Exercise Physiology - Lipids

Lipid Kinds and Sources

• synthesized by plants and animals

• three groups: simple (neutral fats), compound, derived

• simple: triacylglycerols (TAG), also known as triglycerides

• compound: phospholipids

• derived: cholesterol

Triaclyglycerols

• major storage form of fat in adipocytes (fat cells)

• contain one glycerol and three fatty acid chains

• include saturated, monounsaturated, polyunsaturated lipids

Saturated Fatty Acids

• carbon binds to the maximum number of hydrogens

• no double bonds; fatty acid chains fit close together

• occur primarily in animal products and some plants

• lead towards artieal issues

Unsaturated Fatty acids

• monounsaturated contain one double bond (olive oil, avocados, almond oil)

• polyunsaturated contain two or more double bonds (soybean and corn oil, omega - 3 oil)

Triaclyglycerol formation

1. fatty acid attaches to coenzyme A to form fatty acyl - CoA (acyl fatty acid), which then transfers to glycerol.

2. two additional fatty acyl - CoAs link to the single glycerol backbone to form triaclyglycerol.

3. triclyglycerol synthesis increases after a meal due to an increase in fatty acids and glucose and/or high levels of insulin.

What enzyme regulates Triaclyglycerol breakdown (Lipolysis)

Hormone - sensitive lipase (HSL)

When does lipolysis occur?

• low to moderate intense physical activity (demand isn’t extreme, vast energy source is lipids)

• low calorie diet/fasting (not getting energy from food, so you are burning fat (lipids) for energy)

• prolonged endurance activity when glycogen stores are depleted

• cold stress (shivering is low intensity energy depletion, contract muscles and use fat to stay warm)

Trans - Fatty acids: unwanted at any level

• derived from partial hydrogenation of unsaturated corn, soybean, or sunflower oil

• increases harmful low-density lipoprotein cholesterol (LDL) - influence plaque in arteries (blood hard to pump)

• decreases beneficial high density lipoprotein cholesterol (HDL) - breakdown and removes plaque

Compound lipids - phospholipids

fatty acid joined to phosphate group and nitrogen - containing molecule

What are the four major functions of phospholipids?

• interact with water and lipid to modulate fluid movement across cell membranes (help balance fluid in the body)

• maintain structural cell integrity

• play important role in blood clotting

• provide structural integrity to the insulating sheath surrounding nerve fibers

Lipoproteins (compound protein)

Major transport means for lipids

High density lipoprotein (HDL)

“good” cholesterol, removes cholesterol from arterial walls

Low-density lipoprotein (LDL)

“bad” cholesterol, bind to arterial walls

Very low density lipoprotein (VDL)

transport TAGS to muscle and adipose tissue

Chylomicrons

liver metabolites for storage and adipose tissue, transports vitamins A, D, E, and K

Derived lipid: Cholesterol

• liver synthesizes 70% of cholesterol but also ingested in diet

• important in building membranes

• precursor in synthesis of vitamin D, adrenal gland hormones, and sex hormones

• from animal sources only: egg yolks, red meat, shellfish, dairy

• cholesterol in your body is not the same as dietary cholesterol

roles of lipids

• energy source and reserve - carries large quantities of energy per unit weight, transports and stores easily, provides an available energy resouce

• protect vital organs (brain, heart, liver) from trauma

• thermal insulation

• vitamin carrier (chylomicrons) and hunger suppressor

Lipis dynamics during physical activity

• lipid supplies 40-80% of energy during physical activity

• primary energy source during light-moderate exercise is intramuscular triaclyglycerols and fatty acids

• during moderate-intensity activity, carbohydrates and lipids supply approximately equal amounts of energy (crossover point)

• during activity longer than one hour, lipid breakdown increases

effects of aerobic training

aerobic exercise training improves fatty acid oxidation during mild to moderate intensity exercise