Fats and Cholesterol

Presented by Janice Hermann, PhD, RD/LD

OCES Adult and Older Adult Nutrition Specialist

Chemistry of Fatty Acids and TriglyceridesLike carbohydrates, fatty acids and

triglycerides are composed of carbon (C), hydrogen (H) and oxygen (O).

These lipids have many more carbons and hydrogen’s in proportion to their oxygen’s; however, and so they supply more energy per gram.

Fatty AcidsA fatty acid is an organic acid-a chain of

carbon atoms with hydrogens attached, it has an acid group (COOH) at one end and a methyl group (CH3) at the other end.

There are over forty different fatty acids

Chain LengthMost fatty acids contain even numbers of

carbons in the chains, up to 24 carbons in length.Long-chain (12 to 24 carbons) fatty acids in

meats, fish and vegetable oils are most common in the diet

Medium –chain (6 to 10 carbons) are less common

Short-chain (fewer than 6 carbons) fatty acids occur, mostly in dairy products

Degree of SaturationFatty acids can be saturated or unsaturated.

A saturated fatty acids has all the carbons in the chain filled with hydrogen’s.

An unsaturated fatty acid is missing hydrogen’s, and as a result the carbons bond to each other twice, forming what is called a double bond.One place in the fatty acid missing hydrogen’s the

fatty acid is monounsaturated.Two or more places in the fatty acid missing

hydrogen’s the fatty acid is polyunsaturated.

Monounsaturated Fatty Acid

Polyunsaturated Fatty Acid

Saturated Fatty Acid

Location of Double BondsFatty acids are identified by the position of

the double bond nearest the methyl (CH3) end.

A polyunsaturated fatty acid with its first double bone three carbons away fro the methyl end is an omega-3 fatty acid.

An omega-6 fatty acid is a polyunsaturated fatty acid with its first double bond six carbons away from the methyl end.

Essential Fatty AcidsThe body can make saturated fatty acids

and the body can convert some saturated fatty acids into monounsaturated fatty acids.

The body cannot make two polyunsaturated fatty acids, linoleic acid (omega-6) and linolenic acid (omega-3), and therefore these are essential and must be provided from the diet.

TriglyceridesFats in our body and in food are made up of

fatty acids and glycerol called triglycerides.Glycerol is a water soluble compound that

can bind to three fatty acids.Monoglyceride – one fatty acid on glycerol.Diglyceride – two fatty acids on glycerol.Triglyceride – three fatty acids on glycerol.

Solid or Liquid FatsThe relative amounts of different fatty acids

effects whether a fat is solid or liquid.Unsaturated fats tend to be liquid at room

temperature and contain more unsaturated fatty acids.

Saturated fats tend to be solid at room temperature and contain more saturated fatty acids.

Exceptions are tropical oils, such as palm oil, palm kernel oil, cocoa butter and coconut oil. Even though these fats are liquid at room temperature they are very saturated.

Fats in Food

Foods contain combinations of the three types of fatty acids.

Completely saturated fats and completely polyunsaturated fats are rare in nature.

The dominate fatty acid in a food determines whether the fat is refereed to as saturated or unsaturated.

Modifying FatsIn food processing polyunsaturated fats

maybe modified.Hydrogenation makes liquid polyunsaturated fats

more solid and more saturated.Saturated fats are less susceptible to oxidation

and thus are more stableSaturated fats are more solid and thus more

pliable

Modifying FatsIn the process of hydrogenation not all

unsaturated fatty acids are hydrogenated.Hydrogenation changes some remaining

unsaturated fats from a “cis” (same side) to a “trans” (opposite side)

Trans fatty acids function more like saturated fats and thus may increase the risk of heart disease.

Chemistry of PhospholipidsPhospholipids have a glycerol backbone with

fatty acids attached at two of the three sites and a phosphate group attached to the third site.

The phosphate group is a water-soluble group and the fatty acids are fat-soluble groups. This allows phospholipids to dissolve in both water and fat.

Phospholipids in the BodyBecause phospholipids can dissolve in both

fat and water they:Are an important structural part of cell

membranes.Help fats and fat like compounds, such as fat

soluble vitamins and hormones, to move across cell membranes.

Act like emulsifier and help keep fat and fat like compounds dispersed in the blood which is water based.

Phospholipids in FoodLecithin is on the best known phospholipidsIn foods lecithin keeps fat particles

dispersed in water, such as salad dressings and mayonnaise.

Lecithin is an emulsifier found naturally in many foods; eggs, soybeans, and peanuts.

