Monounsaturated fat

For discussion how dietary fats affect cardiovascular health, see Diet and heart disease.

In biochemistry and nutrition, monounsaturated fats are fatty acids that have a single double bond in the fatty acid chain and all the carbon atoms in the chain are single-bonded. By contrast, polyunsaturated fatty acids have more than one double bond.

Fatty acids are long-chained molecules having a methyl group at one end and a carboxylic acid group at the other end. Fatty acid fluidity increases with increasing number of double bonds. Therefore, monounsaturated fatty acids have a higher melting temperature than polyunsaturated fatty acids but lower than saturated fatty acids. Monounsaturated fatty acids are liquids at room temperature and semisolid or solid when refrigerated.

Molecular description: oleic acid

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 bum 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 methyl 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 (like saturated fats) promote insulin resistance, whereas polyunsaturated fatty acids are protective against insulin resistance . In direct contrast to this, the large scale KANWU study found that neither dietary monounsaturated or supplemented polyunsaturated fats (in the form of fish oil) affected insulin sensitivity, while increased consumption of saturated fat induced a significant decrease in this parameter.

Foods containing monounsaturated fats lower LDL cholesterol, while possibly raising HDL cholesterol. However, their true ability to raise HDL is still in debate.

Olive oil is a key component of Mediterranean cuisine, widely regarded as being protective against cardiovascular disease, while tea oil is a traditional part of Asian cuisine.

In a study published in 2001, erythrocyte membrane oleic and monounsaturated fatty acid content was positively associated with breast cancer risk in postmenopausal women, while no association was shown between saturated fatty acids and breast cancer risk. Enzyme Δ9-desaturase catalyzes the conversion of stearic acid to oleic acid: there is a negative correlation between erythrocyte membrane oleic acid and dietary polyunsaturated fatty acids. Inverse relationship between Saturation Index (ratio of membrane stearic to oleic acid) and breast cancer risk could also be related to hormonal and metabolic factors and to interactions between them, as well as to dietary factors.

In children, consumption of monounsaturated oils is associated with healthier serum lipid profiles.

Natural sources

Monounsaturated fats are found in natural foods such as nuts and avocados, and are the main component of tea seed oil and olive oil (oleic acid). Canola oil is 57%–60% monounsaturated fat, olive oil is about 75% monounsaturated fat while tea seed oil is commonly over 80% monounsaturated fat. Other sources include grapeseed oil, ground nut oil, peanut oil, flaxseed oil, sesame oil, corn oil, popcorn, whole grain wheat, cereal, oatmeal, safflower oil, sunflower oil, tea-oil Camellia.

See also

• High density lipoprotein
• Saturated fat
• Unsaturated fat
  • Polyunsaturated fat

External links

• Fats (Mayo Clinic)
• Types of Fats (Cardiovascular Consultants) Some "dated" information.
• The Chemistry of Unsaturated Fats