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IJE Advance Access originally published online on September 12, 2005
International Journal of Epidemiology 2006 35(2):409-415; doi:10.1093/ije/dyi170
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Published by Oxford University Press on behalf of the International Epidemiological Association © The Author 2005; all rights reserved.

Nutrition

Randomized controlled trial: effect of nutritional counselling in general practice

Carlotta Sacerdote1, Laura Fiorini1, Rosalba Rosato1, Michela Audenino2, Mario Valpreda2 and Paolo Vineis3,4,*

1 CPO-Piemonte, Torino, Italy
2 Health Regional Administration of Piedmont, Torino, Italy
3 Imperial College, London, UK
4 University of Torino, Italy

* Corresponding author. Department of Epidemiology and Public Health, Imperial College of Science, Technology and Medicine, Norfolk Place, W2 1PG London, UK. E-mail: p.vineis{at}imperial.ac.uk


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Declaration of Interest
 References
 
Objectives To investigate the effectiveness of a non-structured 15-min educational intervention by general practitioners (GPs) on modifications of daily diet among healthy adults.

Design Two arms randomized trial lasting 12 months.

Setting Italian general practitioner wards.

Subjects A total of 3186 men and women aged 18–65 years recruited in the medical ward by their GPs.

Interventions An educational intervention and a brochure on the basics of a healthy diet based on the Italian Guidelines for a Correct Nutrition, 1998. The main study goal was to attain an intake of fruits and vegetables >5 servings per day. Follow-up visit every 6 months.

Main outcome measures Weight, blood pressure, and a 40-items Food Frequency Questionnaire.

Results The intervention group showed a slightly reduced net intake of meat and a slightly increased net intake of fruits and vegetables, fish products, and olive oil. Body mass index (BMI) changed only in the treatment arm [–0.41 95% confidence interval (95% CI) –0.11 to –0.53]. The net change at 1 year in the intervention arm was +1.31 (CI 0.90–4.39) for fruits and vegetables, and –0.22 (–0.11 to –0.69) for meat (portions per week). We also computed a ‘healthy diet score’ reflecting compliance with recommended dietary habits. In the intervention group, the mean score at recruitment was significantly lower than the mean score at the end of follow-up (Crude score change = 0.29; CI 0.19–0.48). No differences were observed in the control group (Crude score change = –0.04; CI –0.22–0.02). The difference in score from baseline to the final visit, comparing the intervention vs the control group, was statistically significant (P < 0.001) (MANOVA adjusted by sex, BMI, education, and time).

Conclusions A brief educational intervention by GPs can induce multiple diet changes that may lower BMI and potentially reduce chronic disease risk in generally healthy adults.

Keywords Randomized controlled trial, general practice, nutrition, health promotion

Accepted 26 July 2005


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Declaration of Interest
 References
 
Dietary changes are believed to contribute to better health, but the evidence is still uncertain, particularly for the role of red meat, fish, and other constituents of the diet.1–8 Consumption of fruits and vegetables, in particular, is thought to protect our body against epithelial cancer and cardiovascular diseases.1,2

In spite of such evidence only 38% of the Italian population eat at least 5 portions of fruits or vegetables a day.3 Nutrition guidance by family doctors can be an important source of preventive information for the population. In fact most patients cite their physicians as credible sources of nutrition suggestions.4

Systematic reviews suggest that some kinds of dietary intervention can be effective in reaching the expected goals, usually losing weight, reducing blood pressure, or modifying the balance between different dietary components.5,6 In particular, goal-setting seems to be a promising technique.7 Such reviews tend to suggest that dieticians can be better than nurses or doctors in achieving the expected goals.8 However, studies on general practitioners (GPs) are not many, and the involvement of GPs in dietary prevention deserves to be studied more thoroughly.5,7,8 In one study conducted in a general practice environment, a 6-month, randomized, controlled trial of a brief negotiation method was undertook to encourage an increase in consumption of fruits and vegetables to at least five daily portions. The authors obtained statistically significant differences between arms for a number of outcomes (antioxidants in plasma, blood pressure, and portions of fruits and vegetables). However, the intervention was administered by nurses, not by doctors.9

The present study was designed to test the hypothesis that an educational intervention carried out by GPs could be successful in improving nutritional habits and reducing risk factors such as overweight and high pressure.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 Declaration of Interest
 References
 
We conform to the CONSORT guidelines in the description of our study (http://www.consort-statement.org).

