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US Preventive Services Task Force. Guide to Clinical Preventive Services: Periodic Updates [Internet]. 3rd edition. Rockville (MD): Agency for Healthcare Research and Quality (US); 2002-.

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

Cover of Guide to Clinical Preventive Services

Guide to Clinical Preventive Services: Periodic Updates [Internet]. 3rd edition.

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Scientific Evidence

Epidemiology and Clinical Consequences

Consuming a healthy diet is associated with lower risks for chronic disease morbidity and mortality. Four of the 10 leading causes of death—coronary heart disease, some types of cancer, stroke, and type 2 diabetes—are associated with unhealthy diets.2 The relationships between dietary patterns and health outcomes have been examined in a wide range of observational studies and randomized trials with patients at risk for diet‐related chronic disease. The majority of studies show that people consuming diets that are low in fat, saturated fat, trans‐fatty acids, and cholesterol and high in fruits, vegetables, and whole grain products containing fiber have lower rates of morbidity and mortality from coronary heart disease, and possibly several forms of cancer. In addition, one needs to balance calories with physical activity to maintain a healthy weight. The Dietary Guidelines for Americans18 recommend 3 to 5 daily servings of vegetables and vegetable juices, 2 to 4 daily servings of fruits and fruit juices, and 6 to 11 daily servings of grain products, depending on caloric needs. In addition, they recommend a diet that contains less than 10 percent of calories from saturated fat, no more than 30 percent of calories from total fat, and limited consumption of trans‐fatty acids.

Despite well‐established benefits of consuming a healthy diet, more than 80 percent of Americans of all ages eat fewer than the recommended number of daily servings of fruit, vegetables, and grain products and more than the recommended proportions of daily calories from saturated fat and total fat.19 In 1994‐96, 28 percent of people aged 2 years and older consumed at least two daily servings of fruit, 49 percent consumed at least three daily servings of vegetables, 51 percent consumed at least six daily servings of grain products, 36 percent consumed less than 10 percent of daily calories from saturated fat, and 33 percent consumed 30 percent or less of daily calories from total fat.19

Dietary counseling practices of primary care clinicians indicate limited attention to diet modification. In a 1999‐2000 survey of U.S. adults, 33 percent of respondents reported past year physician advice to eat more fruits and vegetables, and 29 percent reported similar advice to reduce dietary fat.20 In another recent survey, 25 percent of adult patients from four community based group family medicine clinics indicated that their physicians had advised them to limit or reduce the amount of fat in their diets.21

Effectiveness of Dietary Counseling

The ideal evidence to support behavioral dietary counseling would link counseling directly to improved health outcomes in randomized controlled clinical trials. In the absence of such evidence, the clinical logic behind counseling is based on a chain of critical assumptions13:

  • The clinician must be able to assess whether a patient is consuming a healthy diet.
  • Critical components of counseling must be routinely replicable.
  • Counseling must lead to sustained improvements in diet.
  • The health benefits of these changes in diet must be established and known to exceed the potential harms of intervention.

A review conducted for the USPSTF identified 21 fair‐to‐good quality randomized controlled clinical trials of dietary counseling among patients without existing diet‐related chronic disease (e.g., coronary heart disease or cancer). Trials had to include followup of at least 3 months after intervention for at least 50 percent of the enrolled subjects and include measures of dietary intake. Studies that assessed only physiologic measures (e.g., lipid levels, weight, or body mass index [BMI]) were not included. Additional details of the inclusion and exclusion criteria, and methods for assessing quality of studies, are described elsewhere.2,22

Most of these trials focused exclusively on dietary counseling, though some targeted diet as part of a broader risk factor modification program that also addressed smoking and sedentary lifestyle.2326 Most studies targeted reductions in total fat or saturated fat intake (n=17).911,1517,2335 Ten studies targeted increased fruit and vegetable intake10,11,14,23,2729,3 4,36,37 and 7 targeted increased intake of fiber and whole grains.9,15,24,28,29,34,38 Most studies (n=11) focused on a single nutrient, although 10 focused on changes in 2 or more nutrients.911,15,23,24,2729,34

Studies were classified by intensity of the interventions evaluated, based on the number and length of counseling sessions, the magnitude and intensity of educational materials provided, and the use of supplemental interventions such as support group sessions or cooking classes. Low‐intensity interventions involved one contact lasting less than 30 minutes. High‐intensity interventions involved more than six contacts lasting more than 30 minutes. Medium‐intensity interventions fell between low‐ and high‐intensity.

