Lipids: Not Just Fat BIOL 103, Chapter 6. Today’s Topics What are Lipids? Fatty Acids are Key...

Lipids: Not Just Fat

BIOL 103, Chapter 6

Today’s Topics

• What are Lipids?• Fatty Acids are Key Building Blocks• Triglycerides• Phospholipids• Sterols• Lipids Digestion and Absorption• Lipids in the Body• Lipids in the Diet• Lipids and Health

Lipids

• Essential nutrients• Provide energy• Help transport fat-soluble nutrients• Contribute to flavor and texture of food

What are Lipids?

• Lipids include…– Triglycerides (most abundant lipids)

• In body: stored in adipose tissue• In food: “fats and oils”

– Phospholipids (~2% of dietary lipids)• Plant and animal origin• Body can make them• Soluble in fat and water

– Sterols (very, very small % of lipids)• Most well known: Cholesterol

Fatty Acids are Key Building Blocks

• Fatty Acids – Determine whether a fat is solid or liquid at room

temperature– Basic structure: (-COOH); (-CH3)

• Chain length– 2-24 Carbon length

Fatty Acids are Key Building Blocks

• Saturation– Saturated fatty acids

• All single bonds between carbons– Unsaturated fatty acids

• One or more carbon bonds is a double bond1. Monounsaturated fatty acid (MUFA)2. Polyunsaturated fatty acid (PUFA)

– Fats with more double bonds are generally more liquidy

Saturated vs. Unsaturated Fatty Acids

Fatty Acids are Key Building Blocks

Cis fatty acids• Occurs naturally• Chain is bent

Trans fatty acids• Produced by hydrogenation

(adds hydrogen to an unsaturated fatty acids)

• A small portion of trans fat can occur naturally

• Chain is straighter

Trans Fat

• In health, trans fatty acids are known to raise LDL (“bad”) cholesterol, and lower HDL (“good cholesterol”), promote systemic inflammation, and increase triglycerides in your blood.

• History and how it is made:– In Europe (1910)– In US (1960s)

Fatty Acids are Key Building Blocks

• Nonessential and essential fatty acids1. Nonessential fatty acids

• Can be made in the body• Not “essential” to have in your diet

Fatty Acids are Key Building Blocks

• Nonessential and essential fatty acids (cont.)2. Essential fatty acids

• Can’t be made in the body

• Must come from food• Omega-3 (alpha-

linolenic acid) and omega 6 (linoleic acid)

• Used to make eicosanoids

Triglycerides

• Structure– Glycerol + 3 Fatty Acids

• Functions1. Energy source: 9 kcal/g2. Energy reserve: form of stored energy in adipose tissue

(“fatty tissue”)3. Insulation and protection:

1. Visceral fat (fat around organs)2. Subcutaneous fat (fat under skin to protect/insulate body)

4. Carrier of fat-soluble nutrients5. Sensory qualities in food

Apple vs. Pear

Triglycerides in Food

• Found in a variety of fats and oils• Classified by their most prevalent type

– Saturated fatty acids: animal foods and tropical oils

– Polyunsaturated fatty acids: plant or animal based• Omega-3: soybean, flaxseed oils; salmon, tuna• Omega-6: seeds, nuts, corn oil, meat, poultry, eggs

What are the positive and negative consequences of hydrogenating a fat?

(Problem Set 6, #3)

Pros Cons

• Oxidation causes food to spoil and damage body tissues

Phospholipids

• Structure– Glycerol + 2 fatty acids + phosphate

group• Functions:

1. Emulsifiers• Keep fat suspended in water• Keep oil and water mixed

2. Structural element for cell membranes

Phospholipids

• Cell membrane– Double layer of

phospholipids– Store fatty acids

temporarily and release them as needed can regulate them closely

– Important role in nerve cells

• e.g. Ach

Phospholipids

• Lipid transport– Stomach

• Breaks fat into tiny particles for digestion (i.e. lingual lipase)

– Intestine• Continues emulsifying fat (i.e. bile)

– Blood• Coat the surface of the lipoproteins that carry lipid

particles to their destinations in the body

Phospholipids

• Emulsifiers (Lecithin)– In body

• Phospholipid with choline phosphotidylcholine

– In food• Blend of phospholipids

with different nitrogen-containing components

• Used as emulsifiers (e.g. salad dressing, chili, sloppy-joe mixes, and chewing gum).

Phospholipids

• Phospholipids in food– Occur naturally in plants and animals– Examples: Egg yolks, liver, soybeans, peanuts– Not dietary essential because the body can make

it

Sterols

• A category of lipids that include cholesterol

• Structural characteristics:– Multiple ring structure– Contain no fatty acids

Sterols

• Cholesterol functions:1. Structural component of cell membranes2. Precursor to other substances

• Examples: Vitamin D, Sterol Hormones, Manufacture bile salts

• Cholesterol synthesis in liver• Sterols in food

– Found only in animal foods

Lipid Digestion

• Digestion of triglycerides (TG), cholesterol, and phospholipids (PL)– Mouth

• Chewing + lingual lipase

– Stomach• 30% Triglycerides + gastric lipase FFA and DG

Lipid Digestion (cont.)

