Re: Comparison of seven popular structured dietary programmes and risk of mortality and major cardiovascular events in patients at increased cardiovascular risk: systematic review and network meta-analysis

Dear Editor,

We appreciate the responses by Hoffman and Eckert.

Hoffman argues that virgin olive oil has unique benefits as a monounsaturated fat source within a Mediterranean diet. Our review was not focused on assessing this question (1). Consistent with other systematic reviews, we did not limit our definition of Mediterranean diet by requiring virgin olive oil as a component (2,3). If good evidence exists to suggest virgin olive oil is potentially an effect modifier, future systematic reviews that aim to update the best available evidence on dietary programmes for major cardiovascular outcomes should conduct a priori subgroup analysis of trials with and without virgin olive oil provisions, including subgroups addressing olive oil adherence.

Eckert contends that the presence of co-interventions in our trial threatens our conclusions. We believe this criticism misunderstands our paper. The objective of our paper was to compare “the relative efficacy of structured named diet and health behaviour programmes (dietary programmes)” that could include exercise, psychosocial or behavioural support, smoking cessation interventions and drug treatments. In other words, the interventions that our review assessed were not necessarily dietary interventions alone. If we had limited our review to interventions that only involved diets, we would have been unable to include popular structured programmes that include exercise and smoking cessation, such as the Ornish programme. We explicitly state in our discussion section: “our results apply primarily to dietary programmes as a whole, which include exercise and psychosocial support cointerventions, rather than to diets alone.” To explore if co-interventions were effect modifiers, we reported that “our network meta-regression did not find any substantial difference in odds ratios when controlling for the presence of cointerventions (exercise, psychosocial support such as stress management, smoking cessation, and drug treatment).” Further, we conducted sensitivity analyses excluding trials with treatment arms including either smoking cessation or drug treatment co-interventions. Results revealed similar findings to our main analysis; however, loss of statistical significance was observed for low fat dietary programmes. For Mediterranean dietary programmes, while still statistically significant, the sensitivity analysis results were based on high risk of bias trials. This reduced our certainty in the specific dietary programme components that drove the risk reductions, and so we rated down for indirectness. Our paper, then, already incorporates Eckert’s suggestion to downgrade for co-intervention imbalance.

Giorgio Karam, Max Rady College of Medicine, University of Manitoba, Canada
Bradley C. Johnston, Department of Nutrition, Texas A&M University, United States

References:
1. Karam G, Agarwal A, Sadeghirad B, et al. Comparison of seven popular structured dietary programmes and risk of mortality and major cardiovascular events in patients at increased cardiovascular risk: systematic review and network meta-analysis. BMJ 2023, 380, e072003.
2. Ge L, Sadeghirad B, Ball GDC, et al. Comparison of dietary macronutrient patterns of 14 popular named dietary programmes for weight and cardiovascular risk factor reduction in adults: systematic review and network meta-analysis of randomised trials. BMJ 2020;369:m696. doi:10.1136/bmj.m696. pmid:32238384
3. Rees K, Takeda A, Martin N, et al. Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev2019;3:CD009825. doi:10.1002/14651858.CD009825.pub3. pmid:30864165