A new American Heart Association (AHA) scientific statement – the first of its kind – rates how closely several popular diets align with its guidance for heart-healthy eating.
Perhaps unsurprisingly, the DASH diet came out on top, with a score of 100, closely followed by pescatarian and Mediterranean diets. However, some regimes – in particular, very low-carb/ketogenic diets, which received the lowest score, at 31 – contradict the AHA’s dietary guidance and are deemed unsustainable, according to a scientific statement published in the journal Circulation in April.
“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 Christopher D Gardner, Rehnborg Farquhar Professor of Medicine at Stanford University, California, who chaired the writing committee for the statement.
“The public — and even many healthcare 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. We hope this statement serves as a tool for clinicians and the public to understand which diets promote good cardiometabolic health.”
Ten categories of dietary pattern identified
The statement rates how well popular diets align with the AHA’s Dietary Guidance, which includes 10 key features of a dietary pattern to improve cardiometabolic health.
Dietary patterns were grouped by similarity in key characteristics, resulting in 10 categories: DASH-style; Mediterranean-style; vegetarian-style/pescatarian; vegetarian-style/ovo/lacto; vegetarian-style/vegan; low-fat; very low-fat; low-carbohydrate; paleolithic; and very low-carbohydrate/ketogenic.
Defining features of the diets were given points based on how well each feature aligned with the AHA guidance – one point for fully meeting the guidance, 0.75 points for mostly meeting it, and 0.5 points for partially meeting it. The resulting total was adjusted to create a rating from 0-100, with 100 indicating the closest adherence to the guidance.
Top tier: DASH-style diet comes out on top
The four patterns with the highest ratings (85 and above) are low in salt, added sugar, alcohol, tropical oils, and processed foods, and rich in non-starchy vegetables, fruits, whole grains, and legumes. Protein tends to come from plant sources; fish or seafood, lean poultry, and meats; and low-fat or fat-free dairy products.
The DASH-style eating pattern came top with 100, followed by pescatarian diets at 92, and the Mediterranean-style diet at 89. The latter received a lower rating as it fails to explicitly address added salt and allows moderate alcohol consumption. Ovo/lacto diets came in fourth place, at 86.
Tier 2: Vegan and low-fat diets (scores 75-85)
Both second-tier diets – vegan and low-fat – received a score of 78. While both also emphasise eating vegetables, fruits, whole grains, legumes, and nuts, restrictions in the vegan diet can create problems for adherence. Moreover, veganism may increase the risk of vitamin B12 deficiency, which can lead to anaemia.
Low-fat diets often treat all fats equally, while the AHA guidance suggests replacing saturated fat with healthier fats such as mono- and polyunsaturated fats. People who follow a low-fat diet may over-consume less healthy sources of carbohydrates, such as added sugars and refined grains.
Tier 3: Very low-fat and low-carb diets (scores 55-74)
Very low-fat diets scored 72; points were lost for restricting nuts and healthy (non-tropical) plant oils, and these diets may also result in deficiencies of vitamin B12, essential fatty acids, and protein.
Low-carb diets received a rating of 64. When restricting carbohydrates, followers tend to decrease consumption of fibre while increasing consumption of saturated fat, both of which contradict the AHA guidance.
The statement suggests that loosening restrictions on food groups such as fruits, whole grains, legumes, and seeds may help people stick to a lower-carbohydrate eating pattern while promoting heart health over the long term.
Tier 4: Paleolithic and very low-carb/ketogenic diets (scores less than 55)
The lowest-rated eating patterns, often used for weight loss, align poorly with the dietary guidance. Strengths of very low-carb eating patterns – which received a score of 31 – include the emphasis on consuming non-starchy vegetables, nuts, and fish, along with minimising consumption of alcohol and added sugar.
However, restrictions on fruits, whole grains, and legumes may result in reduced fibre intake, while these diets are high in fat without limiting saturated fat. Consuming high levels of saturated fat and low levels of fibre are both linked to the development of cardiovascular disease.
“There really isn’t any way to follow the Tier 4 diets as intended and still be aligned with the American Heart Association’s Dietary Guidance,” Gardner said. “They are highly restrictive and difficult for most people to stick with long term.
“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.”
