Chapter 5. Lipids
Chapter Review
IMPORTANT: Key Takeaways
- Triglycerides, phospholipids, and sterols comprise the lipid family.
- The main form of lipids found in the body, triglycerides are composed of glycerol and fatty acid chains. The fatty acids fall under two categories: saturated (containing all single carbon bonds) and unsaturated (containing one or more double carbon bonds). Saturated fatty acids tend to be straighter and solid at room temperature, and unsaturated fatty acids have kinks and tend to be liquid at room temperature.
- Phospholipids are diglycerides that are composed of a glycerol backbone that has two fatty acid molecules and a phosphate group attached to it. Phospholipids are amphiphilic- the fatty acid sides are hydrophobic and the phosphate group is hydrophilic. Phospholipids form a double layer in cell membranes, which protects the inside of the cell from the external environment while regulating the transport of fats and water in and out of the membrane.
- Sterols are complex molecules containing interlinking rings of carbon atoms, with side chains of carbon, hydrogen, and oxygen attached. Cholesterol, the most well-known sterol, is used in the body to make vitamin D, glucocorticoids, and sex hormones. Additionally, cholesterol is the primary component of bile. Excess accumulation of cholesterol in the blood, however, poses a threat to our health. When dietary consumption of cholesterol is high, the body downregulates its production to maintain healthy levels.
- Unlike carbohydrates that are stored as glycogen with heavy water content, lipids are energy-dense compounds that are stored dry and with greater amounts of energy in a reduced space (they provide 9 kcal/g). Lipids are particularly used to fuel low-intensity exercise or used during rest. However, as the body’s glycogen stores begin to deplete, we experience a greater reliance on fats for energy.
- Lipid digestion begins in the mouth with chewing and enzymes found in saliva (ie. lingual lipase). In the stomach, gastric lipase breaks down triglycerides into diglycerides and fatty acids, and the stomach’s churning and contractions further disperse the fat molecules. In the small intestine, bile emulsifies fats, making them accessible to digestive enzymes (ie. pancreatic lipase) which break down fats into free fatty acids and monoglycerides.
- Bile salts envelop the fatty acids and monoglycerides to form micelles, allowing for the transportation of fats to the intestinal microvillus. Chylomicrons, which are large lipoproteins, transport food fats through the lymphatic system and bloodstream to be used as energy by our muscles, used to make lipid-containing compounds or stored in the muscle/adipose tissue for later use.
- In relation to our total caloric intake, trans fat consumption should be less than 1 percent, saturated fat consumption should be less than 10 percent, and the majority of fats consumed should be polyunsaturated and monounsaturated fats. The AI for omega-6 fatty acids is 11-12 g/day for women and 14-17 g/day for men, which translates to an AMDR of 5-10% of energy intake. The AI for omega-3 fatty acids is 1.1 g/day for women and 1.6 g/day for men, which translates to an AMDR of 0.5-1.2% of energy intake.
- A build-up of blood cholesterol can lead to a blockage in blood vessels and restriction of blood flow. Healthy total blood cholesterol levels should be maintained below 200 mg/dL. LDL is known as “bad cholesterol” and HDL is known as “good cholesterol.” Polyunsaturated fatty acids lower LDL levels and elevate HDL levels, while trans fatty acids increase LDL levels and decrease HDL levels. Trans fats are associated with an elevated risk of coronary heart disease and mortality, tissue inflammation throughout the body, insulin resistance, weight gain, and digestive troubles.
- Improper dietary fat consumption can result in an increased level of lipids, triglycerides, and cholesterol in the blood called hyperlipidemia, which may result in adverse health problems such as cardiovascular disease, heart attack, ischemic stroke, congestive heart failure, arrhythmia, heart valve problems, and obesity.
Practice Questions
- What are the three types of lipids and what roles do each play in the body?
- How does the degree of fatty acid saturation typically affect the state of fats at room temperature?
- What is hydrogenation? How does this process alter the properties of fats?
- Considering what you have learned about the health implications of eating saturated and unsaturated fats, what dietary adjustments can you make to eat healthier?
- What is the difference between essential and non-essential fatty acids and why is this distinction important to consider when planning your diet?
- What is the difference between the health benefits of eicosanoids derived from omega-3 fatty acids and eicosanoids omega-6 fatty acids?
- What is unique about the structure of phospholipids?
- What is the role of food emulsifiers? Provide some examples of food emulsifiers.
- Why is it important for individuals to maintain healthy blood cholesterol levels?
- How do dietary choices influence cholesterol absorption?
- How do fats move in a water-based environment despite their water-insoluble nature?
- What are the potential health implications of fat malabsorption?
- How does the body store and use triglycerides from food for energy production?
- What are the functions of lipids in the body? Briefly explain each function.
- According to existing health guidelines, ideally, which types of fats should be consumed in higher amounts, and which should be limited?
- What are the major lipoproteins and what are their functions?
- List and explain the potential adverse health consequences of high blood lipid levels.
