In people who have cardiovascular disease or are at high risk for cardiovascular disease, Mediterranean and low fat diets reduce risk for death

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 Mar 29;380:e072003.

Review question

In people who have cardiovascular disease or are at high risk for cardiovascular disease, how do different types of diets compare for reducing death?

Background

Diet is an important factor for health, and some types of diets are believed to reduce risk for cardiovascular events. It is less clear whether dietary programs can reduce risk for death.

How the review was done

The researchers did a systematic review of studies available up to September 2021. They found 40 randomized controlled trials that included 35,548 people.

The key features of the studies were:

• 31 studies included adults with who had cardiovascular disease, and 9 included adults who did not have cardiovascular disease but had at least two risk factors for cardiovascular disease;
• dietary programs were
• Mediterranean (higher intake of fish, fruit, vegetables, and monosaturated fats such as olive oil);
• low fat (total fat intake 20% to 30% of total calories and saturated fat intake <10% of calories);
•  very low fat (total fat intake 10% to 20% of total calories);
• modified fat (no reduction in total fat intake, but more polyunsaturated fat than saturated fat);
•  combined low fat and low sodium (total fat intake 20% to 30% of total calories, saturated fat intake <10% of calories, and sodium <2.4 g/day);
• Ornish (primarily plant based, with total fat intake <10% of total calories), and;
• Pritikin (total carbohydrate intake 70% to 75%, total protein intake 15% to 20%, and total fat intake 5% to 10% of total calories; fibre intake 40 to 45 g/1000 kilocalories) diets;
• dietary programs were compared with other cardiovascular risk reduction interventions (including other dietary programs, exercise, drug therapy, smoking cessation, and other therapies) or minimal intervention (no dietary advice or very little dietary advice and support);
• the dietary programs lasted for at least 9 months; and
• the effects of the dietary programs on death and/or major cardiovascular events were assessed at less than 1 year to 17 years later.

What the researchers found

Compared with the control group:

• Mediterranean (higher intake of fish, fruit, vegetables, and monosaturated fats such as olive oil) and low fat (total fat intake 20% to 30% of total calories, saturated fat intake <10% of calories) dietary programs reduced risk for death at up to 17 years (moderate quality evidence); and
• very low fat, modified fat, combined low fat and low sodium, Ornish, and Pritikin dietary programs did not reduce death at up to 17 years (very low to moderate certainty evidence).

Conclusion

In people who have cardiovascular disease or are at high risk for cardiovascular disease, Mediterranean and low fat diets reduce risk for death.

Dietary programs vs. control for reducing death in people who have cardiovascular disease or are at high risk for cardiovascular disease*

*Only the dietary interventions that affected death are reported in the Table. The values are based on people with average risk at baseline.

†Dietary programs reported are Mediterranean (higher intake of fish, fruit, vegetables, and monosaturated fats such as olive oil) and low fat (total fat intake 20% to 30% of total calories, saturated fat intake <10% of calories). Very low fat, modified fat, combined low fat and low sodium, Ornish, and Pritikin dietary programs did not reduce death.