Module 6: Lipids

How fatty acids are named

*Based on number of carbon atoms in chain and the location of the double bond(s) in the carbon chain.* - Mono-Unsaturated Fatty Acid (MUFA) - one C=C - Poly-Unsaturated Fatty Acid (PUFA) - many C=C - Cis = hydrogen atoms are on same side of C=C - Trans = hydrogen atoms are on opposite side of C=C Omega ω system (in English, lowercase "n" is sometimes used for ω) - Indicates first double bond closest to methyl (omega) end of chain Delta Δ system - Starts with the carboxyl end to indicate location for all double bonds CONCLUSION: - Saturation (or unsaturated) - Unsaturated: how many carbon double bonds? - MUFA/PUFA - Unsaturated: direction of hydrogen atoms next to carbon double bond - cis/trans - Unsaturated: which end of the carbon chain to start counting carbons? - omega or delta

Basic chemical structure of fatty acids

*Chain Length:* - Long chain fatty acids (LCFA) = 12 or more carbons - Medium chain fatty acids (MCFA) = 6 - 10 carbons - Short chain fatty acids (SCFA) = less than 6 carbons

How are fats carried in the blood?

*Fat is transported in lipoprotein particles to the blood.* Shell composed of: - Phospholipids - Cholesterol - Proteins (apolipoproteins)

Fat Digestion

*Mouth --> Liver --> Pancreas --> Small Intestine --> Large Intestine* 1. Mouth (little or no fat is digested) - Lingual lipase 2. Stomach (little or no fat is digested) - Gastric lipase 3. Liver - Produces bile which is stored and released by the gallbladder into the common bile duct, which empties into the small intestine. - Bile emulsifies fat. 4. Pancreas - Pancreatic lipase --> digests triglycerides. - Phospholipase --> digests phospholipids. - Cholesterol esterase --> digests cholesterol. - Secretes these enzymes into the Common Bile Duct 5. Small Intestine - Fat is digested and absorbed into the duodenum. 6. Large Intestine - Less than 5% of fat passes through the Large Intestine and is excreted.

Phospholipids

- Amphipathic - Hydrophobic and hydrophilic ends - Components of cell membranes - Emulsifiers (e.g. bile) - Synthesized by the body - Foods: egg yolks, wheat germ and peanuts

Saturation

- Carbon atoms form 4 bonds with other atoms - Oxygen atoms form 2 bonds with other atom(s) - Hydrogen atoms form 1 bond with another atom

Sterol

- Carbons arranged in rings - Steroid hormones, bile, cell membranes - Synthesized by the body - Foods of animal origin (cholesterol) and plants sterols

Discuss the recommended intake of lipids.

- No RDA - AMDR: 20 - 35% of total calories Dietary Guidelines 2015: - Limit saturated and trans fat - AHA recommendations for those at risk for heart disease: - Limit saturated fats to 7% of total calories

Western Diet

- North American fat intake = high - Also total calories and sugar intake - Omega 6 FA intakes are plentiful - Beef, poultry, corn oil, etc. - Omega 3 FA intakes are usually low - Food sources: fish, canola oil, flaxseeds, walnuts, etc. - Supplements - Cautions for people with bleeding disorders

How does fatty acid structure affect shape?

- Unsaturated cis fatty acids have bent or kinked carbon chains - Saturated and unsaturated trans fatty acids have straight carbon chains - Chain length and shape determines whether fat is solid or liquid at room temp

Mediterranean Diet

- Up to 40% kcal from fat is healthy if mostly MUFA - Olive oil as main fat - Abundant fruits & vegetables, whole grains, beans, nuts, and seeds - Daily intake of small amounts of cheese and yogurt - Weekly fish intake; limited use of eggs and red meat - Regular exercise and rest - Moderate wine intake

The Dietary Guidelines for Americans recommend that total fat intake should not exceed __________ of total calories and saturated fat intake be limited to _______ or less of total calories.

35%, 10%

Lipids

9 kcal/g

Fatty Acids

A carboxylic acid consisting of a hydrocarbon chain and a terminal carboxyl group, especially any of those occurring as esters in fats and oils.

Explain the process of hydrogenation.

Addition of hydrogen atoms to a PUFA chain - Saturate carbon atoms - Makes bent PUFA straighter - Converts liquid oil to more solid fat

What is the role bile in digestion of lipids?

An emulsifier made in the liver from cholesterol. Bile contains bile acids, which are critical for digestion and absorption of fats and fat-soluble vitamins in the small intestine. Bile is released by the gallbladder into the small intestines where it emulsifies the fat in the chyme which allows the digestive enzymes to break down the triglycerides.

Discuss the health concerns related to dietary fat intake.

Atherosclerosis - A condition that causes the walls of the arteries to thicken. This constricts the flow of blood to the tissues, increasing the risk of heart attack or stroke. Cancer - Excessive consumption of dietary fats from dairy products and red meat increases the risk of pancreatic cancer. Obesity - Since your body can only store a limited amount of glycogen, the excess calories are converted to fat and stored as adipose tissue. Brain Injury - Eating foods high in saturated fats may damage your hypothalamus -- which is the area of your brain that regulates energy balance.