Participants
All patients aged 18–65 years attending the wards of 33 selected GPs (in the cities of Torino and Asti, Italy) were eligible if they were not obese [body mass index, (BMI) < 30] or affected by chronic or severe diseases.

In Italy, primary care physicians offer the first level assistance to the population (excluding emergencies). All Italian citizens have free access to primary care physician wards that are part of the National Health System. The role of primary care physicians in Italy is to make periodic check up visits, to assist patients for minor and chronic diseases, to address patients to specialists, and also to offer primary and secondary prevention interventions. GPs were selected through their professional organizations as those most motivated in the trial. Each GP participated in a 4-day course on nutrition carried out by clinical nutritionists. Only patients who visited their GP for reasons unrelated to gastrointestinal problems, and without dietary restrictions, were enrolled. There is no evidence that the prevalence of symptoms that could lead to changes in diet differed between the two arms.

Interventions
All patients had their weight and blood pressure measured by the GP and were given appointments to return to the ward twice in one year. At each of the three visits the GP collected a 40-items food frequency questionnairse (FFQ), a brief lifestyle questionnaire, and the anthropometric measures from both groups. The FFQ investigated the weekly consumption of main food groups: fruiting vegetables; tomatoes; leafy vegetables; root vegetables; mixed salad and mixed vegetables; soups; cabbages; legumes; potatoes; citrus fruits; other fruits; milk yogurt; cheeses (including fresh cheeses); pasta, bread, flour, flakes, and other grains; rice; beef, veal, and pork; rabbit and chicken/turkey; offals; fish, crustaceans, and molluscs; egg; olive oil; vegetable oils (no olive); butter; margarines; other animal fat; sugar, honey, jam, chocolate, cakes, and biscuits; carbonated/soft/isotonic drinks; wine; beer and cider; liqueurs; and snacks. The food consumption was assessed in units of self-reported standard servings (e.g. a cup, half plate, and a spoon). This questionnaire was a simplified version of the EPIC questionnaire, which was validated in our context within a pilot study.10 The average servings of endpoint food items have been estimated in our population by the EPIC 24 h recall questionnaire (fruits and vegetables = 148 g, fish = 150 g, and red meat = 162 g). Blood pressure was measured according to the WHO guidelines.

At the first visit to the intervention group the GP administered a 15-min personalized nutritional intervention, based on a brochure about diet and health that summarized the Italian Guidelines for a Correct Nutrition 199811 and on a short explanation by the GP. The intervention was focused on the importance of higher consumption of fruits, vegetables, fish, and olive oil and lower consumption of red meat, snacks, and sweets, and was modulated on the basis of sex- and age-specific energy consumption and on unbalanced nutritional habits of each subject. The control group received ‘sham’ intervention, i.e. a simpler and non-personalized conversation without the use of a brochure. This guaranteed at least partial blindness. In the follow-up visits no other message was administered to either group. A dietician checked all questionnaires for completeness, internal coherence, and plausibility.

Specific objectives and outcomes
The main goals of the study were to attain in the intervention group consumption of >5 servings a day of fruits and vegetables, of >1 serving a week of fish, of <3 servings a week of red meat, of olive oil in place of other fats, and to attain a BMI between 19 and 25 (normal weight) and a normal blood pressure (SBP ≤ 140 mmHg and DBP ≤ 90 mmHg) (Figure 1).


