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Q: I am trying to eat more nuts as part of my effort to eat healthier. Is one kind of nut healthier than others?

A: Many studies have found that people with higher nut consumption have improved cardiovascular risk factors and lower rates of cardiovascular disease. For example, several trials have linked nut consumption with lower blood pressure and cholesterol levels.

And nuts are an important part of the Mediterranean style diet, which has been found to be heart-healthy as well.

A new study suggests that walnuts may be a particularly good choice. And this isn’t the first time researchers have come to this conclusion.

A previous analysis by the same researchers (including 365 study participants in 13 trials) found that diets enriched with walnuts led to lower total and LDL (“bad”) cholesterol when compared with other diets. Since then, more studies with far more study participants and longer follow-up have been published.

This latest analysis combined data from 26 previous trials that included more than 1,000 people; compared with those on a regular diet, those consuming a walnut-enriched diet had:
— lower total cholesterol (by about 7 mg/dL, representing a 3 percent greater reduction),
— lower LDL cholesterol (by about 5.5 mg/dL, a 4 percent greater reduction),
— lower triglycerides (by about 5.7 mg/dL, a 5.5 percent greater reduction), and
— lower apolipoprotein B (a protein linked to cardiovascular disease) by nearly 4 mg/dL.

While these improvements in blood lipids were rather small, larger improvements (for example, a 12 mg/dL drop in total cholesterol) were noted when the comparison diet was a typical U.S. or Western diet (that is, a diet high in red meats, high-fat dairy foods, and artificially sweetened foods).

A diet rich in high-fat foods such as nuts always raises the concern about the potential for weight gain, but fortunately those on the high-walnut diet did not gain weight.

While this new research is intriguing, it also raises the question of whether walnuts are unique in some way. In fact, it may be the types of oils in walnuts that make them special when it comes to cardiovascular health.

Walnuts contain a lot of polyunsaturated fatty acids, which are healthier than saturated fats. In addition, walnuts have alpha-linolenic and linoleic acids, which may have anti-inflammatory effects that keep blood vessels healthy, in addition to having favorable effects on blood lipids.

All nuts are not created equal. Many nuts (such as my favorites, almonds and cashews) are rich in monounsaturated fats, along with polyunsaturated fats. These are healthier types of fats than saturated and trans fats, but the specific combination of fats and polyunsaturated fatty acids contained in walnuts may be particularly good for cardiovascular health.

Robert H. Shmerling, M.D., is associate professor of Medicine at Harvard Medical School and Clinical Chief of Rheumatology at Beth Israel Deaconess Medical Center in Boston. For additional consumer health information, please visit www.health.harvard.edu.

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