Does Fat Play a Structural Role in Our Body?

Our cell membranes contain molecules, called phospholipids, that seem to have structural similarities to triglycerides (see Figure 5.1). Like triglycerides, phospholipids contain a glycerol backbone to which fatty acids are attached. However, phospholipids contain only two fatty acids, not three as in triglycerides. The third fatty acid is replaced by phosphate combined with another molecule, such as choline, serine or inostiol. This helps make the phospholipids special and appropriate to be part of the

membrane.

Phospholipids provide the basis for the water-insoluble properties of our cell membranes. In turn, then, the barrier-like properties of membranes allow each cell to regulate the movement of water-soluble substances into and out of cells and their internal organelles. In addition, the attached fatty acids can be removed and used to make other molecules that help regulate bodily function.

What Is Brown Adipose Tissue?

While most of the fat tissue in an adult’s body is somewhat pale (white adipose tissue), infants tend to have a fair amount of brown adipose tissue (BAT). This type of fat tissue is a little different from white adipose tissue as it contains a lot more blood vessels. This is one reason why it appears darker in color. BAT is especially important for infants to help them maintain their body temperature. When infants are born, they are fairly lean and it is easy for heat to leave their bodies. BAT has the ability to increase some of its metabolic events, which results in the generation of extra heat. BAT is able to uncouple the process of ATP formation via the breakdown of energy nutrients. Although this may seem somewhat “futile” when it comes to making ATP, the molecule that cells use to power most operations, it does allow for the generation of heat which will help maintain the body temperature of the baby. For adults, this may seem like a great way of burning unwanted fat, but this isn’t to be, because as babies become children and then teens, the amount of BAT is reduced and becomes almost nonexistent by adulthood.

Does Body Fat Help Our Body Conserve Body Heat?

Subcutaneous fat not only helps protect skeletal muscle from trauma but it also helps conserve our body heat. This is because fat tissue is a relatively good insulating tissue. Maintaining our body temperature allows cell operations to function optimally. Interestingly, too little subcutaneous body fat might allow for greater heat losses daily. This might partly explain why a leaner person may have a higher energy expenditure than another person having the same body weight but who is less lean. Following this line of thinking it would be easier for a leaner person to maintain their body weight than a heavier person. We’ll take a closer look at this in Chapter 7.

Body fat is important to maintain body temperature and to protect organs and muscle.

Can Fat Help Protect the Body?

Fat tissue provides some protection to various tissues in the body. For instance, fat tissue around our internal organs provides some cushioning. This helps protect the organs against external trauma. Furthermore, the subcutaneous layer of fat storage also provides some cushioning, which protects muscle. Subcutaneous fat is not well vasculated, meaning that there aren’t a lot of blood vessels in that tissue relative to other tissue. Meanwhile, skeletal muscle is heavily endowed with blood vessels which provide oxygen and energy nutrients during activity and exercise. In the absence of subcutaneous fat it would be easier to rupture smaller blood vessels in skeletal muscle, which then would be evident in bruises. As an example, prior to competition, bodybuilders will be very cautious not to bang into things or play contact sports (rugby, football, roller hockey, etc.). As they attempt to “lean out” for the competition, they reduce their subcutaneous fat to nadir levels, which would allow them to bruise more easily. This then would impact their aesthetic presentation during the bodybuilding competition.

Can Carbohydrate from Our Diet Become Body Fat?

Since the potential to store carbohydrate as glycogen is somewhat limited, we need another means of storing excessive diet carbohydrate energy. As our liver and skeletal muscle is busy making glycogen, our liver and fat tissue will also begin to convert some of the extra glucose to fat. The fat that is made in our fat cells is stored within those cells. Meanwhile, the fat that is made in the liver is transported in the blood to fat cells and to a lesser degree other tissue such as muscle, breast tissue, etc.

Excessive carbohydrate intake can be converted to fat and decrease daily fat use leading to increased body fat.

Interestingly, scientists have determined that our ability to convert excessive carbohydrate to fat might not be as efficient under normal conditions as we once thought. It now seems that consuming excessive carbohydrate can increase the level of body fat by decreasing our use of fat as a daily energy source. That’s because our body is forced to use more carbohydrate as promoted by insulin. This situation tends to happen more when people eat too many calories and have type 2 diabetes (or prediabetes).

