diet

• Lipids


  Dietary fats
• Dietary lipids (dietary fats)

  • Provide energy (1 gram = 9 kcal)
  • Control body temperature
  • Protect body from external influences by surrounding organs with adipose tissue
  • Allow the absorption of fat-soluble vitamins in the body
  • 25-30% of our daily energy intake should come from dietary fats

  
• Lipid Terminology


  • Triglycerides
  • Phospholipids
  • Sterols
• Triglycerides


  The major class of dietary lipids, including fats & oils. Made up of 3 units of FAs and 1 unit of glycerol. Comprise about 95% of lipids in food and the human body
• Phospholipids


  2nd of three main classes of lipids, similar to a triglyceride, but contains Phosphorus
• Sterols


  3rd of three main classes of lipids. Cholesterol is one of the sterols, manufactured in the body for a variety of purposes
• Classification of Dietary Lipids

  • Saturated Fats
  • Unsaturated Fats
  • Monounsaturated Fats
  • Polyunsaturated Fats

  
• Saturated Fatty Acids (SFA)


  A fatty acid carrying the maximum possible number of H atoms (no double bonds between C atoms). Found in animal sources and some plant sources. Regular consumption may increase blood cholesterol levels and risk of CVD

  
• Unsaturated Fatty Acids


  A fatty acid with one or more points of unsaturation. Includes Monounsaturated Fatty Acids (MUFA) and Polyunsaturated Fatty Acids (PUFA)

  
• Monounsaturated Fatty Acids (MUFA)


  A fatty acid containing one point of unsaturation, found mostly in Olive oil and Hazelnut oil

  
• Polyunsaturated Fatty Acids (PUFA)

  A fatty acid in which two or more points of unsaturation occur, found in nuts, vegetable oils and fatty fish
• Essential Fatty Acids (EFA)


  Linoleic Acid (omega-6) and Alpha Linolenic Acid (omega 3). Cannot be synthesised in the body, important for brain, eye, skin health and foetal/infant development

  
• Omega-3 Fatty Acids


  • Mainly found in cold water fish, dissolve blood clots, lower blood pressure, dilate arteries, anti-inflammatory

  
• Omega-6 Fatty Acids


  • Mainly found in vegetable and nuts oil, important for growth, immune response, nervous system, pro-inflammatory
• Liquid vs Solid


  The more saturated a fat is, the more solid it is at room temperature (except palm and coconut oil) and vice versa - except fish

  
• Characteristics of Fats in Foods

  • Visible Fats
  • Invisible Fats

  
• Lipids


  • Susceptible to light, heat, air, moisture, long storage - oxidation
  • Affects quality, deteriorates flavour/taste/smell, causes bitterness
  • Decreases shelf life - Rancidity
• Antioxidants


  Vitamin C & Vitamin E prevent rancidity
• Polymerisation of Fats/oils


  All commonly used fats tend to form larger molecules (polymers) when heated under extreme conditions of temperature and time. Increases oil absorption, leads to undesirable odour/colour, brown gum-like structure

  
• Functions of Fats


  • Serve as an energy reserve
  • Major component of cell membranes
  • Nourish skin & hair
  • Insulate the body from temperature extremes
  • Cover vital organs to protect them from shock
  • Make up the myelin sheath surrounding the nerves for signal transduction
  • Provide satiety
  • Transport and absorption of fat-soluble vitamins & EFAs
  • Contribute to aroma & flavour – in food

  
• Trans Fatty Acids


  2 broad types: naturally-occurring and artificial. Artificial trans fats are formed when liquid vegetable oils are hydrogenated and solidified in an industrial process. Hydrogen molecules are on opposite sides of a double bond

  
• Trans Fatty Acids


  • Easy to use, inexpensive to produce, last a long time, give desirable taste and texture. But they clog arteries and lead to CVD, increase LDL cholesterol and decrease HDL cholesterol. Keep to minimum

  
• Frying oil


  Can be used more than once depending on the food type, frying time and duration and storage conditions. Filter out and store in a dark container in the refrigerator away from light, heat, moisture and O2. Don't use if foamy, sticky or dark in colour
• Phospholipids


  A water-soluble head + a fat-soluble tail + a phosphorous. Component of cell membranes, serve as emulsifiers (allow fats and water to mix and travel in and out of cells)
• Emulsification


  The process by which a system comprising of two immiscible liquids (e.g. oil and water), one of which is dispersed as small droplets within the other, is produced. Most commonly used emulsifiers are egg/soy lecithin
• Cholesterol


  A sterol, found only in animal products, also made & used in the body. Structure of cell membranes, used to make bile, hormones, vitamin D. High amounts are implicated in diseases
• Diseases caused by High Cholesterol

  • Atherosclerosis, High blood pressure, Heart attack, CVD and Coronary Heart Disease, Stroke, Death
• High Density Lipoprotein (HDL)


  "Good" cholesterol, helps remove cholesterol from artery walls and transport it to liver for elimination, high levels lower risk of heart attack
• Low Density Lipoproteins (LDL)


  "Bad" cholesterol, causes build-up of cholesterol in arteries, high levels increase risk of heart disease, primarily responsible for depositing cholesterol within arteries
• Fat Digestion


  1. Digestion

  2. Emulsification (with Bile)

  3. Absorption
• Lowering Blood Cholesterol Levels

  • Choose lean meats or fish
  • Use fat-free or low-fat milk products
  • Limit snack foods, bakery products and fried foods high in saturated fat and trans fats
  • Have fish twice a week – one should be oily (tuna, salmon, mackerel etc.)
  • Try to use vegetable oils (esp. olive oil) in cooking
  • Steam, boil or bake foods instead of frying
  • Don't forget to EXERCISE!

  
• Lipids are susceptible to factors such as light, heat, air, moisture, long storage -oxidation
• These affect the quality of lipids, deteriorate the flavour/taste/smell and cause bitterness
• Their shelf life decreases -Rancidity
• Rancidity


  Vitamin C & Vitamin E are antioxidants = prevent rancidity
• All commonly used fats tend to form larger molecules (polymers) when heated under extreme conditions of temperature and time
• Polymerisation increases oil absorption of foods, leads to undesirable odour/colour formation and a brown gum-like structure in the pan
• Functions of Fats


  Serves as an energy reserve
• Functions of Fats


  Major component of cell membranes
• Functions of Fats


  Nourishes skin & hair

  • Insulates the body from temperature extremes