Background: Blood cholesterol level is an important indicator of the risk of developing heart disease. Blood cholesterol can be lowered by making changes in diet. Ideally, dietitians should give dietary advice to patients. Due to practical considerations, often dietary advice is given by other health professionals.
What was the (research) question the reviewers were trying to answer? What is the effectiveness of dietary advice given by dietitians to lower blood cholesterol, compared to that given by other health professionals, or using self-help resources?
What did the reviewers do? The reviewers searched for Randomized Controlled Trials (RCTs) that compared the effects of dietary advice given by dietitians versus other health professionals, or using self-help resources. The main outcome was difference in blood cholesterol levels between dietitian compared with other groups. Twelve studies were with 13 comparisons were included. Four studies compared dietitian with doctor, and seven with self-help resources. One study compared dietitian with nurses; and dietitian with counsellor for body weight.
What did they find? Advice by dietitians was more effective than doctors, but as effective as self-help resources in lowering blood cholesterol levels. There was no evidence to suggest that advice given by dietitians was more effective than that given by nurses (to lower blood cholesterol).
How does one explain these findings?
1. Only RCTs were included in this review. Many of the studies were not of good quality, hence the results must be viewed with caution.
2. When dietary advice was given by a dietitian only, the blood cholesterol levels were lowered by an additional 0.25 mmol/ L (4%) as compared to advice given by a doctor only. The difference is small, but statistically significant. Often, when a large number of subjects are studied, even small differences become statistically significant. This is not unusual. Is 0.25 mmol/ L clinically significant (is the difference big enough to convince a change in patient management)? Probably not.
3. It is not possible to determine whether the lowering of blood cholesterol was solely due to the advice given.
4. The results are valid only for the short to medium term. There is some indication that the effects were inversely proportional to the duration of the study. That is, the shorter the study, the greater the fall in blood cholesterol level. Naturally, one cannot expect similar results over the long term (it is similar to maintaining a diet/ exercise regimen- a few days of enthusiasm may initially cause a big drop in weight, but it is unusual for the enthusiasm to sustain; or for a similar rate of weight loss over the long term)
5. Long term studies are lacking, hence long term effectiveness cannot be estimated from this review.
Bottomline: In the short- medium term, dietary advice given by dietitians may help lower blood cholesterol levels to a greater degree than doctors. However, the difference is not clinically meaningful. Dietary advice given by dietitians was as effective as the use of self-help resources. There is no evidence to suggest that advice given by nurses is less effective than dietitians. Long term effectiveness cannot be determined based on current evidence.