Chapter 6: Lipids

Lipids

a type of macronutrient

• triglycerides (fats)

• fatty acids

• sterols

• and phospholipids

Fatty Acids

• hydrocarbon chains

• provide energy for cells

• components of triglycerides and phospholipids

• can be short-chain (2-4 C), medium-chain (6-12 C), long-chain (14-24 C)

Fatty Acid Saturation

Fatty acids can be saturated or unsaturated

monounsaturated fats

1 double bond

polyunsaturated fat

2 or more double bonds

unsaturated fats

has one or more double bonds

saturated fats

no double bonds, saturated with Hs

Essential Fatty Acids

Must be obtained from the diet because the body cannot synthesize them in sufficient amounts.

• Two main types: alpha-linolenic acid (omega-3) and linoleic acid (omega-6).

two types of polyunsaturated fatty acids

alpha-linolenic acid & linoleic acid

alpha-linolenic acid

• omega-3 fatty acid- first double bond after 3rd carbon 

• used to make 2 other omega-3 FA

  • eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)

linoleic acid

• omega-6 fatty acid

• converted into arachidonic acid (AA)

EPA, DHA, AA

used to make hormone-like substances such as prostaglandins

• good sources of both EFAs- canola, vegetable, or soybean oils, fatty fish, whole grains 

Benefits of Omega 3 Fatty Acids

• may reduce risk of heart attack/stroke

• reduces inflammation, blood triglycerides, and blood clotting

Trans Fats

• cis fatty acids have a bend at the C=C

• trans fatty acids do not- Hs on opposite sides

• small amount naturally found in whole-milk products, butter, and meat

• trans fats raise “bad” cholesterol levels increased risk of heart disease

• artificial trans fat = result of partial hydrogenation- adding hydrogen atoms to unsaturated fatty acids = turns liquid to solid fat

hydrogenation

adding hydrogen atoms to unsaturated fatty acids = turns liquid to solid fat

• better shelf-life

  • banned in 2021 due to health risks

  • often replaced with fully hydrogenated oils = saturated fat

Triglycerides

• made up of 3 fatty acids + glycerol

• often referred to as fats and oils

• used for energy and stored as fat

• most foods have a mixture of saturated and unsaturated fatty acids

• fats/oils with high amounts of saturated or unsaturated fatty acids are often called saturated or unsaturated fats

Fats vs. oils

both- triglycerides containing fatty acids

• fats- solid at RT (more saturated FA)

• oils- liquid at RT (more unsaturated FA)

Fats and Health

• diets high in saturated and trans fat > increased risk of cardiovascular disease

• diets high in unsaturated fats (especially omega-3) = lowered risk of CVD

Phospholipids

a major part of the cell membranes of our cells, also found naturally in food

• like triglycerides, except they have only 2 fatty acids and the third is replaced with a phosphate group

• lecithin is the main phospholipid in food

  • good sources of lecithin- egg yolks, liver, wheat germ, peanut butter, soybeans

  • contains choline, which nerves use to make the neurotransmitter acetylcholine

• partially water soluble because they contain hydrophobic and hydrophilic regions, so they can act as emulsifiers- keep water-soluble and water-insoluble things mixed (prevents separation of oily and watery ingredients)

emulsifiers

keeps water-soluble and water-insoluble things mixed (prevents separation of oily and watery ingredients)

Sterols

made of rings of carbon

• plants make phytosterols and phytostanols

  • compete with cholesterol for absorption in the GI tract

  • added to some foods/supplements to lower cholesterol levels in blood

cholesterol

found only in animal foods, but the body can also make it

• important part of cell membranes

• used to make substances such as vitamin D, and steroid hormones (estrogen, testosterone)

  • used to make bile

  • excess cholesterol associated with CVD

Lipid Digestion

• saliva secretes inactive lipase that gets activated in the stomach to start lipid digestion

• in sm. intestine the hormone cholecystokinin (CCK) stimulates the gallbladder to release bile, which contains bile salts to keep lipids dispersed and forms them into droplets called micellese (increases surface area for digestion)

• triglycerides and phospholipids get broken down into their components (glycerol and fatty acids) 

micellese

Tiny spherical complexes of emulsified fat that arise during digestion.