How Much Glycogen Is in Our Body?

Our liver can store up to 6 to 8 percent of its weight as glycogen for about 75 to 100 grams total. Meanwhile, only about 1 percent of the weight of skeletal muscle cells is attributable to glycogen. However, since the total amount of skeletal muscle in our body far exceeds our liver, muscle will contribute much more to our total glycogen stores. Skeletal muscle can contain about 250 to 400 grams, which is about four-fifths of our total glycogen stores. Since carbohydrate provides 4 calories per gram the potential energy from glycogen is typically 1,400 to 2,000 calories, not very much. As you may expect, people with more muscle resulting from exercise training will have more body glycogen owing to increased muscle mass. In addition, their muscle will adapt to double and even triple the amount of glycogen it can store.
 

Interestingly, even though carbohydrates contribute approximately one-half of the energy in our diet, our body composition is not reflective. That’s because only 1 percent or less of our body weight is composed of carbohydrate. This means that carbohydrate is stored with limitations, most of which is in our liver and skeletal muscle as glycogen. Other tissues, such as fat cells and the heart, contain a little glycogen as well; however, the contribution to our total body glycogen stores is very small. Since glycogen stores are relatively small there must be another means of storing the excessive energy from diet derived carbohydrate.

What Does Our Body Do with the Glucose from a Meal?

Insulin directs muscle, fat tissue, and the liver to use glucose, fructose and galactose as the primary fuel. This allows for a lot of carbohydrate entering the body from a meal to be used for energy immediately. In

addition, insulin directs muscle and liver, and to a lesser extent other tissue, to store extra carbohydrate as glycogen. Glycogen is composed of large branching links of glucose and is very similar to plant starch. However, only so much glycogen can be made and stored, since it is meant to be a short-term not a long-term energy reserve.

How Does Our Body Respond to the Rise in Blood Glucose?

The concentration of glucose in the blood is very tightly regulated. When the level of circulating glucose climbs above the normal fasting level, the pancreas releases the hormone insulin (see Figures 4.2 and 4.3). Insulin will interact with receptors on muscle cells and fat cells and promote the movement of glucose into these cells. Because skeletal muscle and fat cells together tend to make up more than half of our total body mass, the net effect is a fairly rapid lowering of the glucose concentration. Insulin increases the movement of glucose in these cells by increasing the number of glucose transport proteins on their plasma membranes. As the level of glucose returns to the normal fasting level, the pancreas responds by releasing less insulin into circulation.
 

All cells in our body will continuously take glucose from our blood throughout the day to help meet their need for energy. However, after a meal, the liver, muscle, and fat cells will take a lot more glucose out of the blood than they immediately need. This allows blood glucose levels to quickly return to a normal fasting concentration.
 

Increased blood glucose levels causes the release of insulin to process, use, and store carbohydrate.

What Do Carbohydrates Do in Our Body?

Carbohydrates play quite a few roles in the human body, but perhaps none as important as being an energy source for all cells. All cells in the body will use glucose to some degree. Meanwhile, cells of the central nervous system as well as red blood cells and certain other types of cells will exclusively use glucose under normal situations. Carbohydrates also provide a limited yet readily available energy store called glycogen. As an energy source, carbohydrate provides 4 calories per gram.
 

Carbohydrates are also a modest yet vital component of cell membranes. Certain carbohydrates are also key portions of indispensable molecules. For example, molecules such as DNA and RNA contain the carbohydrate ribose. Ribose is a monosaccharide that can be made in our cells from glucose. Very complex carbohydrates called glycosaminoglycans (GAGs) are important in connective tissue, such as in our joints. The GAGs include chondroitin sulfate and hyaluronic acid, which are popular nutrition supplements for joint inflammatory disorders. We’ll spend more time discussing arthritis and nutrition in Chapter 12.
 

Carbohydrate serves as energy for all cells in our body and is used tomake structural molecules, such as those found in joints.

