April 24, 2000 -- Add the macadamia to the growing list of healthy nuts. A study from the University of Hawaii shows that a diet containing the high-fat nuts can actually improve cholesterol levels.
"The conventional wisdom still is that macadamia nuts are so good that they must be bad for you," says Curb. "This study indicates that its preconception is not true and that macadamia nuts can actually be part of a healthy diet," lead researcher J. David Curb, tells WebMD. Curb is a professor of geriatric medicine and clinical epidemiology at the University of Hawaii School of Medicine and chief of the Division of Clinical Epidemiology in Honolulu. Similar benefits have also been reported with walnuts, almonds, and pecans.
"Macadamia nuts have a bad reputation for having a lot of fat, but our research shows the fats they contain, especially monounsaturated fatty acids, don't adversely impact cholesterol," he says.
One ounce of macadamia nuts contains 20.9 grams of fat per once, and 88% of the calories come from fat, according to the U.S. Department of Agriculture. By comparison, pecans contain 19.2 grams of fat, almonds contain 14.8, walnuts contain 17.6, and peanuts contain 13.8 grams of fat per ounce.
Researchers in the new study, which appears in the April 24 issue of the journal Archives of Internal Medicine, compared three diets. One diet, classified as a "typical American" diet, contained 37 percent of calories from fat. The second diet was similar but with the fat calories derived from macadamia nuts. The third was the American Heart Association's "prudent diet," with 30% of the calories from fat. In the study, 15 men and 15 women, 18-59 years old, ate each of the three diets for four weeks. Calories were adjusted to maintain constant weight levels, and menus contained common local foods. All meals were prepared and eaten in the college cafeteria.
Blood fat analysis showed cholesterol levels after the macadamia nut diet were similar to the low-fat diet and lower than the typical American diet. The macadamia nut diet produced lower levels of triglycerides, an important form of blood fat, than either of the other diets. Despite an increase in the proportion of fat in their diets, volunteers showed no significant change in weight or cholesterol levels.
Researchers saw no negative side effects from eating the macadamia nuts, and, according to Curb, these results were similar to findings from an earlier study he conducted in which volunteers ate a diet containing large quantities of ground macadamia nuts for one month.
Curb says macadamia nuts are high in oleic acid, a monounsaturated fatty acid also found in olive oil and canola oil, which is believed to be beneficial in cutting cholesterol. Also, the nuts are the only food to also contain significant amounts of palmitoleic acid, another monounsaturated fatty acid.
A report in the September 1999 issue of the journal Circulation says some studies have found that monounsaturated fats may make platelets -- clotting components in the blood -- less sticky and less likely to form clots in blood vessels, helping to prevent a heart attack or stroke.
The macadamia study is just the latest research on the benefits of eating tree nuts. In 1999, French researchers reported that people in the Dauphine region of France who frequently consumed walnuts or walnut oil -- typically used in salad dressings -- had higher levels of HDL-cholesterol and apo A1 -- a beneficial compound that circulates with blood fat -- than did people who never ate walnuts.
Also, the American Heart Association (AHA) reports that in a 12-year study of more than 22,000 doctors in the Physicians Health Study, men whose diets contained high quantities of nuts had a decreased risk of dying from heart disease. And last February, researchers at New Mexico State University announced eating pecans lowered low-density lipoprotein (LDL) -- the "bad" cholesterol -- linked to heart disease.
The American Dietetic Association agrees that nuts are very nutritious. The ADA points out that all are rich in protein, potassium, zinc, vitamin E, magnesium, carbohydrates, and folic acid. The ADA suggests mixing the nuts with other foods to harness the nutrition and flavor of nuts.
Curb says longer studies and studies using differing proportions of other nutrients, such as protein and carbohydrates, are needed to better characterize the potential benefits of a macadamia-based diet high in monounsaturated fat. "After that, high monounsaturated fat diets appropriate for long-term consumption in populations need to be developed and tested," he says.
Funding for the study came from the U.S. Army Medical Research Acquisition Activity in Frederick, Md.
- A new study shows that people who consume a diet containing high-fat macadamia nuts have the same cholesterol levels as those on a low-fat diet.
- Monounsaturated fats in nuts may produce several health benefits, including improved blood fat profiles and reduced risk of heart disease.
- The American Dietetic Association agrees that nuts can be very nutritious but advises people to choose portions that keep the amount of fat low.