What are the differences between cis and trans fat?

Cis = hydrogen atoms are on same side of C=C *unsaturated* Trans = hydrogen atoms are on opposite side of C=C *saturated* The difference between cis and trans is that the two H atoms are on the same side of the double bond (cis), compared to being on opposite sides (trans). In a cis configuration, the double bond creates a kink in the fatty acid.

Fat Absorption

Fats are absorbed in the small intestine in the form of monoglycerides and free fatty acids. Short and medium chain - Fatty acids are absorbed in the portal vein Long chain - Fatty acids are re-esterified and enter lymphatic system. - Bile is recycled via enterohepatic circulation

Triglycerides

Glycerol + 3 fatty acids Provide energy: 9 kcal/g - TG = main fuel source for body cells (except nervous system and red blood cells); FA beta-oxidation - Provide compact energy storage - Excess calories from carbs, fat, protein, and alcohol are converted to FA's à esterification à TG for storage - Adipose cells: 80% lipid, 20% water/proteins - Insulate and protect the body - Subcutaneous fat (just beneath skin) helps keep body temperature at constant level - Visceral fat (packed around some organs) protect organs - Aid fat-soluble vitamin absorption and transport - Essential fatty acids --> eicosanoids

Which of the following is a risk factor for heart disease?

High total cholesterol

Describe the dietary measures to reduce the risk of developing cardiovascular disease.

Lower cholesterol levels. To help lower cholesterol levels, eat a diet low in cholesterol, saturated fat, and refined sugars and high in fiber.

Cholesterol is

Not essential in the diet; the human body can synthesize it. Not found in foods of plant origin. An important part of human cell membranes and is necessary to make some hormones.

Which of the following groups of foods would contribute a substantial amount of monounsaturated fatty acids to the diet?

Olive oil, peanuts, and almonds.

Polyunsaturated vs. Monounsaturated

Polyunsaturated and monounsaturated fat are both unsaturated fats. "Poly" means many unsaturated chemical bonds and "mono" means one unsaturated chemical bond. Both types of unsaturated fats may help lower your blood cholesterol level when used in place of saturated fat in your diet.

Saturated vs. Unsaturated Fatty Acids

Saturated = carbons saturated with hydrogen atoms Unsaturated = carbon double bond(s) Saturated fats are solid at room temperature, while unsaturated fats are liquid at room temperature. This is because saturated and unsaturated fats differ in their chemical structures. Saturated fats have no double bond between molecules, which means there are no gaps and the fat is saturated with hydrogen molecules.

How does the fatty acid chain length affect digestion/absorption?

Short chain and medium chain fatty acids can directly enter the lymphatic system while long chained fatty acids must be transported by a lipoprotein.

Why must essential fatty acids be provided by the diet? Give examples of essential fatty acids. What roles do essential fatty acids play in the body?

The body can synthesize most of the fats it needs from the diet. However, two essential fatty acids, *linoleic and alpha-linolenic*, cannot be synthesized in the body and must be obtained from food. These basic fats, found in plant foods, are used to build specialized fats called omega-3 and omega-6 fatty acids.

How does cholesterol leave circulation?

There are 3 pathways for cholesterol uptake by various cells: 1. HDL: Reverse cholesterol transport pathway 2. LDL: Receptor-mediated endocytosis (receptor pathway) 3. Ox-LDL: Scavenger pathway

Trans fatty acids

They raise LDL and lower HDL cholesterol.

What are the health risks of trans fatty acids?

Trans fats raise your bad (LDL) cholesterol levels and lower your good (HDL) cholesterol levels. Eating trans fats increases your risk of developing heart disease and stroke. It's also associated with a higher risk of developing type 2 diabetes.

What is the main structural difference between phospholipids and triglycerides and sterols?

Triglycerides (TG) - Hydrophobic (nonpolar) - 95% of dietary lipid - 95% of stored fat in body Phospholipids - Amphipathic (polar + nonpolar) parts Sterols - Hydrophobic but less than TG

What chemical characteristics do all lipids have?

Unlike carbohydrates and proteins, lipids are generally insoluble in water. Lipids refer to organic biochemicals such as fats, oils, sterols, phospholipids, lipoproteins and waxy elements. Lipids store energy, are structural components of cell membranes and also help in the synthesis of vitamins and hormones.

Saturated fatty acids predominate in which of the following lipids?

butter

Immediately after a meal, newly digested and absorbed dietary fats appear in the lymph, and then the blood, as a part of which of the following?

chylomicron

Trans fatty acids are now considered more atherogenic than saturated fatty acids because they

elevate LDL levels, while decreasing HDL.

High-density lipoproteins function in lipid transport by

picking up cholesterol from dying cells and other sources for delivery to other lipoproteins and the liver for disposal.

Lipids with high saturated fatty acid content are ____________ at room temperature.

solid