Control of bias in dietary trial to prevent coronary recurrences: The Lyon diet heart study

Abstract

Background and Objectives: A major limitation of dietary trials is that double blind design is not feasible. These trials are therefore prone to biases. The Lyon diet heart study is a single-blind secondary prevention trial to test the hypothesis that a Mediterranean-type of diet may prevent recurrences after a ®rst myocardial infarction. A surprising 73% reduction of the risk of new major cardiac events was observed in the experimental group. For this reason, it is important to describe the methods used in the trial. We now report our techniques to randomize the patients, to change their diet and to control for possible bias, in particular any investigator or attending physician bias. Design: In this dietary trial, a speci®c design was used to recruit and randomize the patients without informing them and their physicians that they were participating in a comparative trial. The attending physician bias was evaluated by studying drug usage and the investigator bias by constructing a questionnaire from which speci®c scores were used to evaluate (1) how the patients appreciated their participation in the study and (2) whether this participation resulted in signi®cant changes in their way of living. Subjects: 605 survivors of a ®rst myocardial infarction were randomized into either a control or a Mediterranean group. Results: The two randomized groups were similar for all the variables of prognosis. Drug usage was not signi®cantly different between groups, suggesting that there was no major attending physician bias. Analyses of the appreciation scores and of the change score did not detect any signi®cant investigator bias. Conclusions: Although the study cannot be completely shielded from minor biases, the data presented here provide evidence that the dietary modi®cations per se were protective, not other (including psychosocial) changes resulting from the participation to the trial. Descriptors: dietary trial; control of biases; coronary heart disease; Mediterranean diet; attending physician.

Relationships among diet, physical activity and other lifestyle factors and debilitating diseases in the elderly

“…A modest intake of oily ®sh (or ®sh oil capsules) resulted in a 29% reduction in total mortality during the ®rst 2 y after a myocardial infarction (without any change in total plasma cholesterol concentration) (Burr et al, 1989), while no bene®t was observed from conventional high ®bre and low saturated fat diets. The Mediterranean diet, high in antioxidants, vitamins, oleic acid and n-3 fatty acids, resulted in a 73% reduction in major cardiac events in patients recovering from a myocardial infarction (De Lorgeril et al, 1997). In practice it is likely that advice to adopt this type of diet might be more acceptable than the promotion of low-fat and low-cholesterol diets (Conway, 1998).…”

Mediterranean Dietary Pattern in a Randomized Trial

“…7,8 In the absence of major bias 9 and in view of the good compliance with the experimental diet and the lack of between-group contamination, [7][8][9] the Lyon trial may offer the opportunity to examine the effect of this dietary pattern on overall survival and newly diagnosed cancer rate, although sample size and duration of follow-up were not calculated specifically for this purpose. Given the number of cancers observed in a similar middle-aged CHD population 10 and the Lyon study sample size, the expected number of cancers in this study was calculated to be approximately 40 during a follow-up of 4 years.…”

“…Patients in the experimental group and their families were seen by the dietitian at the randomization visit, 2 months later, and then once a year. The specific techniques used to instruct these patients have been previously described, 9 and compliance with the dietary intervention was checked by a dietary survey (including a 24-hour recallandafoodfrequencyquestionnaireateachvisit)andanalyses of plasma fatty acids. 21 Patients in the control group were expected to follow the dietary advice given by their attending physicians (not involved in the study) and close to the step 1 diet of the American Heart Association (characterized as 30% of total energy as fats, 10% saturated, 10% monounsaturated, and 10% polyunsaturated, and cholesterol intake lower than 300 mg/d).…”

Cocoa, Blood Pressure, and Vascular Function

“…Polyphenol-rich foods, such as fruit, vegetables, wine, olive oil, and cocoa, are able to reduce cardiovascular risk and prevent cardiovascular events and death (3)(4)(5)115). Among them, cocoa beans have always been of particular interest, as they are one of the richest polyphenol sources.…”

“…A nutraceutical approach has been proposed to counteract the increasing burden of CVD. The consumption of polyphenol-rich foods has been related to a lower risk of cardiovascular events (cardiovascular mortality, myocardial infarction, and stroke) both in the general population and in patients with cardiovascular risk factors in several interventional and epidemiological trials (2)(3)(4)(5). Polyphenols are believed to be largely responsible for this protective role.…”