Avocados are high in fiber and rich in healthy monounsaturated fats. They also contain a wide variety of vitamins, minerals and micronutrients, among them the antioxidant vitamins C and E; vitamin K, which appears to preserve bone health in older people; potassium, which may help regulate blood pressure; lutein, which appears to protect eye health; and folate, an important B vitamin.

Most of the nutrients are present in small amounts, however, and while studies have suggested numerous health benefits, few Americans eat avocados on a regular basis, so "it’s hard to study avocado comprehensively,” the way many other foods are studied, said Penny M. Kris-Etherton, a professor of nutrition at Pennsylvania State University.

Several clinical trials have reported that diets that incorporate avocado may help lower levels of L.D.L., or "bad,” cholesterol, because the fruit contains plant sterols called phytosterols that compete with cholesterol for absorption in the intestines. One small clinical trial found that women with Type 2 diabetes who followed a diet rich in monounsaturated fats, including those from avocados, had lower triglyceride levels. Another small trial suggested avocados may improve vascular health and have anti-inflammatory effects. Some papers have reported that an extract made of avocado and soybean oils may alleviate pain from osteoarthritis, but a 2003 systematic review concluded that the data were mixed.

A 2013 study, funded by the Hass Avocado Board, found that overweight subjects who ate about half an avocado a day felt more sated compared with subjects on an avocado-free diet.

But one drawback to avocados is their high calorie count, about 250 calories per fruit, Dr. Kris-Etherton said. "So people have to be careful – they can’t just add an avocado a day to a bad diet and see health benefits.”