Phospholipids in the BodyPhospholipids are important in the body.

Phospholipids are in cell membranes to help fats and fat like compounds such as fat soluble vitamins and hormones move across cell walls.

Phospholipids also help keep fat and fat like compounds dispersed in the blood which is water based.

The body can make lecithin in the liver.

Chemistry of SterolsSterols are multiple-

ring structures.Cholesterol is one of

the best known sterols.

Both plant and animal foods contain sterols, but only animal foods contain cholesterol.

Cholesterol

The body needs cholesterol every day.Cholesterol serves as the starting material

for many important body compounds.Bile acidsHormones Vitamin DCell membranesMyelin sheath around nerve fibers

Cholesterol

The liver makes cholesterolThe liver makes 800 to 1500 mg of cholesterol

every day, much more cholesterol than in food.In healthy people the body makes less

cholesterol if dietary intake is high, and it more cholesterol if dietary intake is low.

Dietary saturated fat intake effects cholesterol synthesis more than dietary cholesterol.

DigestionLipids are not water soluble and digestive

are, this makes digestion of lipids more difficult.

MouthLittle fat digestion occurs in the mouthSolid fats melt when reach body temperatureAn enzyme is released by salivary gland at base

of tongue that has a major role in fat digestion for infants.

DigestionStomach

The churning of the stomach helps disperse fat into smaller droplets which helps expose fat to attack by the gastric lipase enzyme, an enzyme that performs best in the acidic environment in the stomach.

Still, little fat digestion takes place in the stomach.

DigestionSmall intestine

Fat in the small intestine triggers the release of cholecystokinin which signals the gallbladder to release bile

Bile acts an emulsifier and disperses fat so pancreatic and intestine lipases can work

Lipases remove the fatty acids from triglycerides leaving monoglycerides, free fatty acids and glycerol.

Lipases remove fatty acids from phospholipids.Sterols remain unchanged.

Fat Digestion

Fat Digestion

BileTwo things can happen to bile after it has

emulsified fat.Most bile is reabsorbed from the intestine and

recycled.Some bile can be bound to fibers in the large

intestine and excreted.Because cholesterol is needed to make bile,

excretion of bile effectively reduced blood cholesterol.

Bile

AbsorptionLipid digestion products are absorbed by cells

in the small intestine wall.From the intestine, glycerol, short-chain fatty

acids and medium chain fatty acids are released into the bloodstream.

The blood carries these lipids to the liver.

AbsorptionIn the intestine, larger monoglycerides and

long-chain fatty acids reform triglycerides.Phospholipids reform inside the intestine.In the intestine, triglycerides, phospholipids

and sterols (cholesterol) are packaged into a carrier called a chylomicron.

Chylomicrons are released into the lymph system which enters the bloodstream near the heart. The blood carries chylomicrons to body cells where lipids are removed.

TransportLipids are transported in the blood in lipid-

protein carries called lipoproteins. The lipids are packed in the center and

surrounded by proteins which are water soluble and allow transport in the water based blood.

ChylomicronsChylomicrons formed in the intestine

They carry lipids, mostly triglycerides, from the intestine to the body.

As cells remove triglycerides the chylomicrons get smaller. After most of the triglycerides have been removed and only protein, cholesterol and phospholipid remnants remain.

Special protein receptors on liver cell membranes recognize and remove the chylomicron remnants from the blood.

VLDLThe liver is an active site of lipid synthesis.

The liver uses glycerol and short-chain and medium-chain fatty acids from the blood; as well as carbohydrates, proteins and alcohol to make new triglycerides, cholesterol, phospholipids and other compounds.

Newly formed lipids are packaged into a carrier called VLDL (very low density lipoprotein) and released into the bloodstream.

VLDLVLDL has a high triglyceride and low

cholesterol concentration. As the VLDL is carried through the blood,

body cells remove triglycerides, causing the VLDL to get smaller.

The VLDL picks up cholesterol from other lipoproteins, and the proportion of lipids shift to more cholesterol.

Eventually the VLDL becomes a low-density lipoprotein (LDL).

LDLLDL has a high cholesterol content and low

triglyceride content.As the LDL is carried through the blood

body cells remove cholesterol and phospholipids to build new membranes, make hormones or other compounds, or store them for later use.

LDL receptors on the liver help remove LDL from circulation.

HDLThe liver makes another carrier called HDL. HDL is released from the liver and moves

through the blood picking up cholesterol and phospholipids from body cells and returning them to the liver to be removed.

