"By incorporating a single food that is easy to consume, easy to carry, doesn't need to be cooked -- just by changing one food in an already healthy diet -- you can accomplish a great health benefit," Joan Sabaté, MD, tells WebMD. A study authored by Sabaté and his colleagues appears in this month's Annals of Internal Medicine.
"All heart-healthy diets lower total and LDL cholesterol; however, during the walnut diet we observed a 5% and 6% reduction, respectively, beyond the effects of the Mediterranean diet alone," says Sabaté. "It's significant from a statistical standpoint, but relevant from a practical point." Walnut oil could have similar effects to whole walnuts, but that has not yet been investigated.
This study expands on Sabaté's previous research to include women, people with high cholesterol, and middle-aged and older people. Also, other studies have been conducted with meals prepared in a laboratory setting, while this study involved "free-living persons" who were advised to eat a Mediterranean diet, says Sabaté, professor and chair of nutrition at Loma Linda University's School of Public Health in Loma Linda, California.
In his study, conducted in Barcelona, Spain, the 49 men and women all had high total cholesterol and high LDL ("bad") cholesterol. People with a family history of high cholesterol levels -- whether genetic or not -- were not included in the study.
All were asked to eat a Mediterranean diet composed of fresh fruits and vegetables, fish (no red meat or eggs), and olive oil for cooking. Those on the "walnut diet" substituted eight to 11 walnuts a day for part of the olive oil/fat portion of the diet. Patients followed each diet for six weeks, since it takes four weeks for cholesterol levels to stabilize after diet changes.
The overall cholesterol level decreased by 9% during the walnut diet but only by 5% when eating the no-walnut diet. Similarly, the LDL, "bad," cholesterol levels decreased by about 11% during the walnut diet and almost 6% during the no-walnut diet. Cholesterol ratios also improved with walnuts.
"Except for almonds, no other nut has been as well studied as walnuts," Sabaté tells WebMD. "In a couple of studies, almonds have been shown to lower total cholesterol and LDL levels without changing ["good" cholesterol]. They showed very similar results to our study. It's a reasonable assumption that any nuts from the same group could have that effect, but as a scientist, I cannot say so. Research has to be done to prove this."
His study also helps quiet a controversy in nut research. "It has been suspected that nuts, because they are high in polyunsaturated fat, could actually increase LDL ["bad" cholesterol] levels. However, we did not observe [this] in the walnut diet," says Sabaté.
In fact, he adds, "by incorporating a few walnuts a day into a typical Western diet, we can expect even greater benefits -- if saturated fat is replaced by walnuts."
Besides, adds Sabaté, walnut patties and meatballs are crunchier, with richer texture and flavor than their beef-based counterparts. "My wife makes walnut balls and almond balls instead of meatballs and, to me, they are far more tasty than meatballs."
In reviewing the study, Ronald Krauss, MD, member and past chairman of the American Heart Association's nutrition committee, tells WebMD, "Can people gobble a bunch of walnuts and get similar results? I don't think we can say that."
Krauss brings up another issue. "Obesity is entering the picture more and more as a major contributor not only to heart disease but also diabetes. Nuts are rich in fat and high in calories, so we always have to temper our enthusiasm. If you eat too many nuts, you get too many calories. And that's always a caution."
- A recent study shows that a Mediterranean diet that includes a handful of walnuts each day can lower "bad" cholesterol even more than the same diet without the nuts.
- Researchers believe that walnut oil could have positive effects on cholesterol, but it has not been studied.
- Also, in other studies, almonds have been found to have some benefit.
- One expert cautions that walnuts are rich in fat and calories.