"The number of different, popular dietary patterns has proliferated in recent years, and the amount of misinformation about them on social media has reached critical levels," said AHA’s Christopher D. Gardner, Rehnborg Farquhar Professor of Medicine at Stanford University.

"We often find that people don't fully understand popular eating patterns and aren't following them as intended," he added. "When that is the case, it is challenging to determine the effect of the 'diet as intended' and distinguish that from the 'diet as followed.' Two research findings that seem contradictory may merely reflect that there was high adherence in following the diet in one study and low adherence in the other."

Experts assessed the diets against nine of the 10 recommendations the AHA provides to eat for heart health. Those guidelines include well-acknowledged aspects of healthy eating: consuming a wide range of fruit and vegetables, whole grains over refined grains, healthy sources of protein such as from plants, minimizing sugar and salt, and limiting alcohol, among others.

The diets were then rated on a scale of one to 100 and divided into four tiers.

The scorecard was as follows: DASH eating plan (100), pescatarian diet (92), Mediterranean diet (89), vegetarian diet (86), vegan diet (78), low-fat diet (78), very low-fat diet (72), low-carb diet (64), paleolithic diet (53) and very low-carb/ketogenic diet (31).

DASH (Dietary Approaches to Stop Hypertension) came out on top, due to it being low in salt, added sugar, alcohol and processed foods, while high in non-starchy vegetables, fruits, whole grains and legumes. Proteins mostly come from plant sources, such as legumes, beans or nuts, and seafood.

The Mediterranean diet ranked lower than DASH because of its moderate alcohol consumption and no guidelines as to salt intake. Pescatarian and vegetarian eating patterns also made the top-tier grade.

Some patterns, such as a vegan diet, lost points for there being some health risks such as vitamin B-12 deficiency, while very low-fat and low-carb diets were third-tier plans due to their respective restrictions for things like nuts, healthy plant oils, fruits, grains and legumes.

Rounding out the bottom tier were paleo and keto diets, which received a poor rank both due to nutrient restriction and sustainability.

"[These] are highly restrictive and difficult for most people to stick with long-term,” Gardner said. “While there will likely be short-term benefits and substantial weight loss, it isn't sustainable. A diet that's effective at helping an individual maintain weight-loss goals, from a practical perspective, needs to be sustainable."

Researchers did not assess commercial dietary programs or eating patterns such as intermittent fasting, or any plans that addressed non-cardiovascular health issues.

While intended to be a simpler, flexible guide for improved heart health, the AHA hopes it will also be handy for healthcare professionals. Many studies have revealed that medical schools, internationally, don’t pay a lot of attention to nutrition in the curriculum.

"The public – and even many health care professionals – may rightfully be confused about heart-healthy eating, and they may feel that they don't have the time or the training to evaluate the different diets," Gardner said. "We hope this statement serves as a tool for clinicians and the public to understand which diets promote good cardiometabolic health."

Cardiometabolic health refers to the processes that affect metabolism and the risk of heart and vascular disease. It encompasses blood glucose, cholesterol and other fats, blood pressure and weight. If several of these markers are of concern, the risk of heart disease increases.

While there’s no shortage of information on paleo, keto, low-carb, low-fat and Mediterranean eating lifestyles, this latest study is the first of its kind to measure them against heart health factors, and aims to weed out conflicting advice.

The AHA also acknowledges the need for these guidelines to also take into consideration cultural differences, food security and food deserts that restrict access to healthy food, and to be inclusive of historically marginalized groups.

"If implemented as intended, the top-tier dietary patterns align best with the American Heart Association's guidance and may be adapted to respect cultural practices, food preferences and budgets to enable people to always eat this way, for the long term," Gardner said.

The research was published in the journal Circulation.