Elsevier

Preventive Medicine

Volume 47, Issue 4, October 2008, Pages 378-383
Preventive Medicine

The impact of a population-based multi-factorial lifestyle intervention on changes in long-term dietary habits: The Inter99 study

https://doi.org/10.1016/j.ypmed.2008.05.013Get rights and content

Abstract

Objective

To evaluate the effectiveness of a population-based multi-factorial lifestyle intervention on long-term changes in dietary habits compared to a non-intervention control group.

Methods

The study was a randomized controlled lifestyle intervention study, Inter99 (1999–2006), Copenhagen, Denmark, using a high-risk strategy. Participants in the intervention group (n = 6 091) had at baseline a medical health-examination and a face-to-face lifestyle counselling. Individuals at high risk of ischemic heart disease were repeatedly offered both individual and group-based counselling. The control group (n = 3 324) was followed by questionnaires. Dietary habits were measured by a validated 48-item food frequency questionnaire and changes were analyzed by multilevel analyses.

Results

At the 5-year follow-up the intervention group compared to the control group had significantly increased their intake of vegetables (men: net-change: 23 g/week; p = 0.04; women: net-change: 27 g/week; p = 0.005) and decreased the intake of highly saturated fats used on bread and for cooking (men: OR = 0.59 (0.41–0.86); women: OR = 0.42 (0.30–0.59)). Significant effects on fruit and fish intake were found at the 3-year follow-up but the effect attenuated at the 5-year follow-up.

Conclusion

A population-based multi-factorial lifestyle intervention promoted significant greater beneficial long-term dietary changes compared to the control group, especially the intake of vegetables and saturated fat was improved.

Introduction

Changing the dietary habits of a population towards a higher intake of vegetable oils, fruits, vegetables and fish and a lower intake of animal fat has a great potential in the prevention of cardiovascular disease (Brunner et al., 2005, Hu and Willett, 2002, Matthiessen et al., 2003, World Health Organisation, 2003).

Changing dietary habits is a very complex behavioural process and the effect of behavioural counselling to promote healthy eating in an unselected adult population has been questioned by systematic reviews during recent years (Ammerman et al., 2002, Ebrahim and Davey, 2000, Ketola et al., 2000). The foundation for evaluating the effect individual dietary counselling as a primary prevention strategy to perform healthier diet in the general population is, however, weak as the vast majority of randomized intervention studies have been small and/or performed only in high-risk individuals, post-randomized to intervention or control group. Brunner et al. concluded in a Cochrane review that dietary advice among healthy adults can bring about modest beneficial dietary changes (Brunner et al., 2005). The mean follow-up period in this review however, was only 9 month and therefore the long-term effect is unknown. The few long-term studies performed in the general population did not include a non-intervention control group (Patterson et al., 2004) or did only include minimal intervention (Wilhelmsen et al., 1986). Thus, the long-term effect of lifestyle counselling interventions to improve dietary habits in a general population is still undetermined.

The aim of this study was to evaluate the effectiveness of a population-based multi-factorial lifestyle intervention on long-term changes in dietary habits compared to a non-intervention control group.

Section snippets

Subjects and methods

The study design is described in detail elsewhere (Jorgensen et al., 2003). In short, Inter99 is a population-based randomized lifestyle intervention study aiming to prevent ischemic heart disease (IHD). The study population comprised all 61,301 individuals aged 30, 35, 40, 45, 50, 55 and 60 years living in the western part of Copenhagen County on 2nd December 1998. An age- and sex-stratified random sample of 11,708 individuals was drawn (intervention group) from the study population by the

Physical examinations and risk assessment

All participants in the intervention group were required to fast from midnight on the day of attendance at the centre and they had a thorough health examination. For each participant the absolute risk of IHD within the next 10 years (the Copenhagen Risk Score) was estimated using the computer program PRECARD® (Thomsen et al., 1997). Individuals were categorized as high-risk individuals if they had either an absolute risk in the upper quintile of the distribution stratified according to sex and

