Nutrition and Nutritional Biochemistry: Lipids

Nutritional Aspect of Lipids

• Lipids are present in the human diet and account for 10 to 20% of the body weight, with 90% of lipids stored in adipose tissues.
• Lipids in the human diet come from animal and plant origins, consisting mainly of triacylglycerol, with some dissolved cholesterol and fat-soluble vitamins.

Medium Chain Triacylglycerol

• Medium chain triacylglycerol has a caloric value of 9 Cal/g, compared to 4 Cal/g for carbohydrates.
• Medium chain triacylglycerol is used as an alternative source of fat energy, especially in cases where individuals are unable to digest or metabolize long-chain triacylglycerol.
• Medium chain triacylglycerol is digested in the stomach, absorbed, and transported directly to the liver, where it is rapidly metabolized by beta-oxidation.
• Medium chain triacylglycerol is found in coconut oil and palm kernel oil.

Fatty Acids Classifications

• Fatty acids can be classified into three categories: saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA).

Saturated Fatty Acids (SFA)

• Major SFA in the diet include C14, C16, and C18, except in milk and coconut oil, where SFA range from C4 to C18.

Monounsaturated Fatty Acids (MUFA)

• Major MUFA in the diet is oleic acid (C18:1n-9).

Polyunsaturated Fatty Acids (PUFA)

• Major PUFA in the diet include linoleic acid (C18:2n-6) and alpha-linolenic acid (C18:3n-3).

Omega-3 Fatty Acids Family

• Omega-3 fatty acids include alpha-linolenic acid (ALA, 18:3 n-3), eicosapentaenoic acid (EPA, 20:5 n-3), and docosahexaenoic acid (DHA, 22:6 n-3).
• Omega-3 fatty acids have three, five, or six double bonds, respectively.
• Omega-3 fatty acids are essential and cannot be synthesized by the human body.

Omega-6 Fatty Acids Family

• Omega-6 fatty acids include linoleic acid (LA, 18:2 n-6) and arachidonic acid (AA, 20:4 n-6).
• Omega-6 fatty acids have two or four double bonds, respectively.
• Omega-6 fatty acids are essential and cannot be synthesized by the human body.

Omega-9 Fatty Acids Family

• Omega-9 fatty acids include oleic acid (18:1n-9), which has one double bond.
• Main sources of oleic acid are olive, canola, avocado, and oilseeds.

Ratio of Omega-6 to Omega-3 Fatty Acids

• The ideal ratio of omega-6 to omega-3 fatty acids in the diet is approximately 1:1.
• A higher ratio of omega-6 to omega-3 fatty acids has been linked to various diseases, including cardiovascular disease, cancer, osteoporosis, and inflammatory and autoimmune diseases.

Trans Fatty Acids (TFA)

• Main sources of trans fatty acids are partially hydrogenated fats and fried foods.
• A small proportion of trans fatty acids also comes from ruminant animals (fat and whole milk).

Effect of Dietary Lipid on Lipid Metabolic Pathways

• Omega-3 fatty acids EPA and DHA decrease triglyceride hepatic synthesis and increase beta-oxidation in the liver.

Benefits of Omega-3 Fatty Acids

• Omega-3 fatty acids can reduce chronic inflammation by enzymatic competition for eicosanoids synthesis, reducing expression of cell adhesion molecules, and suppressing production of cytokines such as interleukin 6.
• Omega-3 fatty acids can improve risk factors for cardiovascular diseases and heart stroke by:
  • Reducing blood pressure
  • Reducing triglycerides
  • Raising HDL cholesterol levels
  • Promoting release of nitric oxide from endothelial cells.