Evidence supports Mediterranean and low-fat diets for reducing mortality and heart attack risks in high-risk patients

By Dr. Liji Thomas, MDApr 2 2023Reviewed by Danielle Ellis, B.Sc.

Cardiovascular disease is one of the leading causes of death in the world today. Its connection with an unhealthy lifestyle, particularly unhealthy dietary patterns, is well-known. In fact, scientists estimate that about one in five deaths among adults occur because of poor diet patterns, contributing to one in seven disability-adjusted life years (DALYs).

A multiplicity of diets and other interventions are available to reduce the risk of cardiovascular events, including death, in those at high risk for cardiovascular disease. However, there is little data on how to choose the best dietary intervention among them.

A new research paper performed a cross-analysis of a spectrum of dietary programs, from those requiring little intervention to detailed, multifaceted programs, examining the mortality and major cardiovascular events over a follow-up period.

Study: 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. Image Credit: Margarita Steshnikova / Shutterstock

Introduction

Earlier comparisons of dietary programs have depended on proxy outcomes or used poor-quality evidence based on non-randomized studies. The current study, published in The British Medical Journal, used network meta-analyses to perform head-to-head comparisons of different interventions using both direct and indirect evidence.

The former compares two or more active interventions, while the latter compares active vs. non-active control groups. This allowed the investigators to directly compare the effects of interventions for which direct comparisons were not available in the literature. They reviewed and analyzed all eligible randomized controlled trials based on structured dietary interventions aimed at reducing mortality and major cardiovascular outcomes.

The study included 40 trials, with a total of over 35,000 participants, encompassing seven distinct types of dietary plans. These comprised low-fat (such as the National Cholesterol Education Program diets), Mediterranean, very low-fat, modified fat, combined low-fat and low-sodium, Ornish, and Pritikin programs.

These were compared with minimal intervention programs, ranging from not receiving dietary advice, usual care, or dietary brochures to very infrequent brief dietary advice without follow-up or reinforcement.

What does the study show?

The analysis shows that among all available dietary programs, the Mediterranean diet provided better results in multiple parameters compared to minimal interventions such as diet handouts or brochures. The risk of death from any cause dropped by ~30%, with the number of deaths per 1,000 decreasing by 17 over five years.

Among patients at intermediate risk, death from cardiovascular disease was reduced by over half, at 13 fewer deaths per 1,000 over five years. The risk of stroke and non-fatal myocardial infarction also fell by a third and a half, respectively, with 7 and 17 fewer events per 1,000 over five years in the intermediate-risk group.

Among high-risk patients, the risk of death from any cause fell further, with 36 fewer deaths per 1,000. Stroke rates fell by 16 per 1,000 in this group, but non-fatal heart attacks by 42 per 1,000.

Low-fat programs also showed better risk reduction compared to minimal intervention programs. The risk of death from any cause was reduced by 16%, with nine fewer deaths per 1,000 over five years among those at intermediate risk and 20 fewer deaths per 1,000 among high-risk patients. In addition, non-fatal heart attacks were reduced by ~20% over the same period, with -7 and -18 deaths per 1,000 in intermediate- and high-risk groups, respectively.

Unplanned interventions for cardiovascular disease were reduced in the low-fat programs by ~45%, though the evidence is of low certainty.

The Mediterranean and low-fat diets appeared to have comparable effects on all-cause death rates and non-fatal heart attack rates among intermediate-risk patients. The most significant fall in the number of events was observed among patients at high risk in both situations. The changes occurred irrespective of whether exercise or other interventions were added in or not.

The other five plans did not show any better results than minimal interventions, though the evidence was of low to moderate certainty in most cases.

What are the implications?

“Our results are best understood as reflecting expected benefits given average adherence to a dietary programme.”

The findings allow moderate certainty that the Mediterranean and low-fat dietary programs reduce all-cause mortality and non-fatal heart attacks, and the former also reduces stroke risk.