The  American Heart Association (AHA)  rated  10 types of popular diets based on how well they align with AHA's dietary guidance, with the Dietary Approaches to Stop Hypertension (DASH) diet receiving a perfect score.

Methodology

AHA evaluated each diet against nine of the 10 features in AHA's guidance  for heart-healthy eating, excluding "eating to achieve a proper energy balance to maintain a healthy weight," as this can be influenced by many factors other than dietary choices.

Features that fully met AHA's guidelines were given one point, while features that mostly met the guidelines received 0.75 points, and partially meeting AHA's guidance received 0.5 points. If a feature of the diet did not meet AHA's guidance at all, it received zero points. Scores were totaled and adjusted to receive a rating between zero and 100.

AHA did not review commercial dietary programs like  Weight Watchers and  Noom, nor did it review diets intended to be followed for less than 12 weeks, dietary practices like intermittent fasting or time-restricted eating, or diets designed to manage non-cardiovascular conditions.

AHA rated and reviewed 10 categories of diets, including:

• DASH-style, including the DASH, Nordic, and Baltic diets
• Mediterranean-style, including the Mediterranean diet
• Vegetarian/Pescatarian, a plant-based diet that includes fish
• Vegetarian/Ovo/Lacto, a plant-based diet that includes eggs, dairy, or both
• Vegetarian/Vegan, a plant-based diet including no animal byproducts
• Low-fat, including the Volumetrics eating plan and the Therapeutic Lifestyle Change plan
• Very low-fat, including the Ornish, Esselstyn, Pritikin, McDougal, and Physicians Committee for Responsible Medicine diets.
• Low-carbohydrate, including the South Beach, Zone, and low glycemic index diets
• Paleolithic, including the Paleo diet
• Very low-carbohydrate/ketogenic, including Atkins, ketogenic, and Well-Formulated Ketogenic diets.

The best (and worst) diets for your heart

AHA divided the diets into four tiers based on how well they scored.

Tier 1: Scores higher than 85

The DASH-style diet received a perfect score from AHA thanks to its emphasis on low amounts of salt, added sugar, alcohol, tropical oils, and processed foods and high amounts of non-starchy vegetables, fruits, whole grains, and legumes. Protein typically comes from plant sources as well as fish, seafood, lean poultry and meats, and low-fat or fat-free dairy products.

The Mediterranean-style diets were also highly rated. However, since the diets don't specifically address added salt and include moderate alcohol consumption, it received a slightly lower score.

The majority of vegetarian style diets, including pescatarian and vegetarian eating plans including eggs, dairy, or both, also received high scores.

Tier 2: Scores between 75-85

Vegan and low-fat diets emphasize vegetables, fruits, whole grains, legumes, and nuts and limiting alcohol and added sugars. However, these diets also make them difficult to follow long-term or when eating out, AHA said. Vegan diets can also increase a person's risk of developing a vitamin B-12 deficiency, which could lead to anemia.

Low-fat diets also tend to treat all fats the same, while AHA's guidance recommends replacing saturated fats with healthier fats like mono- and polyunsaturated fats. Low-fat diets may also lead people to over-consume sources of carbohydrates that are less healthy, including carbohydrates with added sugars and refined grains.

Tier 3: Scores between 55-74

This tier included very low-fat and low-carb diets, both of which restrict food groups emphasized in AHA's guidance.

Very low-fat diets restrict nuts and healthy non-tropical plant oils, which could also result in vitamin B-12 deficiencies, as well as deficiencies of essential fatty acids and protein, which could lead to anemia and muscle weakness, AHA said.

Meanwhile, low-carb diets restrict fruits, grains, and legumes. In addition, restricting carbohydrates can lead diet followers to decrease their consumption of fiber while increasing their saturated fat consumption through meats and foods from animal sources.

Tier 4: Scores less than 55

This tier included Paleolithic and very low-carb/Ketogenic diets. Very low-carb diets received points for their emphasis on consuming non-starchy vegetables, nuts, and fish and minimizing the consumption of alcohol and added sugars. However, while studies have found improvements in body weight and blood sugar following these diets, after a year, improvements were found to be no different than less restrictive diets, AHA said.

These diets also restrict consumption of fruits, whole grains, and legumes, which could reduce a person's fiber intake. The diets are also high in fat without restricting saturated fats, which, when combined with low levels of fiber, have been linked to cardiovascular disease. (American Heart Association release, 4/27)