Figure 1
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  		Figure 1 Study endpoints

 
Sample size
We have computed the sample size required to obtain a statistically significant difference between the two arms for the main study objective, an intake of fruits and vegetables >5 servings per day in the intervention group and an intake of 2.8 servings per day in the control group (current average number of servings of fruits and vegetables for the Italian population12). With {alpha} = 0.05 and ß = 0.8 (two side-test) we required ≥1200 subjects per arm.

Randomization
A progressive number was assigned to each eligible patient who attended the selected wards during 6 months. Randomization was performed by the Project Manager, who randomly selected the patients from each ward and assigned the subjects to two groups. Random numbers were generated by using the computer. The sequence was concealed until interventions were assigned. The selected patients were invited to participate in the study and to sign a consent form. Both participants and all the personnel were blind as to the group assignment, except for the GP, who was expected to release the intervention.

Statistical methods
Data analyses were performed using the SAS package for Personal Computer (SAS Inc. V 8.2, Cary, NC). We have shown analyses for patients attending both FU visits.

We created a ‘healthy diet score’, based on fruits and vegetables, fish, red meat, and olive oil intake, to assess the diets of all participants. The score is justified by the need of having an overall indicator of efficacy of the intervention, thus reducing multiple comparisons. However, we also show data for individual dietary items. For fruits and vegetables, for which there is strong evidence of protection from higher intake, we assigned a weight of 2 if a participant consumed >5 servings a day, a score of 1 for 5 servings a day, and a score of -1 for lower intakes. We used the same method to weigh the consumption of fish (weights 1 to –1) and olive oil (weights 1 to –1). For the consumption of red meat we assigned a weight of 0 if a participant consumed more than 3 servings a week and a score of 1 if (s)he followed the Italian nutritional recommendations (<3 servings a week). The total score ranges from –3 (low quality diet) to 5 (high quality diet).

We used a multivariate analysis of variance (MANOVA) to evaluate changes in the outcome variables from baseline to 1 year of follow-up, according to intervention. The differences were adjusted by sex, BMI, and education.

We calculated the probability of achieving normal weight and normal blood pressure, and of complying with the recommended dietary endpoints, by using logistic regression models. Odds ratios (ORs) and 95% confidence intervals (CIs) are adjusted by sex, BMI, and education.

All performed analyses are intention-to-treat. We assumed that those individuals who failed to attend their final visit did not change their diets from the baseline, and these values were therefore imputed.

Ethical approval
All participants signed an informed consent form. The trial was approved by the ethical committee of the Department of Biomedical Sciences and Human Oncology, University of Torino, and was monitored by the Association of General Practitioners of the Province of Torino.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Declaration of Interest
 References
 
Participant flow and baseline data
A total of 3186 participants were enrolled in the study (Figure 2). Baseline characteristics were similar in the randomized groups (Table 1). Six months after randomization, 99% of participants attended the second visit, while 93% attended all three visits. We have not shown the 6-month data below because they are almost identical to the 1-year data. Patients lost at follow-up were more frequently males, well-educated, and were younger than patients who attended all visits. These differences indeed were not statistically significant. No differences were found in BMI, blood pressure, and food consumption at baseline.


Figure 2
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  		Figure 2 Study enrolment flow chart

 

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  		Table 1 Frequency or mean values (SD) of main variables at baseline and at 1 year of follow-up

 
Outcomes and estimation
Statistically significant differences in weight and diet between the randomized groups were obtained at the end of follow-up. Table 2 shows crude changes and their 95% CIs for intervention outcomes: weight loss occurred only in the treatment group and the improvement in diet (as defined above) occurred in both groups, but changes were more evident in the intervention group. Blood pressure did not differ between the two groups and did not change with time.