Effects of counseling were classified as "large," "medium," or "small" for each component of diet measured.2 With reference to these specific, defined categories, the USPSTF concluded that large effects sustained over time were likely to produce important health benefits (reductions in morbidity and mortality).3943 Given the large attributable risk associated with these dietary components, it is possible that medium or even small changes in diet would yield important health benefits across a large population. However, to date, there is little direct evidence about the effect of small and medium dietary changes on the future risk for coronary heart disease, making it difficult to determine with certainty whether such changes will translate into changes in the incidence of chronic disease. Better data about these linkages are needed.

Assessing Dietary Behaviors in Primary Care Patients

A number of brief, validated dietary assessment instruments can identify dietary counseling needs, guide intervention, and monitor change among adult patients in primary care and other clinical settings. Most of these instruments can be self‐administered, are easily scored, have fewer than 40 items, and take 10 minutes or less to administer. However, these instruments are susceptible to bias (i.e., patients report healthier diets than they actually consume); some studies indicate that under‐reporting of caloric intake is common, especially among obese patients.12 When used to evaluate counseling efficacy, efforts to verify self‐reported information are recommended.912,15,26,44 For children aged 9 years and older, food frequency questionnaires administered directly to children can provide a reasonably accurate picture of usual dietary patterns, with correlations with criterion measures ranging from 0.46 to 0.79.8 No brief valid dietary screening instruments were identified for children below the age of 9 years. The optimal interval for screening adults or children is not known.

Effectiveness of Routine Counseling in Primary Care

The USPSTF found nine fair‐to‐good quality randomized controlled trials of behavioral dietary counseling in unselected populations in primary care settings. The majority of these interventions focused on change in more than one nutrient (i.e., fat/saturated fat, fruit/vegetables, and/or fiber).9,11,15,2729,34 Most of these trials combined basic nutrition education with behaviorally‐oriented counseling to help patients acquire the skills, motivation, or support needed to alter their daily eating patterns and food selection and preparation practices. Duration of interventions lasted from 1 week to 1 year. No controlled trials with children or adolescents were identified.

The nine studies varied in the amount of face‐to‐face counseling involved. Two studies of medium‐intensity interventions evaluated multiple face‐to‐face sessions of behavioral dietary counseling provided in the primary care setting by a dietitian or nutritionist, or by a primary care physician or nurse practitioner who had received brief training in dietary counseling.34,38 These interventions involved two to three group or individual sessions lasting 30 minutes, with followup visits at 1 and 3 months. Baron et al. reported an 84 percent patient recruitment/participation rate.38

Seven studies involved little or no face‐to‐face counseling and placed greater emphasis on patient self‐help materials, manuals, and varied forms of interactive health communication. Two were studies of low‐intensity interventions that combined brief (<5 minutes) face‐to‐face counseling sessions with a primary care physician or nurse with self‐help materials.9,15 Three others were studies of low‐intensity interventions that relied either on mailed self‐help materials27,36 or on health behavior change messages delivered via an automated computer‐based voice system.29 Campbell et al.27 found significantly greater benefits from tailored than non‐tailored self‐help materials; Lutz et al.36 did not. The remaining two were medium‐intensity interventions that combined a computer‐generated personalized letter and motivational phone call(s) from a trained health educator with a series of self‐help mailings and newsletters.11,28 Patient recruitment and participation in this second group of studies ranged from 16 percent36 to 80 percent,27 with most in the 40 percent to 70 percent range.

