What evidence indicates who should give dietary advice to reduce cardiovascular risk? A systematic review of randomised controlled trials addresses this issue.9,10
This systematic review aimed to assess how effective dietary advice provided by a dietitian was, compared with such advice provided by other health professionals and self-help resources, in terms of reducing total serum cholesterol in adults. The reviewers electronically searched the Cochrane Library, MEDLINE, EMBASE, CINAHL, Human Nutrition, the Science Citation Index, and the Social Sciences Index. They also hand-searched conference proceedings and contacted experts to find all of the randomised controlled trials through 1999. Randomised controlled trials that compared the effects of dieticians' advice on serum cholesterol levels with the effects of advice by other health professionals or self-help packages were selected. Decisions on inclusion were duplicated by two independent reviewers and disagreements were resolved by discussion or by a third reviewer. Two reviewers independently extracted the data from included studies and assessed trial quality.
Eleven relevant randomised controlled trials (of twelve comparisons) were found and included in the review. Four studies compared advice from dietitians with advice from doctors, one study compared advice from dietitians with advice from nurses, and seven studies compared advice from dietitians with self-help resources.
These studies were carried out in the U.K., the U.S., and Australia in a variety of settings including general practices, workplaces, and clinics. Some participants had heart disease at baseline; others had slightly or distinctly raised serum cholesterol; and some had risk factors for diabetes. Duration of studies varied from 6 to 104 weeks, and data were used only for participants who did not take or had stopped taking lipid lowering medications (so that the outcomes were not biased by the effects of these medications in some groups). Outcome measures in the trials included total serum cholesterol in all studies, along with low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, blood pressure, weight, and patient satisfaction in one or more studies. Participants seen by dietitians tended to be seen more frequently or for longer than those seen by doctors and took part in group sessions and/or individual consultations. Self-help resources were usually simple leaflets.
The quality of included studies was variable, but none reported randomisation procedure in enough detail to enable allocation concealment to be rated as adequate. (Allocation concealment reflects the lack of ability of personnel within the study to accept or reject potential participants according to which intervention they will receive if they enter the trial. It appears to be important in ensuring that two groups entering a study are truly randomised. Where allocation concealment is adequate, effect sizes tend to be smaller and less biased.11)
Patient follow-up of at least 80% in both groups was achieved for four studies only, but blinded and reliable assessment of blood cholesterol was done for all studies. Most studies ensured that participants in different groups did not meet and compare notes on their treatments (this is termed adequate protection against contamination). Several studies revealed significantly different cholesterol levels at baseline between the groups (in four studies the baseline cholesterol levels were higher in the non-dietitian group, whereas in one study the levels were higher in the dietitian group). This is important because it is easier to achieve a fall in cholesterol by starting from a higher baseline. Overall, two studies met five of the six quality criteria, five met four criteria, and four met only two criteria. Studies comparing dietetic input with doctors' advice were of higher quality overall than studies comparing dietetic input with self-help resources.
Meta-analysis (statistically combining the results of all the relevant studies) showed significantly greater falls in total serum cholesterol in participants advised by dietitians instead of doctors (of 0.25 mmol/L, 95% confidence interval [CI] 0.12 to 0.37 mmol/L). This difference was greater in shorter-term studies and declined over time.
However, dieticians' advice did not produce significantly greater falls in total serum cholesterol than self-help resources (greater falls by dietitians of 0.10 mmol/L, 95% CI -0.03 to 0.22 mmol/L) or nurses' advice (greater falls by nurses of 0.08 mmol/L, 95% CI -0.11 to 0.27 mmol/L). Meta-analyses on HDL cholesterol, LDL cholesterol, systolic and diastolic blood pressure, and body weight showed significantly greater falls only in HDL cholesterol when advice was provided by a dietitian (-0.06 mmol/L, 95% CI -0.01 to -0.11) instead of a nurse.
In conclusion, the studies included were not of good quality and analyses were based on limited numbers of trials (and participants). However, the evidence suggests that dietary advice from a dietitian is more effective for lowering total serum cholesterol than is advice from a doctor, but may not be more effective than advice provided by trained nurses or self-help materials.
More high-quality trials would be useful to help elucidate longer-term results, the effects of contact time (the period over which contact takes place), the effects of training other health professionals, the settings that are most effective, and the effects of offering other lifestyle advice in addition to dietary advice. The review set out to address all these issues, but was unable to do so because of the shortage of sizeable trials.
Further relevant studies have been published since 1999 and the Cochrane Review will be updated to include these studies in the near future. Access the Cochrane Library (refer to Section 1.6) to see the latest version of the review. These additional studies may begin to further elucidate the effectiveness of different health professionals and self-help resources and unravel issues such as quantity, type, and frequency of dietary advice required to maintain gains and combat risk factors.
Several randomised controlled trials address the issue of whether dietetic consultation adds anything to a standard consultation with a doctor. Such studies are not included in the systematic review discussed above but are useful because dietary advice is often provided routinely by physicians and it is worth understanding whether additional time spent with a dietitian adds enough to be worth arranging and funding.
A trial by Henkin et al12 randomised 70 hypercholesterolemic patients to dietary counseling by a physician only and 66 to counseling by a physician and a dietitian. The physician sessions were 30 minutes long and included reevaluation of cardiovascular risk factors, a brief physical examination, and counseling on smoking cessation, physical activity, weight control, and the Step I diet. Those receiving the additional time to discuss dietetic issues were offered 2 to 4 individual counseling sessions within 3 months (as needed), the use of food diaries, and Step II advice where appropriate. After 3 months, some participants in the physician-only group were given dietetic appointments if their LDL cholesterol levels were not ideal. Some participants in the dietitian-plus-physician group moved on to lipid lowering medications.
At 3 months, the mean fall in total serum cholesterol levels was 5 mmol/L in the physician-only group and 9 mmol/L in the dietitian-plus-physician group (a significant difference of 4 mmol/L, 95% CI 1 to 7). LDL cholesterol also fell significantly more in the dietitian-plus-physician group (by 5 mmol/L, 95% CI 1 to 9 mmol/L).
A similar study by Delahanty13 enrolled 45 participants with hyperlipidemia (not on lipid lowering medication) for primary care physician advice (usual care), and 45 participants for primary care physician advice plus dietetic intervention (based on an NCEP (National Cholesterol Education Program) cholesterol lowering protocol involving 2 to 3 visits in the first 3 months, plus an additional 2 to 3 visits within 6 months if lipids were not in the target range at 3 months). Total serum cholesterol levels dropped from 6.16 to 6.03 mmol/L at 6 months in the usual care group, and from 6.19 to 5.77 mmol/L at 6 months in the dietetic-plus-physician group (a significant difference). LDL cholesterol fell from 4.24 to 4.13 mmol/L in the usual care group compared with 4.29 to 3.98 mmol/L at 6 months in the dietetic-plus-physician group (not a significant difference). No significant differences in HDL cholesterol, triglycerides, or reported activity between the groups were noted at 6 months, but weight fell more in the dietetic-plus-physician group (usual care baseline 83.2 kg remained at 83.2 kg at 6 months; the dietetic-plus-physician group baseline 79.6 kg decreased to 77.7 kg at 6 months).
This study also assessed cost effectiveness of additional dietetic treatment and found that the additional cost of this treatment totaled $217 per participant to achieve a 6% reduction in total cholesterol and $98 per participant to sustain the reduction. Overall this was a cost of $36 per 1% decrease in total cholesterol and LDL levels.
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