Lipid Absorption

• micelles —> sm. intestine villus —> absorption of monoglycerides, free fatty acids, and cholesterol

• short and medium-chain fatty acids directly to bloodstream

• long-chain FA, glycerol, monoglycerides, phospholipid parts are reassembled into triglycerides and phospholipids

• cholesterol and triglycerides are coated with a thin layer of protein, phospholipids, and cholesterol to form chylomicrons, a type of lipoprotein- transport lipids through bloodstream (water-soluble)

• lipoprotein lipase in the capillary walls breaks down chylomicron contents; cells absorb

Bile Salt Recycling

• most bile salts are reabsorbed and used by the liver to make new bile- enterohepatic circulation

• plants contain soluble fiber that can interfere with cholesterol and bile absorption  reduces blood cholesterol levels

Triglycerides as an Energy Source

• most cells can use fatty acids for energy (9 Cal/g)

• If the energy from fat isn’t needed, adipose cells (fat cells) take up fatty acids and glycerol and reassemble them into triglycerides storage

• When energy is needed adipose cells break down triglycerides release into bloodstream, FA used for energy, liver converts glycerol glucose for energy

• consumption of too many Calories (from any source) converted into triglycerides excess body fat

• alcohol also stimulates triglyceride synthesis

Lipid Consumption Patterns

• Dietary Guidelines = 20-35% of total Calories from fat, including mono- and polyunsaturated fatty acids

• adults should consume less than 10% of Calories from saturated fatty acids

• consumes as little cholesterol and trans fats as possible

• Americans are a little above those guidelines

Nutrition Labels

• required to list total fat, saturated fat, trans fat, and cholesterol

• many also list mono- and polyunsaturated fat

• remember that <0.5g of any type of fat can be listed as zero- read ingredients!

Cardiovascular Disease (CVD)

medical conditions related to the heart and blood vessels

• heart disease (CAD) and stroke are most common and are one of the top causes of death in the U.S.

  • Coronary Artery Disease (CAD)

  • carotid artery disease

  • peripheral artery disease

carotid artery disease

affects arteries in the neck & brain

Coronary Artery Disease (CAD)

aka heart disease

• affects arteries that bring blood to the heart = heart attack

peripheral artery disease

affects arteries that go to limbs/pelvis 

Heart Disease

most often due to atherosclerosis- plaque build up inside arteries

• when the lining of an artery is irritated (due to excess cholesterol or glucose, cigarette smoke, etc), inflammation & cells deposit cholesterol under arterial lining as it heals — arterial plaque — decreased circulation due to narrowed or blocked vessels and rougher surface = clots more likely to form

• ruptured plaque —> to clot formation to heal, can be life-threatening

• thrombus- bunch of clots that disrupts blood flowc heart attack, stroke, or gangrene in limbs

• thrombus or plaque that breaks free: embolus

Other Affects of Atherosclerosis

• causes arteries to become stiff hypertension- chronic abnormally high blood pressure heart has to work harder to pump blood

• Hypertension = major risk factor for heart disease and stroke

Lipoproteins and Atherosclerosis

• 3 other types of lipoproteins besides chylomicrons- vary in proportions of protein, cholesterol, triglycerides, and phospholipids

• chylomicron- largest and least dense (mostly lipids)

• high-density lipoproteins (HDL)- smallest, most dense (mostly protein)

• low-density lipoproteins (LDL)- transport more cholesterol vs. HDL

• very-low-density lipoproteins (VLDL)- more triglycerides

Lipoproteins (cont.)

• HDL brings lipids to the liver for processing and elimination.

• cholesterol carried by HDL = “good”

• LDL brings lipids to tissues- “bad” because it is involved with plaque formation

• not as simple as “good” and “bad” because many factors can contribute:

  • “free radicals” and smoking cigarettes can damage cholesterol in LDLs, which is taken up by plaque-forming artery cells

  • some HDLs may transport damaged cholesterol as well

  • VLDL may contribute to atherosclerosis- more triglycerides may stimulate production of LDL

  • excess alcohol and refined carb. intake stimulates production of VLDL

Nonmodifiable vs. Modifiable Risk Factors for Atherosclerosis

• Some people with CVD have no risk factors- possibly linked with high levels of homocysteine (an amino acid)- possibly due to genetic defect or B vitamin deficiency 

Medical Testing

• blood pressure

• cholesterol

• triglycerides

• C-reactive protein- indicator of    inflammation

Alcohol and Your Health

• alcohol provides 7 Cal/g

• detoxification of alcohol starts  in the stomach, then the liver (which switches from macronutrient metabolism (detoxification), lungs and sweating get rid of some, kidneys filter some urine

• variability in how alcohol affects people- depending on food intake, sex, body size and composition, age, prior drinking history

• can develop tolerance

In Summary…

• Fatty acids, triglycerides, phospholipids, and sterols are all lipids that are needed in the body.

• Saturated and trans fats should be limited and unsaturated fats consumed in moderation.  

• Cardiovascular disease often causes atherosclerosis, which can lead to many other issues including hypertension, heart attack, stroke, and more.

• Alcohol is a drug that can negatively impact your nutrition and health in general.