These studies in unselected populations produced mostly small (n = 9) and medium (n = 8) as opposed to large (n = 3) improvements in self‐reported dietary behaviors, most of which were statistically significant. Most studies followed patients for 6 months or less post‐intervention; four followed patients for as long as 12 months.11,15,34,38 Only two of them assessed impacts on intermediate biological endpoints (e.g., serum cholesterol, weight, or BMI), of which none reported significant treatment effects.15,38 No studies examined adverse treatment effects.

The USPSTF also reviewed two additional studies that enrolled predominantly healthy premenopausal women, a large proportion of whom were overweight or obese. These studies employed high‐intensity interventions involving multiple dietitian‐led individual14 or group35 counseling sessions. One intervention extended over a 6‐month period and aimed at increasing fruit and vegetable intake14; the other extended over a 5‐year period and focused on dietary fat reduction. Both trials reported large treatment effects in self‐reported dietary behavior at 6‐month post‐intervention followup, and both reported favorable changes in biological risk factors or markers. However, participants in these studies were highly selected and motivated volunteers. The USPSTF concluded that results could not be generalized to more representative primary care populations.

Effectiveness of Intensive Counseling in Patients at Risk for Chronic Disease

The USPSTF found 10 fair‐to‐good quality randomized controlled trials that tested whether medium‐ to high‐intensity interventions delivered in primary care or other clinical settings led to improved dietary outcomes among adults who were identified as being at increased risk for diet‐related chronic disease.10,16,17,2326,3033,37 For two of these trials, two research reports for each were reviewed.1617,3031 No controlled trials with children or adolescents at risk for chronic disease were identified that reported dietary outcomes.

The interventions involved a two‐step assessment: screening to identify a patient's risk status using chart audit/clinical exam/laboratory testing to screen for hyperlipidemia, hypertension, family history of heart disease or breast cancer, overweight, obesity, smoking status, and sedentary lifestyle, followed by assessment of dietary practices using a variety of dietary assessment tools and protocols (e.g., food frequency questionnaires, 3‐4‐day food records, and brief dietary assessment instruments). Hyperlipidemia was included as a risk factor in most of these studies. Four trials addressed diet along with physical activity and/or smoking.2326

Most of the trials tested multi‐session group or individual counseling that combined nutrition education with behaviorally‐oriented counseling. Most studies focused on reducing saturated fat and/or total fat intake; two of these studies also targeted fiber or fruit and vegetable intake,23,24 and one focused on increasing fruit and vegetable intake only.37 Most studies also reported intermediate health outcomes, such as serum lipid levels, blood pressure, weight, and/or BMI. Followup in most studies (n=6) was 12 months or longer, some as long as 4 to 6 years.2326,3032

Six of the trials took place outside of primary care settings, where counseling was provided by an experienced nutritionist, dietitian, and/or health educator in 8 to 20 sessions over a period ranging from 4 months to 5 to 6 years.10 23,25,30,31,33,37 Four trials took place in primary care settings,16,17,24 ,26,32 where counseling was provided by specially trained primary care physicians or nurses (training ranging from 60 minutes to 3 days) in three to six special sessions supplemented by followup phone calls and/or newsletters, and followup at routine visits over a period of 4 to 18 months. In two primary care‐based studies,16,17,32 behavioral dietary counseling for patients with hyperlipidemia was supplemented, if needed, with lipid‐lowering medication and/or referral to outside counseling by a dietitian. Ockene et al.17 found that implementing office‐level systems supports (prompts, reminders, and counseling algorithms) significantly improved primary care provider adherence to the comprehensive dietary counseling.

In summary, interventions for patients at risk for chronic disease resulted in dietary behavior changes that were small (n=3),16,17,23,24 medium (n=6),10,23,24,26,32,37 and large (n=4),10,25,30,33 most of which were statistically significant. The magnitude and duration of these changes were greater with higher intensity interventions than with interventions of lower‐intensity. More than one‐half of these studies found that self‐reported dietary changes were accompanied by significant improvements in serum lipids, weight, or BMI.10,23,24,3032 These findings help corroborate patients' self‐reported dietary changes and confirm the overall health benefits of the observed changes in diet.

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