Fatty acids are long-chained molecules having an alkyl group at one end and a carboxylic acid group at the other end. Fatty acid viscosity (thickness) and melting temperature increases with decreasing number of double bonds. Therefore, monounsaturated fatty acids have a higher melting point than polyunsaturated fatty acids (more double bonds) and a lower melting point than saturated fatty acids (no double bonds). Monounsaturated fatty acids are liquids at room temperature and semisolid or solid when refrigerated.
 Molecular description of oleic acids
Common monounsaturated fatty acids are palmitoleic acid (16:1 n−7), cis-vaccenic acid (18:1 n−7) and oleic acid (18:1 n−9). Palmitoleic acid has 16 carbon atoms with the first double bond occurring 7 carbon atoms away from the methyl group (and 9 carbons from the carboxyl end). It can be lengthened to the 18-carbon cis-vaccenic acid. Oleic acid has 18 carbon atoms with the first double bond occurring 9 carbon atoms away from the carboxylic acid group. The illustrations below show a molecule of oleic acid in Lewis formula and as a space-filling model.
 Relation to health
Although polyunsaturated fats protect against cardiovascular disease by providing more membrane fluidity than monounsaturated fats, they are more vulnerable to lipid peroxidation (rancidity). On the other hand, some monounsaturated fatty acids (in the same way as saturated fats) may promote insulin resistance, whereas polyunsaturated fatty acids may be protective against insulin resistance. Furthermore, the large scale KANWU study found that increasing monounsaturated fat and decreasing saturated fat intake could improve insulin sensitivity, but only when the overall fat intake of the diet was low.
Foods containing monounsaturated fats reduce low-density lipoprotein (LDL) cholesterol, while possibly increasing high-density lipoprotein (HDL) cholesterol. However, their true ability to raise HDL is still in debate.
Levels of oleic and monounsaturated fatty acids in red blood cell membranes were positively associated with breast cancer risk. The saturation index (SI) of the same membranes was inversely associated with breast cancer risk. Monounsaturated fats and low SI in erythrocyte membranes are predictors of postmenopausal breast cancer. Both of these variables depend on the activity of the enzyme 9-d delta 9 desaturase.
In children, consumption of monounsaturated oils is associated with healthier serum lipid profiles.
It is recommended that 10-15% of an adult’s daily calorie intake comes from Monounsaturated fats.
 Natural sources
Monounsaturated fats are found in natural foods such as red meat, whole milk products, nuts and high fat fruits such as olives and avocados. Olive oil is about 75% monounsaturated fat. The high oleic variety sunflower oil contains as much as 85% monounsaturated fat. Canola oil and Cashews are both about 58% monounsaturated fat. Tallow (beef fat) is about 50% monounsaturated fat and lard is about 40% monounsaturated fat. Other sources include macadamia nut oil, grapeseed oil, groundnut oil (peanut oil), sesame oil, corn oil, popcorn, whole grain wheat, cereal, oatmeal, safflower oil, almond oil, sunflower oil, tea-oil Camellia, and avocado oil.
This article uses material from the Wikipedia article Monounsaturated Fat, which is released under the Creative Commons Attribution-Share-Alike License 3.0.