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  		Table 2 Crude changes in outcome variables between baseline and 1 year of follow-up

 
Table 3 shows the effects of intervention on the outcome variables, adjusted by sex, BMI education, and time, according to MANOVA. Intervention alone is statistically significant for BMI and consumption of fish only. The effect of time, i.e. changes in both arms in the course of the follow-up, adjusted for intervention and other covariates is not statistically significant.


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  		Table 3 MANOVA considering the effects of intervention and of time, respectively, on changes in outcome variables between baseline and 1 year of follow-up

 
Table 4 shows the numbers of participants who reached the expected goals at the end of follow-up and the corresponding ORs and CIs. The BMI at 1 year of follow-up, compared with the baseline, was decreased by 1.3 and 0.1%, in intervention and control groups, respectively. Overweight participants in the intervention arm had an OR of 1.36 (CI 0.98–1.93) for achieving normal weight at 1 year. Participants in the intervention group with incorrect diet at baseline had increased and significant ORs for reaching appropriate consumptions of fish (OR = 1.84; CI 1.50–2.26), red meat (OR = 1.19; CI 1.01–1.59), and olive oil (OR = 2.51; CI 1.92–3.39). Estimates are adjusted also by BMI to isolate the potential effect on dietary habits alone (not confounded by changes of BMI).


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  		Table 4 Numbers, percent, OR, and 95% CI referring to achievement of the expected goal at 1 year of follow-up (normal weight, normal blood pressure, consumption of >5 servings a day of fruits and vegetables, consumption of >1 serving a week of fish, consumption of <3 servings a week of red meat, and consumption of olive oil in place of other fats)

 
We found statistically significant differences in the ‘healthy diet score’ between the randomized groups at the end of follow-up. In the intervention group, the mean score at recruitment was lower than the mean score at the end of follow-up (crude score change = 0.29; CI 0.19–0.48). No differences were observed in the control group (crude score change = –0.04; CI –0.22–0.02). The difference in score from baseline to the final visit in the intervention versus the control group was statistically significant (P < 0.001) (MANOVA adjusted by sex, BMI, education, and time).

No adverse events have been identified.


   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Declaration of Interest
 References
 
Interpretation
It is believed that primary prevention would greatly benefit from randomized controlled intervention studies.13 Observational studies are frequently affected by bias, particularly deriving from selective participation and low compliance of the recruitees, and by confounding. On the other hand, preventive trials are not easy to conduct, and their results may not be generalizable. Our trial was a pragmatic test of what can be realistically achieved in GP wards to improve dietary habits of healthy subjects. We have found that it is possible to improve dietary habits of people attending GP wards, not only in terms of food items that are eaten but also considering a harder endpoint such as BMI. In fact a brief 15-min intervention resulted in more people attaining a normal BMI at 1 year and eating a ‘healthy diet’. However, it should be noticed that the goal achieved in the intervention group (22 servings/week of fruits and vegetables) was still very far from the recommended intake.

Other large studies have recently demonstrated effectiveness in achieving relevant health goals through health education. The DASH (Dietary Approaches to Stop Hypertension)14 and the DASH-sodium trial15 showed that short-term dietary changes can be achieved and can decrease blood pressure, a goal that we did not attain. The Lyon Diet Heart Study tested whether a Mediterranean-type diet, compared with a prudent Western-type diet, could reduce the recurrence of myocardial infarction. In this study the patients assigned to the experimental group were asked to comply with a diet very similar to the dietary advice received from our intervention group (high consumption of fruits and vegetables, fish, and olive oil, and low consumption of red meat). The study showed that after four years from the randomization most experimental patients were still closely following the recommended diet.16 The DART (Diet and Reinfarction Trial) trial showed an important reduction in 2 year mortality in patients advised to eat fatty fish, but the expected results were not achieved in patients advised to modify fat intake and cereal fibre intake.17,18

The DART study, in contrast with the Lyon study, found that the compliance with recommended dietary habits was poor. We found good compliance with the recommended diet in our population, also after 1 year of follow-up. The DART study recruited only men from a Nordic European country, who may not have ready access to fruits, vegetables, and olive oil, and are not acquainted with their use in regular diet. The Lyon trial and ours recruited both men and women (the latter being usually more open to change) from Mediterranean countries where fruits, vegetables, and olive oil are typical foods from traditional diets. Our study, in contrast with those above, examined an educational intervention performed by GPs, who are cited by most patients as a credible source of health suggestions. We think that this approach could be one of the reasons of the good compliance with the proposed diet.

