Updated March 16, 2015.
Written or reviewed by a board-certified physician. See About.com's Medical Review Board.
In monounsaturated fatty acids (MUFA), there is one (and only one) double bond in the fatty acid carbon chain. All the other carbon atoms in the chain are joined by single bonds.
MUFA have gotten a lot of attention in recent years, mainly because MUFA (in the form of olive oil) is a major component of the Mediterranean diet. In several studies, people consuming this kind of diet have had a reduced risk of heart disease.
Also, in people with type 2 diabetes, replacing dietary polyunsaturated fatty acids with MUFA improves insulin resistance and vascular function.
Further, MUFA reduces levels of LDL cholesterol and triglycerides, and appears to reduce the oxidation of LDL cholesterol. (Oxidized LDL cholesterol is thought to play a major role in atherosclerosis.)
Despite the fact that the MUFA have such a favorable profile, a recent meta analysis of observational studies found no good correlation between the consumption of MUFA and a reduced risk of coronary artery disease. For this reason US dietary guidelines do not strongly recommend eating a lot of MUFA, though they prefer them to saturated fat.
On the other hand, based on the benefits of the Mediterranean diet and the effect of MUFA on lipid profiles, the American Heart Association classifies MUFA as “good fat,” and favors substituting MUFA for saturated fat in the diet.
MUFA can be found in olive oil, peanut butter, avocado, and various nuts and seeds.
Sources:
Schwingshackl L, Hoffmann G. Monounsaturated fatty acids and risk of cardiovascular disease: synopsis of the evidence available from systematic reviews and meta-analyses. Nutrients 2012; 4:1989.
Ryan M, McInerney D, Owens D, et al. Diabetes and the Mediterranean diet: a beneficial effect of oleic acid on insulin sensitivity, adipocyte glucose transport and endothelium-dependent vasoreactivity. QJM 2000; 93:85.
Nordmann AJ, Suter-Zimmermann K, Bucher HC, et al. Meta-analysis comparing Mediterranean to low-fat diets for modification of cardiovascular risk factors. Am J Med 2011; 124:841.
Esposito K, Marfella R, Ciotola M, et al. Effect of a mediterranean-style diet on endothelial dysfunction and markers of vascular inflammation in the metabolic syndrome: a randomized trial. JAMA 2004; 292:1440.
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