The Mediterranean diet ranked No. 1 on U.S. News & World Report's list of the Best Diets for 2021, topping the publication's rankings for the fourth straight year.

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How US News picks the best diets

For the Best Diets 2021 ranking, U.S. News reporters and editors "winnow[ed] potential additions" to the rankings and then used government reports, medical journals, and other resources to create profiles for the 39 diets that made the final list. Each profile explains:

• How the diet works;
• Whether the diet lives up to its claims;
• Possible health risks associated with following the diet; and
• What it's like to live on the diet.

A panel of nutrition, diet, obesity, and food psychology experts then reviewed each diet profile and rated the diets on seven criteria:

• Potential for short-term weight loss;
• Potential for long-term weight loss;
• Ease of compliance;
• Nutritional completeness;
• Potential to prevent heart disease;
• Potential to prevent diabetes or serve as a maintenance diet for diabetics; and
• Risk to health.

Once the panelists rated all of the diets, U.S. News converted those ratings into scores and stars, using a five-point scale—with five being the highest score and one being the lowest score. Based on those scores, U.S. News ranked the diets in nine categories:

• Best Diets Overall;
• Best Commercial Diets;
• Best Weight-Loss Diets;
• Best Diabetes Diets;
• Best Heart-Healthy Diets;
• Best Diets for Healthy Eating;
• Easiest Diets to Follow;
• Best Plant-Based Diets; and
• Best Fast Weight-Loss Diets.

Best Overall

The diets that rounded out the top five on the Best Overall list are:

• The Mediterranean Diet, which ranked No. 1 for the fourth consecutive year. According to research, the diet—which is inspired by the observation that people in the Mediterranean live longer, healthier lives—can prevent chronic diseases and increase longevity, U.S. News reports. The diet is low in sugar, red meat, and saturated fats, but high in vegetables, nuts, and fruits.

   

• The Dietary Approaches to Stop Hypertension (DASH) Diet, which tied for No. 2 this year. The DASH Diet combats and prevents high blood pressure and diabetes. Expert panelists ranked the diet highly for its nutritional completeness and ability to support heart health.

   

• The Flexitarian Diet, which also tied at No. 2. The diet is designed to promote weight loss, overall health, and longevity by having people eat mostly—but not completely—vegetarian. The diet emphasizes fruits, vegetables, and whole grains, and is considered easy to follow, making it a "very reasonable, sound, healthy eating plan" that is supported by research, according to the expert panelists.

   

• The WW (Weight Watchers) Diet, which ranks at No. 4 on the overall list, is tied with the flexitarian diet as the best diet for weight loss. According to U.S. News, the myWW program uses WW's SmartPoints system, which assigns point values to foods and beverages based on their nutritional values, "and leverages details about food preferences and lifestyle to match each member to one of three comprehensive ways to follow the program."

   

• The Mayo Clinic Diet, which tied with three other diets at No. 5. On the Mayo Clinic Diet, people follow a "unique food pyramid" that emphasizes fruits, vegetables, and whole grains. It is also one of the best diets for diabetes, according to the panelists.

   

• The Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) Diet, which also tied at No. 5. The diet was created to prevent cognitive decline and promote brain health by increasing the intake of leafy greens, berries, and nuts.

   

• The Therapeutic Lifestyle Changes (TLC) Diet also comes in at No. 5. The diet was created by NIH's National Cholesterol Education Program to help people lower their cholesterol through a heart-healthy eating regimen, which includes fruits, breads, cereals, lean meats, pasta, and vegetables. The TLC Diet's guidelines are broad, providing people with plenty of flexibility in terms of what they can eat.

   

• The Volumetrics Diet, the last diet to rank at No. 5. The diet is aimed at weight loss and places an emphasis on low-density foods, which are low in calories but can be consumed in high volume. Previously, U.S. News has described the diet as follows: "Volumetrics is all about getting more mileage out of what you eat."

Overall, the expert panelists recommended "well-balanced," non-restrictive diets that are sustainable over a lifetime. For instance, "lifestyle diets," such as the MIND Diet and Mayo Clinic Diet, are healthier and more sustainable than diets that stress weight loss, such as Atkins or the Ketogenic diet, according to the panelists.

Top diets across all categories

The No. 1 diets in U.S. News' other Best Diet categories were:

• The Mediterranean Diet, which ranked as No. 1 on its own or tied for the No. 1 spot on the Best Diets for Healthy Eating, Easiest Diets to Follow, Best Diets for Diabetes, Best Heart-Healthy Diets, and Best Plant-Based Diets lists;

   

• The WW Diet, which ranked as No. 1 on the Best Commercial Diets list and tied for No. 1 on the Best Weight-Loss Diets list;

   

• The Flexitarian Diet, which tied for No. 1 on the Best Weight-Loss Diets, Best Diets for Diabetes, and Best Plant-Based Diets lists;

   

• The DASH Diet, which tied for No. 1 on the Best Diets for Healthy Eating and Best Heart-Healthy Diets lists;

   

• The HMR Diet, which ranked as No. 1 on the Best Fast Weight-Loss Diets list; and

   

• The Ornish Diet, which tied for No. 1 on the Best Heart-Healthy Diets list ("Best Diets," U.S. News & World Report, 1/4; U.S. News & World Report release, 1/4; U.S. News & World Report methodology, 1/4).