A recent review article in the New England Journal of Medicine outlines the potential health benefits, beyond weight loss, of “the most widely recognized, scientifically explored, and broadly promoted diets,” including a variety of vegetarian, low-fat, and carbohydrate-restricted diets.

The most extensively studied diet is the Mediterranean diet, which consists mainly of plant products including nuts, seeds, fruits, and vegetables; moderate amounts of dairy; wine; fish and poultry; and low amounts of red meat. A meta-analysis that included data from nearly 13 million people showed adherence to the diet reduced the incidence of all-cause mortality, coronary artery disease, myocardial infarction, cancer, diabetes, and neurodegenerative diseases.

Vegetarian diets take various forms and may be adopted for myriad reasons—ecological, philosophical, religious, or ethical. Generally defined as diets that exclude meat or meat-derived products, this group of diets includes vegan (no animal products), lacto-vegetarian (includes dairy products), ovo-vegetarian (includes eggs), and pescatarian (includes fish). Vegetarian diets have been linked to benefits similar to the Mediterranean diet; however, more restrictive forms of vegetarian diets have been associated with vitamin deficiencies.

Low-fat diets became popular in the 1980s and are typically defined as diets that include less than 30% of caloric intake from lipids. The Women’s Health Initiative Dietary Modification Trial showed a modest reduction in breast cancer mortality with a low-fat diet. Other studies have established benefits on cholesterol levels and blood pressure, and reduced risk of myocardial infarction and heart disease.

Diets that consist of 50 to 150 grams of carbohydrates a day are considered low carbohydrate. These types of diets have demonstrated weight loss comparable to other types of diets. A ketogenic version, in which daily carbohydrate intake is limited to 20 to 50 grams, have been shown to improve cardiovascular risk factors. The authors note that interest is growing in studying the effects of a ketogenic diet on schizophrenia, Alzheimer’s disease, and cognitive function. Although the mechanisms aren’t clear, ketogenic diets have been shown to reduce seizures.

The MIND (Mediterranean–DASH [Dietary Approaches to Stop Hypertension] Intervention for Neurodegenerative Delay) diet was developed specifically to address cognitive function. Plant products make up the majority of this diet, especially berries and leafy green vegetables. Saturated lipids and red meat are restricted and olive oil is the primary oil. Low amounts of fish and chicken are also recommended. The MIND diet has demonstrated a positive effect on cognitive outcomes and is currently being studied in a randomized clinical trial.

The systematic study of diets poses many challenges including agreed-upon definitions of the various diets, patient adherence, a lack of standardized measures, ethnic differences, and a multitude of confounding variables. But given the potential health benefits—both physical and mental—of plant-based diets with modest fat intake, the authors conclude, “Advice on healthy eating should be incorporated into clinical practice and taught in medical curricula, and health care professionals should propose variations of plant-based diets…”

Read the review

References: Yannakoulia M, Scarmeas N. Diets. N Engl J Med. 2024;390(22):2098-2106. doi:10.1056/NEJMra2211889