular disease, provided by an FP with referral to a dietician in the action stage, led to reductions in dietary fat intake in the short and long term and to weight loss in the short term. In the absence of long-term effects on serum cholesterol levels, the emphasis remains on treating elevated lipids with drugs. However, research on effective and inexpensive dietary interventions remains important because of promising results for the short term and the important advantages of such intervention. The emphasis for future research should be testing new methods to maintain (dietary) behavioral changes and to investigate differences in susceptibility between individuals with unhealthy lifestyles. The model based on stages of change seems well suited for this sort of intervention, and the experience of this study is that it can easily be incorporated into the routines of family practice at low cost. As such, it is a simple instrument for selecting patients who are willing to change their food habits. Further, we reached a high percentage of poorly educated people, who are particularly vulnerable.32 We recommend examining whether education materials need to be better aimed at people with a low socio-economic status. Long-term nutrition counseling is needed for maintenance and further improvements.
Acknowledgments
This research was supported by the Netherlands Heart Foundation under grant no. 97.106 and by Bayer. We are grateful to the staff of the NMP family practices and their patients, without whom this study would not have been possible. We extend special thanks to the dieticians José Veen and Els Siebelink and to all the research assistants, especially to Marjolein Homs.