Fatty Acids

• Carbon chain - chains of carbon; usually between 18 and 24 carbons long; containing an acid group (COOH) at one end - and a methyl group (CH₃) at the other.
• Triglyceride formation
  • formed through condensation and combination of one glycerol molecule attached to three fatty acids
  • chief form of fat in the diet and a major storage form of fat in the human body
• Saturation
  • chemically - refers to a structure carrying the maximum possible number of hydrogen atoms

Saturated fatty acids: completely loaded with hydrogren, no double bonds
Saturated fats - composed of triglycerides in which most of the fatty acids are saturated

Monounsaturated fatty acids: lacks two hydrogren atoms, contains one double bond
Monounsaturated fats - composed of triglycerides in which most of the fatty acids are monounsaturated

Polyunsaturated fatty acids: lacks four or more hydrogren atoms, contains two or more double bonds
Polyunsaturated fats - composed of triglycerides in which most of the fatty acids are polyunsaturated
 

Fats in Food

Processed fat

• fats become rancid when exposed to oxygen; oxidation occurs when double bonds are unstable
• to protect against oxidation, manufacturers seal products air-tight, add antioxidants, or saturate the fats at points of unsaturation (called hydrogenation)
  • Hydrogenation - hydrogens are added chemically to monounsaturated and polyunsaturated fats to reduce double bonds to protect against oxidation
  • Trans-fatty acids - fatty acids (produced in hydrogenation and sometimes naturally) with an unusual (trans) configuration around the double bond.  Trans fatty acids are found in: margarine, cakes, dairy, meat, potato chips, shortening

Roles of Triglycerides and Fatty Acids

• Provide Energy
• Provide an energy reserve in fat tissue
• Insulate against temperature extremes
• Protects organs against shock
• Helps body use carbohydrates and protein efficiently

Essential Fatty Acids (EFAs) - fatty acids needed that the body cannot provide for itself in sufficient quantities (must obtain through food)
 

1. Linoleic Acid
Primary omega 6 fatty acid and must be supplied by food
Needed for the body to synthesize arachidonic acid

2. Linolenic acid
Primary omega-3 fatty acid and must be supplied by food
Needed for the body to synthesize eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)
May prevent and treat heart disease, hypertension, arthritis, and cancer.

Fatty acid Deficiencies
Essential Fatty Acids (EFAs) deficiencies (although rare) may result in growth retardation, reproductive failure, skin lesions, kidney and liver disorders, and subtle neurological and visual problems. [TOP]
 

Lipid Digestion

In the mouth: sublingual salivary glands secrete lingual lipase
In the stomach: (fat floats above other food components)

• Lingual lipase may continue to hydrolyze one bond from triglycerides to form diglycerides and fatty acids
• Stomach churns and mixes fat with water and acid
• Gastric lipase hydrolyzes some fat (not much)

In the small intestine:

• CCK (cholecystokinin) signals gallbladder to release bile for emulsification of fat
• Pancreatic lipase enters from pancreas through the pancreatic duct - breaks down triglycerides to a monoglyceride or occasionally to a glycerol
• Intestinal lipase also acts on triglycerides with pancreatic lipase
• Bile is either reabsorbed and recycled or trapped by dietary fiber and excreted: if excreted, the liver must make more bile from cholesterol (effectively lowering blood cholesterol)

Lipid Absorption

• Some glycerol, short-chain fatty acids, and medium-chain fatty acids can be absorbed into the blood stream by diffusing the intestinal cells
• Monoglycerides and long-chain fatty acids merge into micelles (spherical shaped complexes) for transport through the microvilli of intestinal cells
• When micelles diffuse into intestinal cells - the monoglycerides and long-chain fatty acids are reassembled into triglycerides and carried away by chylomicrons

Lipid Transport

1. Chylomicrons

• largest and least dense lipoprotein
• transports diet-derived lipids (primarily triglycerides) from the intestine to the cells of the body

2. VLDL (Very Low Density Lipoproteins)

• made by the liver to transport liver-synthesized lipids (primarily triglycerides) to the cells of the body
• as it loses triglycerides, they collect cholesterol from other lipoproteins and become LDL

3. LDL (Low Density Lipoproteins)

• composed mostly of cholesterol
• carries and deposits cholesterol to tissue cells: muscle, fat stores, mammory glands, heart, etc...
• the liver can control the amount of LDL in circulation

4. HDL (High Density Lipoproteins)

• Smallest lipoprotein, is the most protein-dense lipoprotein
• carries cholesterol and phospohlipids from the cells back to the liver for recycling or disposal

Factors that improve LDL:HDL ratios:

• weight control
• monosaturated or polyunsaturated fatty acids in place of saturated fat
• soluble fiber
• antioxidants
• moderate alcohol consumption
• physical activity  [TOP]

Measuring Percent Body Fat

Fatfold measures (aka skinfold tests): estimate of body fatness based on a measurement by a caliper on thickness of a fold of skin over the triceps, below the shoulder blade, around the abdomen, and/or on the upper leg

Waist circumference: Measure of distance around the waist, typically over 35 inches for women and over 40 inches for men is associated with increased health risks.

Waist-to-hip ratio: Calculation of waistline measurement divided by hip measurement.  Women over 0.80 and men over 0.90 have higher risks of health problems.

Hydrodensitometry (hydrostatic weighing): Measures the body's density by comparing body weight to an additional weighing underwater.  Considered one of the most reliable methods.

Bioelectrical impedance: estimates body fat based on electrical resistance of a low-intensity electrical current

Air Displacement:  An enclosed egg-shaped shell uses computerized sensors to determine the amount of air displaced by a person's body when in the shell  [TOP]