April 19, 2023
BMJ : British Medical Journal
TAKE-HOME MESSAGE
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- This large meta-analysis examined randomised controlled trials to assess the effects of seven popular diets (low-fat; Mediterranean; very low–fat; modified fat diet with a higher proportion of polyunsaturated fats; combined low-fat and low-sodium; Ornish; and Pritikin) on mortality. The results showed mortality benefits with the Mediterranean and low-fat diets only, with the Mediterranean diet having the additional benefit of being protective against stroke (low-fat diets also protected against all-cause mortality).
- These results show further evidence of the benefits of the Mediterranean diet in mortality, stroke, and cardiovascular disease prevention. Low-fat diets had fewer benefits, whereas the popular Ornish and Pritikin diets had no observable benefits.
Abstract
OBJECTIVE
To determine the relative efficacy of structured named diet and health behaviour programmes (dietary programmes) for prevention of mortality and major cardiovascular events in patients at increased risk of cardiovascular disease.
DESIGN
Systematic review and network meta-analysis of randomised controlled trials.
DATA SOURCES
AMED (Allied and Complementary Medicine Database), CENTRAL (Cochrane Central Register of Controlled Trials), Embase, Medline, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and ClinicalTrials.gov were searched up to September 2021.
STUDY SELECTION
Randomised trials of patients at increased risk of cardiovascular disease that compared dietary programmes with minimal intervention (eg, healthy diet brochure) or alternative programmes with at least nine months of follow-up and reporting on mortality or major cardiovascular events (such as stroke or non-fatal myocardial infarction). In addition to dietary intervention, dietary programmes could also include exercise, behavioural support, and other secondary interventions such as drug treatment.
OUTCOMES AND MEASURES
All cause mortality, cardiovascular mortality, and individual cardiovascular events (stroke, non-fatal myocardial infarction, and unplanned cardiovascular interventions).
REVIEW METHODS
Pairs of reviewers independently extracted data and assessed risk of bias. A random effects network meta-analysis was performed using a frequentist approach and grading of recommendations assessment, development and evaluation (GRADE) methods to determine the certainty of evidence for each outcome.
RESULTS
40 eligible trials were identified with 35 548 participants across seven named dietary programmes (low fat, 18 studies; Mediterranean, 12; very low fat, 6; modified fat, 4; combined low fat and low sodium, 3; Ornish, 3; Pritikin, 1). At last reported follow-up, based on moderate certainty evidence, Mediterranean dietary programmes proved superior to minimal intervention for the prevention of all cause mortality (odds ratio 0.72, 95% confidence interval 0.56 to 0.92; patients at intermediate risk: risk difference 17 fewer per 1000 followed over five years), cardiovascular mortality (0.55, 0.39 to 0.78; 13 fewer per 1000), stroke (0.65, 0.46 to 0.93; 7 fewer per 1000), and non-fatal myocardial infarction (0.48, 0.36 to 0.65; 17 fewer per 1000). Based on moderate certainty evidence, low fat programmes proved superior to minimal intervention for prevention of all cause mortality (0.84, 0.74 to 0.95; 9 fewer per 1000) and non-fatal myocardial infarction (0.77, 0.61 to 0.96; 7 fewer per 1000). The absolute effects for both dietary programmes were more pronounced for patients at high risk. There were no convincing differences between Mediterranean and low fat programmes for mortality or non-fatal myocardial infarction. The five remaining dietary programmes generally had little or no benefit compared with minimal intervention typically based on low to moderate certainty evidence.
CONCLUSIONS
Moderate certainty evidence shows that programmes promoting Mediterranean and low fat diets, with or without physical activity or other interventions, reduce all cause mortality and non-fatal myocardial infarction in patients with increased cardiovascular risk. Mediterranean programmes are also likely to reduce stroke risk. Generally, other named dietary programmes were not superior to minimal intervention.
SYSTEMATIC REVIEW REGISTRATION
PROSPERO CRD42016047939.
Dietary influence on inflammation and insulin resistance
This network meta-analysis looked at several popular diets and found that the Mediterranean diet had the greatest effect on all-cause mortality, nonfatal myocardial infarction, and stroke in patients with high cardiovascular risk. The low-fat diet also showed benefits for all the above, except stroke.
A plant-forward Mediterranean diet and a low-fat diet reduced inflammation and insulin resistance, two dietary effects, which a study involving 205,852 healthcare professionals followed for 32 years found to have the greatest effect in reducing heart disease, diabetes, and cancer.1
Those patients who had the highest MED score (below) compared with those who had the lowest MED score had a 28% reduced risk of having a primary cardiac event.2
MED score (one point for each, 1–9)
Number 9 (EToH) is controversial. If there is a high risk of cancer, alcohol should be avoided altogether.
A recent story of the week reviewed a paper suggesting that inflammation was a significant unaddressed risk factor in patients on statins. Being on a statin is not enough. We need to also address inflammation.
Shah and colleagues3 quantified those underlying pathophysiologic processes that have the most effect on increasing the risk of a cardiovascular event. They also concluded that inflammation and insulin resistance were at the top.
Most powerful factors affecting CV risk
Both the Mediterranean diet and the low-fat diet reduce inflammation by reducing fat intake. Saturated fat is high in arachidonic acid, which fuels the inflammatory cascade. The Mediterranean diet is high in fiber, which slows the absorption of sugar (glycemic index) and protects against insulin resistance.
A growing nutrition concern that has not been in the literature long enough for a network meta-analysis to evaluate is that of non-nutritive sweeteners. These have been associated with increasing platelet aggregation and insulin resistance.4,5
Health is much more about what we do than what we take. Nutrition and exercise continue to be the most effective, evidence-based interventions in preventing the number one cause of death on the planet. Maybe we should invest more in supporting these interventions in our communities, thereby reducing the need, cost, and risk of polypharmacy.
References