Intervention

Based on the personal risk estimate, each individual had a lifestyle counselling talk focussing on smoking, physical activity, diet and alcohol. The staff (doctors, nurses and dieticians) were all trained in health counselling and the motivational interviewing method (Britt et al., 2004). In addition to the health screening program and the individual counselling, high risk individuals were offered group counselling on diet and physical activity or smoking cessation or reduction, depending on

Behavioural models implemented in the Inter99 intervention

Overall the intervention was based on elements from the Health Belief Model (Janz and Becker, 1984), the Social Cognitive Theory (Bandura, 1986) and the Transtheoretical Model (Prochaska et al., 1997). The implementation of these in the intervention is briefly described in the following.

A central educational tool in the Inter99 was the computerized program PRECARD®, a program based on the Health Belief Model (Janz and Becker, 1984). The participants were given a thorough interpretation of the

Follow-up

All individuals in the intervention group belonging to the high-risk group were re-invited after 1 and 3 years for a health examination, completion of a questionnaire, risk assessment and lifestyle counselling. Individuals who still fulfilled the criteria for being at high-risk were again offered group counselling. Low-risk individuals and participants in the control group were followed by questionnaire. At the 5-year follow-up all baseline participants were invited for health examination and

Outcome measurements

Dietary intake was measured using a self-administered 48-item food frequency questionnaire (FFQ). The FFQ included nine categories of questions: 1: Number of meals per day; 2: Type of bread; 3: Type of spread used on bread; 4: Cheese, meat and fish etc. laid on bread; 5: Hot meals; 6: Type of fat used for cooking; 7: Accompaniments to hot meals; 8: Vegetables; 9: Fruits. Category 2, 3 and 6 consisted of one question about the type typical used. The participants were asked to report the type

Covariates

Education was categorized into four categories of vocational training: 1: None, 2:< 2 years; 3: ≤ 2–4 years, 4:< 4–9years. Employment status was classified as 1: employed; 2: unemployed; marital status as: living with a partner (married/cohabiting (yes/no)) and age as 1:30–35; 2:40–50; 3:55–60 years old. Smoking status was recorded in four categories: never smokers; ex-smokers; occasional smokers; and daily smokers. The reported intake of alcoholic beverages was calculated into units of ethanol

Statistical analysis

At baseline in the control group there was a larger proportion of individuals in the lower and upper age group, which reflects differences in the sampling method (Jorgensen et al., 2003). Therefore descriptive analyses comparing baseline characteristics between groups were made using age-adjusted Cochran–Mantel–Haenszel test and age-adjusted linear regression models for continuous variables. Non-responders were defined as missing information on dietary habits at follow-up, either because the

Results

Characteristics of the participants are shown in Table 1. At baseline employment, perceived risk associated with dietary habits and self-rated health in women and smoking habits and perceived risk associated with dietary habits in men differed between groups. Table 2 shows the crude intake of fats, fish, fruit and vegetables at baseline and follow-up. At baseline no significant differences between the intervention group and the control group were found in dietary intake in men, whereas women in

Discussion

This study demonstrates that a multi-factorial intervention is effective in promoting positive dietary changes in an unselected adult population. The intervention appeared to be especially effective in decreasing the intake of saturated fats and increasing the intake of vegetables.

Some of the important previous large-scale long-term intervention studies are the Oslo Study Diet and Antismoking Trial (Hjermann et al., 1981); the Tromsø study (Knutsen and Knutsen, 1991) and the MRFIT study (Kuller

Acknowledgments

We acknowledge all members of the Inter99 team, the participants and the steering committee of the Inter99 study: Torben Jørgensen, DMSc (PI), Knut Borch-Johnsen, DMSc (Co-PI), Hans Ibsen, DMSc, Troels Thomsen, Ph.D, Charlotta Pisinger, PhD and Charlotte Glümer, PhD.

Funding

The study was initiated and analyzed by the investigators in this project, but was supported economically by: The Danish Medical Research Council, The Danish Centre for Evaluation and Health Technology Assessment, Novo

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