One additional previous study had characteristics similar to ours, being a randomized controlled trial of a brief negotiation method undertook to encourage an increase in consumption of fruits and vegetables in a general practice environment. The intervention was administered by nurses, not by doctors, and compliance was good. The authors obtained statistically significant differences between arms for several important outcomes (antioxidants in plasma, blood pressure, and portions of fruits and vegetables).15

Generalizability
The strengths of our study are: (i) the large number of subjects, (ii) the high degree of compliance, (iii) the setting of clear and realistic a priori objectives, and (iv) the effectiveness for one of the hard outcome variables (BMI). This study has also some limitations: (i) the short duration of follow-up (we plan longer-term follow-up), (ii) incomplete blindness of participants, and (iii) the use of a self-administered questionnaire. Complete blindness would have been impossible to achieve, and we tried to assure at least partial blindness with a sham intervention in the control group. However, the results show consistent changes (e.g. substitution of red meat with fish) rather than single-item changes that could indicate biased reporting. In addition, a dietician checked all questionnaires for completeness, internal coherence, and plausibility. Also, BMI changes were correlated with dietary changes at the individual level. The reasons why the trial was not successful in achieving the goal of a blood pressure reduction are unclear: they can include short duration of both intervention and follow-up, or poor compliance of physicians with guidelines for pressure measurement, entailing random misclassification (however, there was no evidence of digit preference).

Some degree of ‘cointervention’ (particularly the influence of the media and possibly of the sham intervention) may have occurred since the control group also showed similar but smaller changes.

Overall evidence
Dietary counselling by the GP may be an easy way to improve dietary habits in the general population. As the present study shows, encouraging short-term changes in lifestyle can be achieved, although a longer follow-up is needed to demonstrate long-term effects.


KEY MESSAGES

  • Improvement of diet is a public health priority in many countries, but few studies of the effects of nutritional counselling in general practice have been reported. We tested, using a large randomized controlled trial, the hypothesis that an educational intervention conducted by GPs would improve eating habits and reduce cardiovascular risk factors.
  • A 15-min personalized nutritional intervention, together with a brochure, given by a GP was compared with a ‘sham’ intervention of non-personalized short conversation only.
  • At 1 year, both trial arms showed reductions in meat intake and increases in fruit and vegetable intake, fish, and olive oil, but the changes were greater in the intervention than in the sham arm with strong evidence against the null hypothesis. There was no strong evidence of changes in blood pressure in either arm, but there was evidence of a reduction in body mass intake in the intervention arm.
  • A brief educational intervention by GPs can induce multiple diet changes that may lower body mass intake and potentially reduce chronic disease risk in healthy adults.

 


   Declaration of Interest
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Declaration of Interest
References
 
The authors have declared no conflict of interest.


   Acknowledgments
 
The authors thank all the GPs who have participated in the study. This study has been made possible by a grant of the Piedmont Regional Administration (Health Department) to PV.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Declaration of Interest
 References
 
1 Vainio H, Bianchini F. IARC Handbooks on Cancer Prevention: Fruit and Vegetables. Lyon: IARC Press 2003.

2 Kris-Etherton PM, Hecker KD, Bonanome A et al. Bioactive compounds in foods: their role in the prevention of cardiovascular disease and cancer. Am J Med 2002;113(suppl. 9B):71S–88S.

3 Istituto Nazionale di Statistica. I consumi delle Famiglie in Italia—Anno 2001. Istituto Nazionale di Statistica, 2002.

