| Before we look at trans fats we will take a look at normal fats. Fats and oils, fats which are liquid at room temperature, are produced by plants and animals as an energy store. In animals fat also serves as an insulator. All fats and oils have a similar structure, three long chain fatty acids, between 12 to 20 carbons in length, attached to a glycerol molecule, as shown on the right. Fats and oils are referred to as triglycerides. Page 2Hydrogenation is a process used by food makers to convert a cis to a trans double bond. During hydrogenation a cis unsaturated fat is heated at high pressure and in the presence of hydrogen gas and a nickel catalyst yields a trans double bond. Until recently partially hydrogenated fatty acids were thought to be as healthy as the cis unsaturated fatty acids they were made from. But recently links to various serious health risks, that include cancer, have been suggested. One prevalent theory is that a fat digesting enzyme, known as lipase, is unable, to breakdown trans-fatty acids and hence these build up in the blood causing significant damage and blockage to blood vessels. Trans fats have a semisolid property much liked by consumers. Margarine was advertised as a healthy alternative to butter and more convenient to use because the partially hydrogenated fatty acids made margarine spread easily on bread.
It glistens with fat, from the cheese to the steak. You may never have visited Philadelphia, but you probably know about its famous gastronomic delight, the Philly cheesesteak, pictured here. Both cheese and steak are typically high-fat foods, so this sandwich is definitely not recommended if you are following a low-fat diet. We need some fats in our diet for good health, but too much of a good thing can be harmful to our health, no matter how good it tastes. What are fats? And why do we have such a love-hate relationship with them? Read on to find out. 
Fats are actually a type of lipid. Lipids are a major class of biochemical compounds that includes oils as well as fats. Organisms use lipids to store energy and for many other uses. Lipid molecules consist mainly of repeating units called fatty acids. There are two types of fatty acids: saturated fatty acids and unsaturated fatty acids. Both types consist mainly of simple chains of carbon atoms bonded to one another and to hydrogen atoms. The two types of fatty acids differ in how many hydrogen atoms they contain.
In saturated fatty acids, carbon atoms are bonded to as many hydrogen atoms as possible. All the carbon-to-carbon atoms share just single bonds between them. This causes the molecules to form straight chains, as shown in Figure \(\PageIndex{2}\). The straight chains can be packed together very tightly, allowing them to store energy in a compact form. Saturated fatty acids have relatively high melting points, explaining why they are solids at room temperature. Animals use saturated fatty acids to store energy.
In unsaturated fatty acids, some carbon atoms are not bonded to as many hydrogen atoms as possible. Instead, they form double or even triple bonds with other carbon atoms. This causes the chains to bend (see Figure \(\PageIndex{2}\)). The bent chains cannot be packed together very tightly. Unsaturated fatty acids have relatively low melting points, which explains why they are liquids at room temperature. Plants use unsaturated fatty acids to store energy. Monounsaturated fatty acids contain one less hydrogen atom than the same-length saturated fatty acid chain. Monounsaturated fatty acids are liquids at room temperature but start to solidify at refrigerator temperatures. Good food sources of monounsaturated fats include olive and peanut oils and avocados. Polyunsaturated fatty acids contain at least two fewer hydrogen atoms than the same-length saturated fatty acid chain. Polyunsaturated fatty acids are liquids at room temperature and remain in the liquid state in the refrigerator. Good food sources of polyunsaturated fats include safflower and soybean oils and many nuts and seeds.
Lipids may consist of fatty acids alone, or they may contain other molecules as well. For example, some lipids contain alcohol or phosphate groups. Types of lipids include triglycerides, phospholipids, and steroids. Each type has different functions in living things.
Triglycerides are formed by combining a molecule of glycerol with three fatty acid molecules. Glycerol (also called glycerine) is a simple compound known as a sugar alcohol. It is a colorless, odorless liquid that is sweet tasting and nontoxic. Triglycerides are the main constituent of body fat in humans and other animals. They are also found in fats derived from plants. There are many different types of triglycerides, with the main division being between those that contain saturated fatty acids and those that contain unsaturated fatty acids. In the human bloodstream, triglycerides play an important role in metabolism as energy sources and transporters of dietary fat. They contain more than twice as much energy as carbohydrates, the other major source of energy in the diet. When you eat, your body converts any calories it doesn't need to use right away into triglycerides, which are stored in your fat cells. When you need energy between meals, hormones trigger the release of some of these stored triglycerides back into the bloodstream.
Phospholipids are a major component of the cell membranes of all living things. Each phospholipid molecule has a "tail" consisting of two long fatty acids and a "head" consisting of a phosphate group and glycerol molecule (see diagram below). The phosphate group is a small negatively charged molecule. The phospholipid head is hydrophilic or attracted to water. The fatty acid tail of the phospholipid is hydrophobic or repelled by water. These properties allow phospholipids to form a two-layer, or bilayer, cell membrane. As shown in the diagram below, a phospholipid bilayer forms when many phospholipid molecules line up tail to tail, forming an inner and outer surface of hydrophilic heads. The hydrophilic heads point toward both the watery extracellular space and the watery intracellular space (lumen) of the cell.
Steroids are lipids with a ring structure. Each steroid has a core of seventeen carbon atoms arranged in four rings of five or six carbons each (see model pictured below). Steroids vary by the other components attached to this four-ring core. Hundreds of steroids are found in plants, animals, and fungi, but most steroids have one of just two principal biological functions: some steroids, such as cholesterol, are important components of cell membranes; many other steroids are hormones, which are messenger molecules. In humans, steroid hormones include cortisone, a fight-or-flight hormone; and the sex hormones estrogen and testosterone.
During a routine checkup with your family doctor, your blood was collected for a lipid profile. The results are back, and your triglyceride level is 180 mg/dL. Your doctor says this is a little high. A blood triglyceride level of 150 mg/dL or lower is considered normal. Higher levels of triglycerides in the blood have been linked to increased risk of atherosclerosis, heart disease, and stroke. If a blood test reveals that you have high triglycerides, the levels can be lowered through healthy lifestyle choices and/or prescription medications. Healthy lifestyle choices to control triglyceride levels include:
If healthy lifestyle changes aren't enough to bring down high triglyceride levels, drugs prescribed by your doctor are likely to help.
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Watch the video below to learn more about triglycerides and the difference between saturated and unsaturated fatty acids. |
What is a fatty acid with the maximum of hydrogen atoms possible?
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