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Ammerman A, Pignone M, Fernandez L, et al. Counseling to Promote a Healthy Diet [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2002 Apr. (Systematic Evidence Reviews, No. 18.)

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

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Counseling to Promote a Healthy Diet [Internet].

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4Discussion and Conclusions

To provide information for the US Preventive Services Task Force (USPSTF) so that it can update its previous recommendations concerning counseling to promote a healthy diet, we conducted systematic reviews of 2 main bodies of literature and attempted to answer 7 key questions. The first main area included relationships between dietary behaviors and various health outcomes (the diet-health link) (Key Question No. 1 in Chapter III). The second broad area (the remaining key questions in Chapter III) dealt with various aspects of counseling interventions (chiefly in the primary care setting) intended to promote healthy diets (the counseling-diet link), starting with dietary assessment itself. These topics are briefly discussed in turn below.

Table 13 summarizes our judgments about the size and quality of the entire body of evidence. Harris et al. 221 provide USPSTF definitions for internal validity, external validity, and coherence (consistency) of bodies of evidence.

Table 13. Summary of the size and quality of bodies of evidence on key questions.


Table 13. Summary of the size and quality of bodies of evidence on key questions.

The Link between Dietary Patterns and Health Outcomes

Dietary patterns are important determinants of health status. A wide range of observational studies and selected randomized trials have documented the association between multiple dietary behaviors and various health outcomes. The evidence about some specific dietary relationships remains incomplete. Nonetheless, our review suggests that, in general, a diet high in fruits, vegetables, whole grains, fish, and calcium and low in saturated and trans-unsaturated fats is associated with better general health and lower morbidity.

Dietary Assessment

Dietary assessment is the first step in identifying patients in need of counseling and in guiding the practitioner to offer advice that is directly relevant to the patient's dietary habits and the factors that influence them. Only about 23% to 42% of physicians nationally counsel their patients about diet; 90% of primary care providers spend fewer than 5 minutes on dietary assessment.181,222,223 Although few physicians conduct any sort of dietary assessment, those who do are significantly more likely to counsel a larger proportion of their patients.179,224

Although the independent effect of dietary assessment on health outcomes has not been well studied, such evaluations are the first step in nearly all studies that examine the effect of dietary counseling on behavior or health outcomes. To determine nutritional risk and need for counseling intervention, primary care providers need practical and valid means of assessing dietary intake. 225 Instruments that can be scored simply and that guide providers to offer food-based rather than nutrient-based counseling are particularly useful. We identified more than 15 validated and moderately feasible tools for carrying out dietary assessments in primary care patients and settings. Some are age-specific (infants and toddlers, children, adults, and the elderly), and others are designed for specific ethnic or cultural populations.

Assessment questions that can inform counseling by assessing mediators to dietary change (beliefs, barriers, or readiness to make dietary change) are also useful. However, they are only infrequently included in brief assessments.109,111,112,226


Although primary care providers endorse the importance of dietary counseling as part of their professional role, counseling rates are far from what national guidelines recommend. 172,173 Confidence among providers that they can have a positive impact on patient behavior has never been high, and it may be waning in the face of the growing obesity epidemic in this country.166,170,171,177

Impact of Counseling on Dietary Behaviors

Numerous interventions are available to help patients attempting to change their diets. We identified and reviewed a total of 29 separate studies. Nearly half of these dealt with more than one dietary constituent. In all, 25 of these addressed dietary fat; 11, fruit and vegetable intake; and 7, dietary fiber. Overall, such interventions had a modest effect in changing short-term dietary behavior, but the evidence about long-term change is less clear. Publication bias cannot be ruled out, but our findings and those of other systematic reviews support the conclusion that dietary counseling interventions with a wide range of patients and in a wide variety of settings can have a positive impact on dietary fat intake, on fruit and vegetable consumption, and on dietary fiber. These were reported in a total of 33 articles (12 articles dealt with 2 or 3 dietary constituents).

Among the factors affecting the response to dietary counseling, higher risk status of the patient was associated with somewhat greater changes in diet. High-intensity interventions were more likely to produce large changes than lower-intensity interventions, although many high-intensity interventions still produced only small or medium changes.

As expected, those interventions deemed most externally valid (most easily replicated in a standard primary care setting) achieved smaller effects: low- to medium-intensity interventions conducted by primary care providers in the course of their usual activities had only small effects on dietary behavior. Interventions using outside research clinic interventions were generally more effective than those within a primary care clinic. No studies evaluated outside referral to individual counseling or group sessions independent of a research clinic. Computer or mailed interventions have promising effects, especially on consumption of fruits and vegetables. Studies using more counseling elements generally seen as proven to be effective had a greater impact in terms of dietary changes than those using fewer elements.

Only very limited data are available regarding the cost-effectiveness of different dietary intervention approaches. One study suggested that referral to a dietitian with brief physician reinforcement was more cost effective than referral alone. 200 Adverse effects other than costs associated with dietary assessment and /or counseling interventions appear to be limited.

Few dietary counseling interventions designed to reach primary care patients reported including a significant number of the behavior change strategies that we identified from the health behavior literature. This may be related in part to the inability of researchers fully to describe their intervention approach because of journal page limitations or other considerations. Interventions reporting the use of more components were more likely to produce large changes than those using fewer components.

Research Needs

Several areas of controversy remain in defining the relationship between diet and health outcomes. In areas such as cancer risk, further research would help resolve the discrepancies between case-control and cohort studies. More research is also needed to determine better the optimal amount and type of dietary fats that should be included in healthy diets.

Efficient but dietary assessment tools, particularly for children, should be developed and validated. Research is also needed to clarify and evaluate the linkages among dietary screening, additional focused dietary assessment, and assessment-based counseling. Particularly important will be comparisons between these approaches and individual or population-level general dietary advice.

More in-depth examination of the effectiveness of specific components and intensities of dietary counseling is warranted. More theory-based studies will contribute to better understanding of immediate and long-term outcomes of dietary counseling. The lack of studies evaluating physician referral to health professionals outside their clinic setting for either one-on-one or group counseling is striking. Studies of dietary interventions delivered by special research clinics are common, but they are not representative of the resources commonly available to primary care providers. Cost-effectiveness studies comparing different intervention strategies relevant to primary care are lacking, but they will be particularly important in evaluating technology-based intervention strategies. Finally, as we move toward more environmental and policy-level interventions to support individual-level change, investigations should be carried out to evaluate the potential role and impact of the primary care provider in either stimulating or reinforcing these interventions.

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