With so many diet fads around these days, how do you know which ones are actually good for you?

In a new review of studies covering about 40 years, researchers attempted to dispel the hype surrounding some popular diet trends and to outline what experts really know about a heart-healthy diet. They presented what might be considered the "best" dietary pattern for reducing the risk of heart disease, and explained why consumers should be wary of nutrition fads such as antioxidant pills and juicing.

The bottom line: A heart-healthy diet is one that's high in fruits, vegetables, whole grains and legumes, and includes nuts in moderation. Heart-healthy diets may also include limited amounts of lean meat, fish, low-fat and nonfat dairy products, and liquid vegetable oils, the researchers said. In contrast, people should avoid saturated, trans and solid fats; sodium; added sugars; and refined grains.

"There is a growing consensus that a predominantly plant-based diet that emphasizes green, leafy vegetables; whole grains; legumes; and fruit is where the best improvements are seen in heart health," study co-author Dr. Andrew Freeman, a cardiologist and director of cardiovascular prevention and wellness at National Jewish Health hospital in Denver, said in a statement. On the other hand, "there is a great amount of misinformation about nutrition fads, including antioxidant pills, juicing and gluten-free diets," Freeman said.

The review of studies had the following conclusions about these popular diet trends:

Juicing: There are few studies that have compared the benefits of juicing your fruits and vegetables with the benefits of consuming them whole, according to the review. In addition, "the process of juicing concentrates calories," which makes it much easier to ingest too many, the researchers said. Until more studies are available, the researchers recommend consuming whole fruits and vegetables. Juicing should be reserved for situations in which people aren't getting enough fruits and vegetables in their daily diet, they said. If people do juice, they should be careful not to consume too many calories from the juice, and they should avoid adding additional sugars, such as honey, the researchers recommended. 

Antioxidant supplements: Rigorous studies have not found any benefits on heart health from taking high-dose antioxidant supplements. The current evidence shows fruits and vegetables are the healthiest and most beneficial source of antioxidants, the researchers said.

Gluten-free diets: People with celiac disease, gluten sensitivity or a wheat allergy should avoid gluten. But there's no evidence that avoiding gluten will help people without these conditions lose weight or have any benefit on heart health, the researchers said.

Coconut and palm oils: Coconut oil and palm oil are high in saturated fatty acids, which are fats that are known to raise people's blood cholesterol levels, according to the American Heart Association. There's little evidence that these oils are beneficial for heart health, and some studies even suggest that palm oil may increase heart disease risk, the researchers said. For these reasons, the use of coconut oil and palm oil should be discouraged, the researchers concluded. In contrast, liquid vegetable oils, such as olive oil, are linked with heart-health benefits, such as lower levels of "bad cholesterol" and higher levels of "good cholesterol," the researchers said. Still, these oils are high in calories and should be used in moderation.

Nuts: Nuts can be part of a heart-healthy diet, but people should be careful not to consume too many nuts, because they are high in fats and calories, the researchers said.

The researchers noted that there are challenges in studying the role of nutrition in the prevention of diseases, and these challenges may lead to conflicting findings, thus resulting in confusion of which diets are healthy.

For example, people who have healthy diets often also engage in other healthy behaviors, such as getting regular exercise and avoiding smoking, and it can be hard to separate the effects of these behaviors from those of a diet, Freeman said.

In addition, some studies rely on people's memories of what they ate on a certain day, and these memories aren't always reliable, he said. New technologies, such as smartphones, may allow people to do a better job of recording what they ate, and lead to more robust evidence for nutrition research, the researchers said.

The review is published today (Feb. 27) in the Journal of the American College of Cardiology.