Incorporating more nut and nut-containing foods into the diet at the expense of foods full of saturated fats could reduce cholesterol levels by six per cent, suggests a new study with macadamia nuts.
The ratio of total cholesterol to HDL cholesterol, reported to be the most specific lipid risk factor for cardiovascular disease (CVD), decreased by 0.29 after consuming a macadamia-rich diet for five weeks, according to the randomised, crossover, controlled feeding study with 25 healthy participants.
The study, published in this month's issue of the Journal of Nutrition, adds to an ever-growing body of science, particularly epidemiological studies, linking nut consumption to improvements in markers of cardiovascular health. Previously, researchers have reported benefits for both almonds and walnuts.
Researchers from Pennsylvania State University and the University of Guelph compared blood cholesterol levels after consuming a typical American diet or a macadamia nut-rich diet. They note that the nuts are a rich source of both polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA)
Lead author of the study Amy Griel reports that the 15 women and 10 men were randomly assigned to five weeks of consuming either an average American diet (AAD) consisting of 33 per cent total fat, 13 per cent saturated fatty acids (SFA), 11 per cent MUFA, and five per cent PUFA, or the macadamia nut-rich diet (42.5 grams of nuts), providing 33 per cent total fat, seven per cent SFA, 18 per cent MUFA, and five per cent PUFA.
The subjects were all classed as mildly hypercholesterolemic. High cholesterol levels, hypercholesterolaemia, have a long association with many diseases, particularly CVD.
Griel and co-workers report that total cholesterol and LDL cholesterol levels decreased after consuming the macadamia nut-rich diet. Indeed, levels were 4.94 and 3.14 mmol/L, respectively, compared to 5.45 and 3.44 mmol/L after consuming the average American diet.
Furthermore, the ratio of total cholesterol to HDL cholesterol and LDL to HDL decreased after five weeks of eating the nut-rich diet. The former ratio was 4.60, compared to 4.89 following the average American diet, while the latter ratio was 2.91 after the nut-rich diet, compared to 3.09 following the average American diet.
"Thus, macadamia nuts can be included in a heart-healthy dietary pattern that reduces lipid/lipoprotein CVD risk factors," wrote Griel.
"Nuts as an isocaloric substitute for high SFA foods increase the proportion of unsaturated fatty acids and decrease SFA, thereby lowering CVD risk," she added.
An alternative to statins?
The new research could be significant in reducing the incidence of high cholesterol as health care professionals are increasingly recommending a dietary approach to controlling cholesterol over prescription drugs such as statins, which may have serious side effects.
CVD causes almost 50 per cent of deaths in Europe, and is reported to cost the EU economy an estimated €169bn ($202bn) per year. According to the American Heart Association, 34.2 per cent of Americans (70.1m people) suffered from some form of cardiovascular disease (CVD) in 2002.
Beyond lowering cholesterol, PUFA-MUFA balance has also been linked with prevention of Parkinson's disease. In 2005 a Dutch study published in Neurology (2005; Vol. 64, pp. 2040-2045) indicated that higher consumption of both types of unsaturated fat may help stave off the degenerative disease.
Source: Journal of Nutrition
2008, Volume 138, Pages 761-767
"A Macadamia Nut-Rich Diet Reduces Total and LDL-Cholesterol in Mildly Hypercholesterolemic Men and Women"
Authors: A.E. Griel, Y. Cao, D.D. Bagshaw, A.M. Cifelli, B.Holub, P.M. Kris-Etherton