“Saturated Fat & Cholesterol Lies” from “Fat Head” (Video)
Harvard School of Public Health – Fats and Cholesterol
How Does Your Body Use Fat and Cholesterol?
Some people, like Diane, whom you read about in the beginning of the chapter, try to avoid fat in their diets, as they think it is unhealthy. This can actually be counterproductive, because fat plays many key roles in your body. Fat is an important source of energy and helps the absorption of some compounds. Fat also insulates your body and cushions your major organs. Some fats are essential for your good health. There are differences among the types of fat that you eat. Different fats can have different effects on your health, specifically your heart. Let’s look at the roles that fats play in your body.
Fat Is Used as Energy
At 9 calories per gram, compared with 4 calories per gram for both carbohydrates and protein, fat is a major fuel source for your body. Your body has an unlimited ability to store excess energy (calories) as fat. In fact, your fat reserves have the capacity to enlarge as much as 1,000 times their original size, as more fat is added. If your cells fill to capacity, your body can add more fat cells.
Your body only has a limited ability to store glucose, which is needed for the brain and red blood cells to function. When your blood glucose level begins to decline, the hormone glucagon promotes the release of glucose from the liver in order to supply the blood with glucose. Glucagon simultaneously promotes the release of fat from fat cells to provide additional energy for your body. Your heart, liver, and resting muscles prefer fat as their fuel source, which spares glucose to be used for your nervous system and red blood cells. In fact, fat is your main source of energy throughout the day. This fat stored in your fat cells provides a backup source of energy between meals. In a famine situation, some individuals could last months without eating, depending upon the extent of their fat stores and the availability of adequate fluids.
Fat Helps You Absorb Certain Compounds and Insulates the Body
Fat allows you to absorb the fat-soluble vitamins A,D, E, and K, as well as carotenoids, compounds that can have antioxidant properties in your body.1 Consuming inadequate amounts of fat may impede your absorption of these fat-soluble vitamins and compounds. The fat that is located just under your skin helps to insulate your body and maintain your body temperature. Fat also acts as a protective cushion for your bones, organs, and nerves.
Essential Fatty Acids Help Keep Cells Healthy
Two polyunsaturated fatty acids, linoleic acid and alpha-linolenic acid are essential, which means that your body can’t make them; thus, you need to obtain them from your diet. Linoleic acid is also referred to as an omega-6 fatty acid, and alpha-linolenic acid is commonly called an omega-3 fatty acid. If this sounds like Greek to you, it should. The letters of the Greek alphabet help identify the placement of the carbons in fatty acids. Omega is the last letter of the Greek alphabet. Because the numbering of the carbons in a fatty acid starts from the acid end and is counted outward, the omega carbon is the last carbon of the fatty acid. In alpha-linolenic acid, the first double bond occurs at the third carbon from the omega end. Hence, it is referred to as an omega-3 fatty acid.
The essential fatty acids help maintain healthy skin cells, nerves, and cell membranes. For example, a deficiency of linoleic acid can interfere with normal growth and result in inflammation of the skin. A deficiency in alpha-linolenic acid can affect the functioning of the brain and nervous system. Essential fatty acids are also necessary to make other substances your body needs. Linoleic acid is used to make another polyunsaturated fatty acid, called arachidonic acid. This fatty acid is important for your cells and for making eicosanoids, which are hormone-like substances. Among other roles, eicosanoids help with blood pressure, inflammation, and blood clotting.
Roles of Lipoproteins
The VLDL, LDL, and HDL lipoproteins transport fat and cholesterol to and from your liver.
- VLDLs deliver fatty acid made in the liver to the cells.
- LDLs transport cholesterol to the cells, in some cases into the arterial lining.
- HDLs transport cholesterol from the body cells and deliver it to the liver for disposal.
Fatty fish, such as salmon, are an excellent source of omega-3 fatty acids.
A limited amount of alpha-linolenic acid can be converted to two other important omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA and DHA have been shown to reduce the risk of heart disease, stroke, and diabetes.2 All fish contain EPA and DHA, although fatty fish such as salmon, herring, and sardines are especially rich sources. Cod-liver oil is abundant in EPA and DHA, but also in the fat-soluble vitamins A and D, which can both be toxic if consumed in high amounts. Eating fish is a safer way to obtain EPA and DHA, and it can also be very healthy for your heart.
Omega-6, linoleic acid, and omega-3, alpha-linolenic acid,must be consumed in a proper ratio. Some research suggests that a diet that has too much omega-6 fatty acids in comparison with omega-3 fatty acids may be unhealthy. Too much linoleic acid in relationship to alpha-linolenic acid can inhibit the conversion of alpha-linolenic acid to DHA, while the inverse (too much alpha-linolenic acid and not enough linoleic acid) can inhibit the conversion of linoleic acid to arachidonic acid.
Cholesterol Has Many Important Roles
Your body needs cholesterol both as a part of your cell membranes and as the precursor for vitamin D and bile acids. Cholesterol is also the precursor for the sex hormones such as estrogen and testosterone, which help to determine sexual characteristics. The confusion over cholesterol persists. Though dietary cholesterol has been proclaimed as unhealthy, the cholesterol in your blood can be either “good” or “bad” cholesterol. How can one substance be both Dr. Jekyll and Mr. Hyde? Later, we will look at the health effects of cholesterol, and try to clear up this confusion. During the discussion, keep in mind that the cholesterol in your diet isn’t the only factor that determines the levels of cholesterol in your blood.
Message
Fat contains 9 calories per gram and is an energy-dense source of fuel for your body. Fat cushions and protects your bones, organs, and nerves and insulates you to help maintain your body temperature. Fat also provides essential fatty acids and is needed for the absorption of fat-soluble vitamins and carotenoids. The essential fatty acids, linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid), are necessary to keep cells healthy. Linoleic acid is necessary to make arachidonic acid and eicosanoids. A limited amount of alpha-linolenic acid can be converted to two other omega-3 fatty acids, EPA and DHA, which are also found in fish. Cholesterol is part of your cell membranes and is needed to make vitamin D, bile acids, and sex hormones.
Essential Fatty Acids
Both linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid) are essential fatty acids that you have to obtain from your diet. Other fatty acids can be made from these fatty acids.
A deficiency of linoleic acid can interfere with normal growth and result in inflammation of the skin. Scaly skin can be a sign of inadequate amounts of alphalinolenic acid.
Terms:
Eicosanoids – Hormone-like substances in the body. Prostaglandins, thromboxanes, and leukotrienes are all eicosanoids.
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) – Two omega-3 fatty acids that are heart healthy. Fatty fish such as salmon are good sources
