Robert H. Shmerling, MD
Faculty Editor, Harvard Health Publishing
For many, choosing a healthy diet is all about sacrifice: foregoing the appetizers, cutting back on carbs or saturated fat, giving up dessert. But what if there was something you really liked that turned out to be good for you? No, I’m not talking about chocolate (although in small quantities, chocolate may not be so bad!).
This time it’s nuts in the news. Previous 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 diet, which has been found to be heart-healthy as well.
A new study looks at health benefits of walnuts
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% greater reduction)
lower LDL cholesterol (by about 5.5 mg/dL, a 4% greater reduction)
lower triglycerides (by about 5.7 mg/dL, a 5.5% greater reduction)
lower apoprotein 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 US 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.
Why would walnuts be so good for you?
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.
Not so fast, walnut lovers
Before you start loading up on walnuts, there are some important caveats to keep in mind:
The improvements in blood lipids noted in this study were small.
This study did not determine the ideal “dose” or duration of walnut consumption. In one of the best studies, a mix of about nine hazelnuts, 12 almonds, and six walnuts were consumed daily. That might be more than some people are willing to eat!
A study of this type cannot prove that walnuts were the reason a person’s cholesterol improved with a walnut-enriched diet. It’s possible that those who like walnuts also tend to exercise more, smoke less, or have more favorable genes than those who don’t eat walnuts.
No single food in your diet can make you healthy. It’s the big picture that matters most. A healthy diet, regular exercise, avoiding excess weight, and not smoking are good starting points. And even with a healthy lifestyle, some people require medications or other treatments to reduce their risk of cardiovascular and other diseases.