unit 5 lipids review

the functions of fats in the body

1. Storing energy

• Potentially large, calorically-dense, long-term energy storage

2. Insulating and protecting

• Visceral fat – within abdominal cavity – protects vital organs

• Subcutaneous fat – under skin – insulates, pads

3. Regulating and signaling

• Hormone production

• Reproductive health

• Regulate cholesterol, blood clotting, inflammation

• Nerve impulse transmission

• Cell membranes

the functions of fats in the diet

1. Aid absorption and increase bioavailability

• Fat-soluble vitamins, phytochemicals

2. Contribute to the taste, smell, satiety value of

foods

• Satisfy appetite (desire to eat) by adding

flavor

• Satisfy hunger (need to eat) by slowing

digestion and absorption

3. Provide essential fatty acids

• Fatty acids that can’t be synthesized in the

body

lipids

are a family of molecules that don’t mix well with water

triglycerides

• Main form of lipid in the diet

and body

• When we talk about “fat” in the

body and food, we are talking

about triglycerides

• Main type of lipid in food and the body

• 3 fatty acids on a glycerol backbone

• Can contain different types of fatty acids

phospholipids

• structure is both fat and water-soluble

• Similar in structure to triglycerides

• 2 fatty acids + 1 phosphate group on a glycerol backbone

sterols

• Multi-ring organic molecules

• Cholesterol is the main sterol in animals

  • Not an essential nutrient, because we can synthesize it

  • Only found in foods from animals (meat, poultry, eggs, fish, butter, dairy)

• Functions of cholesterol:

  • Precursor to vitamin D, bile, hormones

  • Part of cell membrane structure

• Plant sterols are found in plant-derived foods (vegetable oils, nuts, seeds, whole grains) and can inhibit cholesterol absorption

3 main types of lipids

• triglycerides

• phospholipids

• sterols

amphiphilic (phospholipids)

• = both fat- and water-soluble

  • This makes them very useful!

• Functions:

  • Cell membranes

  • Lipid transport

  • Emulsification of food

fatty acid types

There are many types of fatty acids. They differ in

•chain length (2 to 24 carbons)

•degree of saturation (# of double bonds)

foods contain a mixture of fatty acids

• Triglycerides can contain different proportions types of fatty acids.

• A given food or fat source contains a mixture of all 3 categories.

• Foods are often classified based on their predominant fatty acid type. For example:

  • Coconut oil is sometimes referred to as a saturated fat since it predominantly contains saturated fatty acids.

  • Olive oil is similarly referred to as a monounsaturated fat.

saturated fats

• No C=C double bonds; all C’s are saturated with H’s

• Pack together well → solid at room temperature

• Food sources: Animal fats, dairy products, coconut oil, palm kernel oil

• Health effects: May increase risk of heart disease if in excess

monounsaturated fats

• 1 C=C double bond; one point of unsaturation

• Bent structure → liquid at room temperature

• Food sources: canola, olive, peanut oils; avocados, almonds, pecans, sesame seeds

• Health effects: May decrease risk of heart disease

polyunsaturated fats

• 2+ C=C double bonds; multiple points of unsaturation

• Bent structure → liquid at room temperature

• Food sources: sunflower, safflower, soybean, corn oils; fish, flax, and walnuts

• Health effects: May decrease risk of heart disease

omega-3 and omega-6

Polyunsaturated fatty acids are omega-3 or omega-6 depending on the position of the first double bond from the omega end

essential fatty acids

There are 2 essential fatty acids, which must be consumed in the diet

• Linoleic acid (omega-6), found in vegetable oils like corn and soybean oils

• Alpha-linolenic acid (omega-3), found in nuts, flax, whole grains, legumes, and dark green leafy veggies

digestion and absorption of lipids

• Triglycerides are large, water-insoluble molecules that require some special handling for digestion and absorption

• Enzymatic digestion by lipases in the mouth, stomach, and especially the small intestine

• Emulsification by bile in the small intestine to break large fat globules into smaller droplets to increase surface area for enzymatic digestion

chylomicrons

• transport lipids from intestine to bloodstream

• are a type of lipoprotein - lipid transport vehicles

structure of lipoproteins

allows lipids to move through aqueous environment of the body

chylomicrons (lipoproteins)

transport lipid from the small intestine and deliver triglycerides to the body’s cells (bloodstream)

VLDL (lipoproteins)

are large and low density and deliver triglycerides from the liver to the body’s cells

LDL (lipoproteins)

are formed from VLDL after removal of most triglycerides; they deliver cholesterol to the body’s cells

HDL (lipoproteins)

are the smallest and most dense lipoproteins; they clean up cholesterol and deliver it to the liver for disposal

understanding blood cholesterol values

• Blood cholesterol or lipid panel values report total cholesterol, LDL, HDL, and triglycerides.

• There is no “good cholesterol” or “bad cholesterol” in food; cholesterol is just cholesterol.

• In blood, LDL is considered “bad cholesterol,” because too much LDL in the blood can cause formation of plaques in artery walls, leading to atherosclerosis and increased risk of cardiovascular disease.

• Increasing physical activity, lowering saturated fat intake, and stopping smoking can help lower LDL. Medications such as statins are also used to treat high LDL.