— -- Every year Americans adopt new diet trends, from the juicing craze to gluten-free diets, and each new fad promises health benefits such as weight loss and higher energy.
But, as specific diets become more popular, doctors wanted to assess whether they would help the one part of the body that carries the most risk for both men and women in the U.S.: the heart.
In order to get a better sense of which diets were the most heart healthy, researchers examined more than 25 peer-reviewed studies and published their findings today in a new report in the Journal of the American College of Cardiology.
"There is sort of mass confusion about what foods are healthy or not healthy," lead study author Dr. Andrew Freeman, Director of Cardiovascular Prevention and Wellness at National Jewish Health in Denver, Colorado, told ABC News.
"When you take the time to weigh through the data and the evidence it becomes clear," he continued. "Human beings haven’t changed all that much in the last many, many years."
Researchers from 12 institutions, including George Washington University School of Medicine and National Jewish Health, analyzed the studies —- which together included tens of thousands of participants –- in order to determine what types of foods appear, given currently available research, to help the heart.
After an in-depth review of the scientific data, researchers found the most heart-healthy diet includes foods like extra-virgin olive oil, antioxidant-rich berries, green leafy vegetables, plant-based proteins, nuts in moderation and can include lean meats. To cut down on cholesterol, the study authors suggest limiting or eliminating coconut and palm oils, which are high in saturated fatty acids, and eggs, which raise the level of cholesterol in the bloodstream.
"Dietary requirements haven’t really changed," Freeman continued. "The diet that is most cardioprotective is mostly plant based ... predominantly fruits, vegetables, whole grains, and limited amounts of animal products if any."
However, Dr. Keith Ayoob, Associate Professor of Pediatrics at Albert Einstein College of Medicine, who was not involved in the studies, says that diet issues are rarely so black and white and that doctors need to approach each patient’s diet in a more holistic manner.
"When you’re talking about dietary cholesterol, sometimes I get more concerned with the companion foods. What kind of company are those eggs keeping?" Ayoob said. "Do you eat them plain boiled, fried in butter, cooked with olive oil?"
Simply relying on advice like eating in moderation is too vague, Ayoob added, and can mean different things for different people. He said patients should be given more guidance about exactly how to eat healthy.
"I think the idea of moderation is more of a mantra," Ayoob said. "But I think we would do well to define it a little bit better."
In addition to looking at the benefits of specific foods, researchers looked for evidence that recent popular diets to limit gluten or consume vegetables and fruits via juicing were heart healthy. Researchers found that the process of juicing fruits and vegetables with pulp removal actually concentrates the sugars more, making it easier to ingest more calories than needed. Adding sweeteners such as sugar or honey also increase caloric content of juices. The researchers found that the data regarding juicing where the pulp is retained is inconclusive for determining whether it provides harm or benefit for heart health.
"There are things that you’re going to have in the whole fruit that you can’t get into the juice," said Ayoob. "Also the other side is to remember that your gut is a great juicer, it just works more slowly. Let your teeth and digestive tract do what it’s supposed to do. And the fiber in fruits and vegetables is critical to a healthy diet."
Another trendy diet that was evaluated is a gluten-free diet, which has been proven to be a good treatment for patients who have gluten-related disorders such as celiac disease, wheat allergy, and nonceliac gluten sensitivity.
But only about 1 in 141 Americans have celiac disease, according to the National Institutes of Health. However, according to a Gallup poll in 2015, one in five Americans actively tries to avoid gluten in their diets. Researchers say there is no evidence that a gluten-free diet helps with weight loss in healthy individuals and some studies even show weight gain on a gluten-free diet. Gaining weight to the point of obesity is significantly associated with increased risk of heart disease.
"Our message here is if you are gluten sensitive, allergic, or have celiac disease, you should avoid gluten," says Freeman. "Otherwise gluten is not necessarily the enemy."
The studies reviewed in the analysis published today have a few limitations: Some of the foods and trends have not been studied over as long a time as others, there can be a "complex interplay" between nutrients in individuals and the lifestyle habits of the people included may have had some effect on their heart health.
For those searching for a heart-healthy diet, Freeman has some simple advice.
"If people want to eat animal products they should limit it as much as they’re willing, especially if they have risk factors for heart disease," he said. "For my patients I try to get them to go as low as they’re willing."
Ayoob agrees with increasing fruit and vegetable intake in the general population, but cautions against telling people to strictly eliminate certain foods from their diets. "Because a diet, no matter how nutritious," he says, "is only nutritious if people stay on it."
Dr. Joyce Park is a New York-based dermatologist at NYU Langone Medical Center and resident in the ABC News Medical Unit.