"We looked at macadamia nuts because they are not currently included in the health claim for tree nuts, while other tree nuts are recommended as part of a healthy diet," says Dr. Amy E. Griel, recent Ph.D. recipient in nutritional sciences. "Macadamia nuts have higher levels of monounsaturated fats, like those found in olive oil compared with other tree nuts."
The researchers used a controlled feeding study to compare a heart-healthy diet with 1.5 ounces ?a small handful ?of macadamia nuts to a standard American diet. The participants had slightly elevated cholesterol levels, normal blood pressure and were not taking lipid lowering drugs. Researchers randomly assigned participants to either the macadamia nut diet or the standard American diet and provided all meals for the participants for five weeks. The participants then switched diets and continued eating only food provided by the researchers for another five weeks.
The Healthy Heart diet with macadamia nuts did reduce total cholesterol, low-density lipoprotein cholesterol and triglyceride levels compared with the standard American diet.
"We observed a reduction in LDL similar to that seen with other tree nuts like walnuts and almonds," says Griel.
Individual calorie levels were used for each participant so that they did not gain or lose weight during the study. Both diets were matched for total fat, containing 33 percent calories from total fat. The Heart Healthy diet with macadamia nuts had 7 percent saturated fat, 18 percent monounsaturated fat and 5 percent polyunsaturated fat. The standard American diet had 13 percent saturated fat, 11 percent monounsaturated fat and 5 percent polyunsaturated fat.
The macadamia nut diet included macadamia nuts as a snack, mixed into meals, as a salad topping and in cookies and muffins.
"The total fat was the same in both diets," says Griel. "We substituted the macadamia nuts for other sources of fat and protein in the diet. For example, we could switch skim milk for 2 percent milk and add some macadamia nuts."
Macadamia nuts are native to Australia, but were imported to Hawaii and thrived. The first commercials crop of Hawaiian macadamia nuts was harvested in 1956.