Giving people advice about healthy eating, even in small doses, appears to produce changes in diet that lead to modest improvements in some cardiovascular risk factors, according to a new systematic review of studies.

The review, led by epidemiologist Eric Brunner of University College, London, analyzed 23 studies in which 24,443 healthy people were randomly assigned to receive either dietary advice or no dietary advice.

Brunner and colleagues found that consumption of fruit and vegetables, dietary fiber, fat, and salt showed improvement in the groups that received the advice. Fruit and vegetable intake increased by 1.2 servings per day and dietary fiber intake increased by 7.2 grams per day.

Reviewers also found some improvements in blood pressure, total cholesterol, low-density lipoprotein and high-density lipoprotein blood levels. The effects were noted up to nine months after people received the advice, but it was not possible in these studies to tell if there could be longer-lasting effects.

Dietary advice was associated with a reduction of 0.13 mmol/cholesterol. Advice to reduce salt resulted in a reduction of 2.1 mm/Hg in the systolic pressure (the top number) and 1.6 mm/Hg reduction in diastolic pressure.

These changes may sound small, but they are beneficial, Brunner said. For example, the estimated equivalent of a 5 mm/Hg reduction in diastolic blood pressure, based on other cohort studies, is a 21 percent reduction in coronary heart disease and a 34 percent reduction in stroke, the researchers said.

The review appears in the most recent issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

Other studies have shown that lifestyle intervention can be effective for those at high risk of disease, Brunner said.

“Doctors and other health personnel are highly influential with respect to their patients’ opinions, and our new evidence confirms that contact with primary care staff is an opportunity to help change dietary behavior,” he said. “For healthy adults, repeated brief physician reinforcement of healthy eating messages is likely to be the most effective approach, with the limited time allowance per patient.”

In the studies Brunner reviewed, advice was given in one-on-one sessions, group sessions or through written materials. Trials that also advised about exercise or other lifestyle changes were excluded from the review.

The duration of the dietary advice ranged from one contact once with each participant to studies where participants received up to 50 hours of counseling over four years. The average follow-up period for the trials used in the review was nine months.

There was a larger response to diet advice among participants who were at increased risk for cardiovascular problems or cancer, but benefits were seen for other participants as well. Patients who were at higher risk for developing cancer were more likely to substantially increase their intake of fruits and vegetables.

The review found that, in general, women were more likely than men to reduce dietary fat intake and increase the amount of fruits and vegetables in their diet, but there was no difference between the genders in the total cholesterol levels found.

“This is the first systematic study to show modest evidence for the benefits of physician counseling of diet changes in patients,” said Dawn Wilson, professor of psychology at the University of South Carolina.

How often doctors counsel their patients about diet in their normal clinical practice is not known, Brunner said. “The practice is likely to be highly variable.”

Brunner EJ, et al. Dietary advice for reducing cardiovascular risk (review). The Cochrane Database of Systematic Reviews 2005, Issue 4.