• Small Intestine– Emulsified by bile – Rest of the “exposed” TG and DG are digested by

pancreatic lipase – Phospholipids digested by pancreatic

phospholipase – Cholesterol ester digested by cholesterol esterase– Bile salts surround digested fat and form micelles

Lipid Absorption

Lipid Digestion (cont.)

• Micelles carry digested fat through the watery environment to microvilli/small intestine– The lipid components are then absorbed into the

intestinal cells at the microvilli– Bile salts return to the liver to be used again

• Short-chain FA and glycerol are directly absorbed into your intestinal cells without the help of micelles.

Lipids Absorption

• To travel in the bloodstream, lipids are packaged into lipoprotein carriers

• How? – In your intestinal cell: MG + FFA rejoin TG

• Cholesterol esters and phospholipids form here also

– Then, TG, PL, cholesterol esters join protein carrier lipoprotein.

– Lipoprotein leaves the intestinal cell chylomicron goes to lymph system bloodstream.

Lipid Digestion and Absorption(Figure 6.21)

Chylomicron Transport

• In the blood stream, chylomicrons are large, fatty lipoproteins (90% fat) circulate in the body while releasing TG

• When reaching capillaries, lipoprotein lipase “attacks” chylomicrons to remove TG FFA and glycerol:– FFA enter adipose cells reassembled into TG– OR FFA enter muscle cells used for energy– Glycerol liver or kidney

• Your liver picks up “left-over” chylomicron and uses them to build VLDL

Lipids in the Body1. Very-low-density lipoproteins (VLDL):

– Deliver triglycerides to cells

2. Intermediate-density lipoproteins (IDL) – Returns to liver and is converted to LDL

3. Low-density lipoproteins (LDL)– Deliver cholesterol to cells, which body uses to

synthesize membranes, hormones, etc.– Returns to liver afterwards

4. High-density lipoproteins (HDL)– Pick up cholesterol for removal or recycling

Lipoprotein Pathway Summary

Lipoprotein density

• Lipoproteins differ by size, density, and composition of their lipid cores– In general, larger the lipoprotein, the less dense it

is.– Size: HDL < LDL < IDL < VLDL < Chylomicron

Problem Set 6, Q#4:

• Describe the differences between LDL and HDL and protein composition

Lipids in the Diet

• Recommended intake:– Reduce saturated fat and trans fat– Total fat: 20-35% of calories– Less than 10% of calories from saturated fat

Lipids in the Diet

• Essential FA requirements– Linoleic acid/omega-6 FA should provide about 2%

of calories– Requirements for omega-3 FA is less well-known

• Omega-6 and omega-3 FA balance– Ratio of 6:1 (omega-6 to omega-3 FA)– While omega-3 FA is good for you, consuming too

much of the omega-3 FA can suppress immune function and prolong bleeding time

Lipids and Health

• Following are examples are diseases associated to high intakes of saturated and trans fat.

1. Obesity– Determined by excessive accumulation of body fat leading to a body

weight in relation to height that is significantly greater than some accepted standard.

– High-fat diets promote weight gain

2. Heart Disease/Cardiovascular Disease– Leading cause of death in US (1 death/minute)– Major risk factors

• High blood cholesterol (High LDL, low HDL)• Smoking• High blood pressure

Lipids and Health

3. Atherosclerosis– Slow, progressive hardening and narrowing of

arteries– Promoted by high blood cholesterol

4. Inflammation and atherosclerosis– How? – Smoking, infection, or high blood pressure can

speed up this process described above

Atherosclerosis

AHA diet and lifestyle recommendations:

• Reducing heart disease risk (pg. 222-226)– Go over on your own1. Consume an overall healthy diet2. Aim for a healthy body weight3. Aim for a desirable lipid profile4. Aim for normal blood pressure5. Aim for normal blood glucose levels6. Be physically active7. Avoid use of and exposure to tobacco products

AHA diet and lifestyle recommendations (cont.):

• Reducing heart disease risk (pg. 222-226)8. Balance calorie intake and physical activity to

achieve or maintain a healthy body weight9. Consume a diet rich in fruits and vegetables10. Choose whole-grain, high fiber foods11. Consume fish, especially oily fish, at least

2/week12. Limit your intake of saturated and trans fat

AHA diet and lifestyle recommendations (cont.):

• Reducing heart disease risk (pg. 222-226)13. Minimize your intake of beverage foods with

added sugars14. Choose and prepare foods with little or no salt15. If you consume alcohol, do so in moderation16. Follow the AHA recommendations when eating

outside of the home

Metabolic Syndrome

• ¼ US adults has metabolic syndrome• Has at least 3 of the following symptoms:

1. Excess abdominal fat2. High blood glucose3. High serum triglycerides4. High blood pressure5. Low HDL cholesterol

Putting it all together

• Healthy People 2020 objectives target:1. Reducing deaths from heart disease and stroke 2. Reducing the number of adults with high blood

cholesterol levels

Cancer

• Stages of development: – Initiation: a mutation in cell’s genetics abnormal

cell– Promotion: when a chemical (e.g. carcinogen)

encourages initiated cells to become active• Reversible stage

– Progression: when promoted cells multiply and invade healthy tissues

Cancer (cont.)

• Dietary and lifestyle factors for reducing cancer risk:

1. Maintain a healthful weight2. Adopt a physically active lifestyle3. Consume a healthy diet4. If you drink alcohol, limit consumption