Carbohydrates Power Our Body

The term carbohydrate was coined long ago as scientists observed a consistent pattern in the chemical formula of most carbohydrates. Not only were they composed of only carbon, hydrogen, and oxygen but also the ratio of carbon to the chemical formula of water (H2O) is typically 1 to 1 (C:H2O). Carbohydrate means “carbon with water.” For example, carbohydrates glucose and galactose have the following chemical
formula:

How Does the Heart Supply Blood Throughout Our Body?

As our heart contracts, blood is pumped from the left ventricle into the aorta. Blood moves from the aorta into the arteries, then arterioles, and finally tiny capillaries in our tissue. The blood leaving our left ventricle is rich with oxygen while the blood returning to our heart from tissue throughout our body has given up oxygen to working cells while acquiring carbon dioxide. This blood is then pumped by the right ventricle to the lungs to reload the hemoglobin with oxygen and release carbon dioxide.

How Do We Bring Oxygen into Our Body and Get Rid of Carbon Dioxide?

When the heart pumps, blood is propelled from the right ventricle into the pulmonary arteries for transport to the lungs. Pulmonary means lungs. Upon reaching the lungs and the pulmonary capillaries, carbon dioxide exits the blood and enters into the airways of our lungs. It is then removed from our body when we exhale. At the same time, oxygen enters the blood from the airways of our lungs and binds with hemoglobin in RBCs. The oxygen-containing blood leaves the lungs and travels back to the heart as part of circulation. Thus every breath you take serves to exchange gases, bringing needed oxygen into your body while removing carbon dioxide.

Do Individual Cells and Our Body as a Whole Attempt to Maintain an Optimal Working Environment?

Just as you clean your apartment or house and determine what kind of stuff is found within your living area, so too will our cells clean and regulate the contents in their intracellular fluid. This allows each cell to maintain an optimal operating environment. Scientists often use the term homeostasis to describe the efforts associated with the maintenance of this optimal environment. Furthermore, just as it is the responsibility of each cell to maintain its own ideal internal environment; at the same time many of our organs work in concert to regulate the environment within our body as a whole. These organs include the kidneys, lungs, skin, and liver. Many of our most basic functions, such as breathing, sweating, urinating, digesting, and the pumping of our heart, are actually functions dedicated to homeostasis (Table 2.2). Therefore, homeostasis is the housekeeping efforts of all our cells working individually as well as together to provide an environment conducive to optimal
function.

What Is the Most Basic Composition of Our Body?

Let’s say that we had access to fancy laboratory equipment capable of determining the most fundamental composition of an object. If we used this equipment to assess a man or woman it would spit out some interesting data on our most basic level of composition—elements. Elements are substances that cannot be broken down into other substances. Scientists have determined that there are one hundred or so of these elements in nature. Some of the more recognizable elements include carbon, oxygen, hydrogen, nitrogen, iron, zinc, copper, potassium, and calcium. All of the elements known to exist can be found on the periodic table of elements, which we have all come across at one point or another in our schooling. (the periodic table of elements is included as Appendix A in case you feel the need for another peek.) Now, imagine that everything that you can think of is merely a skillful combination of these same elements. This includes cars, boats, buildings, clouds, oceans, trees, and of course our body. In fact, our body employs about twenty-seven of the elements as displayed in Table 1.1 and Appendix A.

What Is the Element Composition of Our Body?

The late, great Carl Sagan in his personal exploration of the cosmos said that we are made up of “star stuff.” What he meant was that our body is made up of many of the very same elements that make up planets and
other celestial bodies in the universe. We humans, as well as other lifeforms on our planet, have simply borrowed these elements. Interestingly, four of these elements, namely oxygen, carbon, hydrogen, and nitrogen, make up greater than 90 percent of our body weight. Since the majority of these elements are found in our body as part of substances such as water, proteins, carbohydrates, fats, and nucleic acids (DNA and RNA), it only makes sense that these substances must be the major chemicals of

our body. For example, a lean, young adult male’s body weight may be approximately 62 percent water, 16 percent protein, 16 percent fat, and less than 1 percent carbohydrate. Most of his remaining weight (about 5 percent) would be attributed to minerals. We will spend a lot more time talking about the finer details of body composition in later chapters.
 

Our body is mostly made of water, fats, protein, carbohydrate, minerals, DNA, and other special molecules.