“Chapter 3: Lipids” Mmmmm…fat. The good, the bad, and the artery-clogging
Do You Ever… • Think of fats as unhealthy foods that are best eliminated from the diet? • Wonder about the differences between “good” and “bad” cholesterol? • Choose fish for health’s sake without fully knowing why? • Recognize invisible fats in your foods?
Let’s say… • Your bill from a lab reads “Blood lipid profile: $250.” • Your doctor tells you that your blood cholesterol is high. • The doc also tells you to cut down on saturated fats. • But what does it all mean?
Intro to the Lipids • “The lipids in foods and in the human body fall into three classes.” • Each of these are stored in different parts of the body, and found in different foods.
“About 95% are triglycerides.” • “The rest are phospholipids and sterols.” • (Cholesterol is the best known) • Some of these names may sound familiar…we’ll discuss them in more detail later.
What are fat’s uses in the body? • “Fat is the body’s chief storage for the energy from food eaten in excess of need.” • Evolutionarily, if you didn’t know where your next meal was coming from, it made sense to store extra.
“Most cells store limited fat.” • “Fat cells are specialized and can expand almost indefinitely.” • So the more fat they store, the larger they grow.
These aren’t just sacks of fat, though! • “Adipose (fat) tissue secretes hormones that regulate appetite and influence other body functions.” • So these cells are, indeed, important to our health.
Why not just store energy in carbs? • Glycogen (sugar storage) holds a great deal of water, so it is a bulky, heavy molecule. • Fats pack tightly together, and store more energy in a small space.
What else does fat do? • “Pads of fat surround and protect our vital organs.” • This is why we are very durable and aren’t injured easily.
“Fat under the skin insulates us.” • This protects us from both hot and cold, like a thermos. • “It is also part of our cell membranes.”
“Fat is needed to absorb vitamins A, D, E, and K, which are fat-soluble.” • This means that they only dissolve into fat. • “Our bodies make molecules from essential fatty acids (part of fat).” • So our fat is absolutely vital!
Usefulness of Fats in Food • The energy density of fat makes it valuable in some situations. • A hunter or hiker can carry fat calories easier than carb calories, because fat is lighter.
Fat is naturally appealing to us, because evolutionarily, we needed calories! • Fat also adds tenderness to meats and baked goods. • “Fat contributes to satiety, feeling full after a meal.” • The fat triggers a physiological response that slows digestion and stops us from eating more.
Although fat in the stomach signals us to stop eating, • The taste of fat tells us to keep eating, so it is possible to overeat easily.
A Closer Look At Fat • “Fat usually refers to triglycerides.” • “Made of three fatty acids and one glycerol molecule.”
Tissues all over the body can assemble or disassemble these triglycerides as needed. • “Fatty acids differ in two ways:” • “Chain length”
“and degree of saturation.” • Saturated, unsaturated…more about that in a minute. • Usually, triglycerides contain a mixture of different fatty acids.
“The shorter the chain, the softer and more liquid the fat.” • So vegetable oils have shorter molecule chains; • Beef fat has a longer chain of fatty acids. • This does matter!
“Each species of animal makes different triglycerides.” • This is governed by genetics. • Fats in the diet can affect which triglycerides are made, because the fatty acids we eat are often incorporated into our triglycerides in the body. • Remember, you are what you eat!
Saturated vs. Unsaturated Fatty Acids • Saturation: whether or not a fatty acid chain is holding all of the hydrogen atoms it can hold.
“If every available bond is holding a hydrogen molecule, that chain is a saturated fatty acid.”
Sometimes, in the fats of plants and fish, this chain has a place where hydrogens are missing. • “A chain with one missing hydrogen is monounsaturated.”
“A fat with two or more missing hydrogens is polyunsaturated.” • All of this affects the point at which that fat melts.
“The more unsaturated, the more liquid it is at room temperature.” • So since beef fat is solid, it has lots of saturated fat. • Since chicken fat is softer, it has less saturated fat. • A good way to tell if it is healthy!
The Catch • Some liquid plant oils are still high in saturated fat. (coconut, palm) • How do we tell? • “Refrigerate oil: if it turns cloudy, it has more saturated fat.” • One exception is olive oil: although only mono-, good for you!
Where the Fatty Acids are Found • “fish, veggies: polyunsaturated” • “some veggies (canola, olive): monounsaturated” • “meat: most saturated” • Beware: veggie fat can contain trans fat…dangerous! (More later)
What’s so great about olive oil? • Rich in antioxidant phytochemicals • Excellent replacement for butter and other animal fats
“Phospholipids (PPLs) and Sterols” • “PPLs have two fatty acid chains instead of three, and a phosphorus molecule.” • Why does this matter? • “It is water- and also fat-soluble.” • So it dissolves in both water and fat. Why do we care?....
“Manufacturers use PPLs as an emulsifier to blend fats and water.” • One of the most common on labels: lecithin • Used in mayo to blend vinegar and eggs
“Sterols are rings of carbon atoms with hydrogens and oxygens attached.” • Cholesterol is the best known. • Good cholesterol is vital to cell membrane structure; bad cholesterol clogs arteries.
What is the difference? • “Low-density lipoproteins (LDL) are carriers of cholesterol to the tissues.” • These are larger, lighter, and richer in cholesterol.
“High-density lipoproteins (HDL) carry cholesterol away from tissues, to the liver for disposal.” • These are lighter, smaller, and contain more protein. • So both contain the same cholesterol…what’s with the good and bad?
We’ve come to call them good and bad cholesterols, when cholesterol is cholesterol. • The key is, “LDL carries lipids that trigger inflammation and contribute to heart disease.” • “HDL proteins oppose inflammation and protect against heart attack.”
Therefore, elevated LDL in the blood warns of an increased heart attack risk; • Elevated HDL points to a reduced risk. • These numbers are SO important to health! • So how do we change our numbers?
“LDL can be lowered by avoiding saturated fat and trans fat.” • Happily, the national cholesterol level is dropping! • But heart disease is still this country’s top killer. • “We should choose a diet with less than 10% of calories from saturated fat.”
How do we raise HDL? • “Diet rarely raises HDL; regular exercise works better.” • Although some foods, like olive oil, fiber, fish, and nuts can help. • Remember HDL = Happy DL
Coming soon… • More about fat!