Total, LDL, and HDL CholesterolTotal blood cholesterol is a measure of

cholesterol in both LDL and HDL.Cholesterol in the LDL is going out into the

body and increases risk of heart disease.Cholesterol in the HDL is going back to the

liver to be removed and decreases risk of heart disease.

Lipid Transport

MetabolismStoring triglycerides as triglycerides

Because fat provides twice the energy as carbohydrate and protein it is an efficient energy storage.

Unlike glycogen, the body can store an unlimited amount of fat. Unlike most body cells, which store only limited amounts of fat, adipose cells can readily take up and store fat.

MetabolismEnergy stored as fat because fats are calorie

denseHalf the weight of fat as carbohydrate is needed

to provide the same amount of calories. Water is also stored with carbohydrates; further increasing weight.

The weight of stored energy is important in animals because they move around. Plants don't move around so weight of stored energy is not a problem.

MetabolismUsing Triglycerides for Energy

When the body needs energy an enzyme, hormone-sensitive lipase, inside the adipose cells responds by dismantling stored triglycerides and releasing the glycerol and fatty acids into the blood.

Cells needing energy absorb these compounds and take them through a series of chemical reactions yielding energy, carbon dioxide and water.

Using Lipids for Energy

Functions of FatFats have many functions in our body.

Part of cell membranes and component of many body compounds.

Body fat protects internal organs and provides insulation from heat loss.

Source of fat-soluble vitamins and essential fatty acids.

Concentrated source of stored energy.

Functions Essential Fatty AcidsFrom the essential fatty acids the body can

make other polyunsaturated fatty acids that:maintain the structure of cell membranesmake eicosanoids that regulate:

blood pressureblood clottingblood lipidsimmune response to injury and infection

Health Effects of LipidsAlthough fat is important, but too much fat

increases the risk for chronic disease.High saturated fat and trans fat intakes are

associated with increasing blood cholesterol and heart disease.

High dietary cholesterol intake is also associated with increasing blood cholesterol and heart disease, although its effect is not as strong as saturated fat or trans fat.

Plaque Development

Health Effects of LipidsReplacing saturated and trans fats with

monounsaturated and polyunsaturated fats can help lower heart disease risk.

Consuming fish on a regular basis as a source of omega-3 polyunsaturated fatty acids may also lower the risk of heart disease by helping to prevent blood clots and protect against irregular heartbeats and lower blood pressure.

Health Effects of Lipids

High fat diets have also been associated with increased risk of certain types of cancers.

The relationship between fat intake and cancer is not clear, and may be more related to total calorie intake and obesity.

Health Effects of LipidsFat provide more than twice as many calories

as carbohydrate or protein. As a result, people who consume high fat diets may exceed their calorie needs resulting in weight gain and obesity.

By increasing the risk of obesity, high fat diets may indirectly increase risk of diabetes and high blood pressure.

Recommended Fat IntakeDefining the exact amount of fat, saturated

fat or cholesterol that benefits health or begins to harm health, however, is not possible; for this reason, no RDA or upper limit has been set

DRI for FatDRI recommends a diet low in saturated fat,

trans fat and cholesterol and provides 20 to 35% of the daily calories intake from fat.

The top end of this range is slightly higher than previous recommendations. This revision recognizes that diets with up to 35% of calories from fat can be compatible with good health if calorie intake is reasonable and saturated fat intake is low.

AI for Linoleic AcidThe AI for linoleic acid is 5 to 10% of calories

Men: 19-50 yr 17 g/dayMen: 51+ yr 14 g/dayWomen: 19-50 yr 12 g/dayWomen: 51+ yr 11 g/day

AI for Linolenic AcidThe AI for linolenic acid is 0.6 to 1.2% of

caloriesMen: 1.6 g/dayWomen: 1.1 g/day

Dietary GuidelinesConsume less than 10 percent of calories

from saturated fatty acids and less than 300 mg/day of cholesterol, and keep trans fatty acid consumption as low as possible.

Keep total fat intake between 20 to 35 percent of calories, with most fats coming from sources of polyunsaturated and monounsaturated fatty acids, such as fish, nuts, and vegetable oils.

Dietary GuidelinesWhen selecting and preparing meat,

poultry, dry beans, and milk or dairy products, make choices that are lean, low-fat, or fat-free.

Limit intake of fats and oils high in saturated and/or trans fatty acids, and choose products low in such fats and oils.

Lowering Fat IntakeLowering fat intake does not mean omitting

meats and dairy foodsLower fat intake by choosing lean meats and

dairy foods, using low-fat preparation methods, limiting the use of added and hidden fats, and watching portion size.