4 Hunt JR, Kristal AR, White E, Lynch JC, Fries E. Physician recommendation for dietary change: the prevalence and impact in a population-based sample. Am J Public Health 1995;85:722–26.[Abstract/Free Full Text]

5 Hooper L, Bartlett C, Davey SG, Ebrahim S. Advice to reduce dietary salt for prevention of cardiovascular disease. Cochrane Database Syst Rev 2004;1:CD003656.

6 Thompson RL, Summerbell CD, Hooper L, Higgins JP, Little PS, Talbot D, Ebrahim S. Dietary advice given by a dietitian versus other health professional or self-help resources to reduce blood cholesterol. Cochrane Database Syst Rev 2003;3:CD001366.

7 Shilts MK, Horowitz M, Townsend MS. Goal setting as a strategy for dietary and physical activity behavior change: a review of the literature. Am J Health Promot 2004;19:81–93.[ISI][Medline]

8 Thompson RL, Summerbell CD, Hooper L et al. Relative efficacy of differential methods of dietary advice: a systematic review. Am J Clin Nutr 2003;77(suppl. 4):1052S–1057S.[Abstract/Free Full Text]

12 John JH, Ziebland S, Yudkin P, Roe LS, Neil HA, Oxford Fruit and Vegetable Study Group. Effects of fruit and vegetable consumption on plasma antioxidant concentrations and blood pressure: a randomised controlled trial. Lancet 2002;359:1969–74.[CrossRef][ISI][Medline]

13 Kroke A, Klipstein-Grobusch K, Voss S et al. Validation of a self-administered food-frequency questionnaire administered in the European Prospective Investigation into Cancer and Nutrition (EPIC) Study: comparison of energy, protein, and macronutrient intakes estimated with the doubly labeled water, urinary nitrogen, and repeated 24-h dietary recall methods. Am J Clin Nutr 1999;70:439–47.[Abstract/Free Full Text]

9 Società Italiana di nutrizione umana. Livelli di assunzione giornalieri raccomandati di energia e nutrienti per la popolazione italiana (Italian Guidelines for a correct nutrition). Available at: http://www.sinu.it/larn.asp

10 Turrini A, Saba A, Perrone D, Cialfa E. Food consumption patterns in Italy: the INN-CA study 1994-1996. Eur J Clin Nutr 2001;55:571–88.[CrossRef][ISI][Medline]

11 Flay BR. Efficacy and effectiveness trials (and other phases of research) in the development of health promotion programs. Prev Med 1986; 15:451–74.[CrossRef][ISI][Medline]

14 Kolasa KM. Dietary Approaches to Stop Hypertension (DASH) in clinical practice: a primary care experience. Clin Cardiol 1999; 22(suppl. 7):III16–22.[Medline]

15 Vollmer WM, Sacks FM, Ard J et al. Effects of diet and sodium intake on blood pressure: subgroup analysis of the DASH-sodium trial. Ann Intern Med 2001;135:1019–28.[Abstract/Free Full Text]

16 De Lorgeril M, Salen P, Martin JL, Monjaud I, Dalaye J, Mamelle N. Mediterranean diet, traditional risk factors and the rate of cardiovascular complications after myocardial infarction: final report of the Lyon Diet Heart Study. Circulation 1999;99:779–85.[Abstract/Free Full Text]

17 Burr ML, Fehily AM, Gilbert JF et al. Effects of changes in fat, fish and fiber intakes on death and myocardial reinfarction: diet and reinfarction trial (DART). Lancet 1989;2:757–61.[ISI][Medline]

18 Ness Ar, Ashfield-Watt PAL, Whiting JM, Smith GD, Hunghes J, Burr ML. The long-term effect of dietary advice on the diet of men with angina: the diet and angina randomised trial. J Hum Nutr Dietet 2004;17:117–19.[CrossRef][ISI][Medline]


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