Mediterranean, Low-fat Diets May Reduce Death, CV Events in Patients at Increased Risk

Mediterranean and low-fat dietary plans were associated with reduced risk for death and nonfatal myocardial infarction (MI) in persons at intermediate or high cardiovascular (CV) risk, according to a new systematic review and meta-analysis published online March 29 in the BMJ.

The 2 dietary programs, along with 5 other structured, named diet and health behavior plans, were compared with "minimal intervention" for their relative efficacy to prevent mortality and major CV events in patients considered at significant risk.

The investigators report that the other 5 programs—very low fat, modified fat, combined low fat/low sodium, Ornish, and Pritikin dietary patterns—demonstrated little or no benefit related to death and MI when compared with minimal intervention, defined for the study as usual diet or brief dietary advice from a health professional.

The systematic review and meta-analysis, led by Bradley C Johnston, PhD, associate professor of nutrition and of epidemiology and biostatistics at Texas A&M University, identified a total of 40 randomized, controlled trials of patients at increased CV risk that compared dietary programs with minimal intervention with at least 9 months of follow-up and reporting on mortality of major CV events.

The trials comprised 35 548 participants and evaluated Mediterranean (12 trials), low-fat (18 trials), modified fat (6 trials), combined low fat/low sodium (4 trials), Ornish (3 trials) and Pritikin (1 trial) diet programs. The programs could combine exercise, behavioral support, and other secondary interventions with the dietary plan. The median follow-up among the trials was 3 years, according to study results.

Johnston and colleagues report that at the last reported follow-up, and based on moderate certainty evidence, the Mediterranean diet pattern was superior to minimal intervention programs for prevention of:

• All-cause death (OR 0.72; 95% CI, 0.56-0.92; risk difference in patients at intermediate risk, 17 fewer per 1000 patients followed for 5 years)
• CV mortality (OR 0.55; 95% CI, 0.39-0.78; risk difference in patients at intermediate risk, 13 fewer/1000)
• Stroke (OR 0.65; 95% CI, 0.46-0.93; risk difference in patients at intermediate risk, 7 fewer/1000)
• Nonfatal MI (OR 0.48; 95% CI, 0.36-0.65; risk difference in patients at intermediate risk, 17 fewer/1000)

The researchers also found the low-fat dietary patterns superior to minimal intervention (with moderate certainty) for prevention of all-cause mortality (OR 0.84, 95% CI, 0.74-0.95; 9 fewer/1000) and non-fatal MI (OR 0.77; 95% CI, 0.61- 0.96; 7 fewer/1000)

When investigators directly compared the Mediterranean and low-fat dietary programs, they found no differences related to prevention of death or nonfatal MI. They did report, however, that absolute effects of both dietary patterns were more pronounced for patients at high risk for CV death.

Other than “possibly” the combined low-fat/low-sodium programs which showed some convincing evidence of benefit compared to minimal intervention, the 5 others showed none.

Among the study’s limitations the authors note the inability to measure dietary adherence as well as the possibility that some of the net risk reduction may have come from other elements of the specific programs, eg, pharmacotherapy.

The review, the authors write, is the first one of comparative effectiveness of competing structured and named dietary programs. “These findings with data presentations are extremely important for patients who are skeptical about the desirability of diet change,” wrote Johnston and colleagues in conclusion.

Reference: Karam G, Agarawal 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. doi: 10.1136/bmj-2022-072003