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.

Do Fat Cells Do More Than Store Energy?

For a long time fat tissue and their cells were viewed as somewhat inert containers of energy storage. However, today we know that adipose tissue functions as a gland with the capability to release a variety of factors relative to its size and endowed energy. As mentioned previously, some of these factors may promote the formation of more fat cells. Perhaps some of the most interesting released factors are those that circulate to the brain and provide insight to our energy storage status. One of the most important factors seems to be the hormone leptin. Fat cells release more and more leptin into our circulation when fat cells accumulate more fat. Leptin then signals the brain to reduce appetite. In addition, as fat cells swell due to excessive calorie consumption, some of the chemicals they release can promote the development and worsening of diabetes, high blood pressure and other medical conditions.

Are We Born with All of the Fat Cells We Will Ever Have?

We are not born with a full complement of fat cells as some scientists once thought. The number of fat cells in the body increases at various stages throughout growth, but by the time adulthood is reached the total number of these cells can become fixed. This means that if our body fat mass does not change, we probably would not produce new fat cells as adults. However, if we consume excessive calories, the number of fat cells can increase. In adipose tissue there is a small number of so-called pre-adipocytes or fat stem cells. When these cells are signaled, they will produce new fat cells. As you may have guessed, the signals are chemicals, many of which are released by existing fat cells when they become swollen with an increased bounty of stored fat.

Are There Advantages to Storing Energy as Fat?

Storing excess energy as fat rather than as protein or carbohydrate has great advantages. First, we are able to store more than twice the amount of energy in 1 gram of fat (9 calories) as we can in 1 gram of carbohydrate or protein (4 calories). Second, stored fat will have a lot less water associated with it than would be stored in carbohydrate and protein. The net effect of storing excess diet energy as fat versus carbohydrate or protein is that our body weight and volume are minimized. Said differently, it allows the human body to be lighter and smaller despite significant energy stores.

Storing energy as fat, versus carbohydrate or protein, allows our body to remain smaller and lighter.