One of the most fundamental rules of biology is that cells need energy to sustain life. Einstein discovered that all matter contains energy, but the cells can only use specific types of organic nutrients. In the human body, these nutrients are carbohydrates, proteins and fats. A series of complex reactions convert the biochemical energy from the major nutrients into adenosine triphosphate, or ATP for short. ATP is sometimes known as an energy currency. It moves throughout the body and breaks down to release its energy and power various metabolic processes such as muscle contractions. Body fat is merely potential cellular energy waiting in storage for conversion into ATP.
Fat Storage
When you eat, your body converts any excess calories that it doesn't need immediately into the fat molecule known as a triglyceride. Specialized fat cells store triglycerides for later use. In between meals, hormones release triglycerides from storage as a source of energy. The human body has a complex regulatory system that releases triglycerides at the correct time -- for example, during periods of low blood sugar or increased stress.
Fat Conversion
Triglycerides are actually made of three fatty acid molecules chained together, and so the human body needs some sort of mechanism to convert other molecules into fats for storage. This is the process of lipogenesis --- literally meaning the genesis of lipids. The cells have the option to convert carbohydrates, proteins and fats into the molecule acetyl CoA, which acts as a central hub for the metabolism of energy. Acetyl CoA normally contributes to the synthesis of ATP. In the presence of excess energy, however, it can also convert into triglycerides through the process of lipogenesis.
Nutrients
Carbohydrates are the main source of energy in the human diet. They have three possible fates. The cells can immediately convert carbohydrates into energy; a single sugar can yield between 36 and 38 molecules of ATP. The cells can also convert them into glycogen, a type of carbohydrate, for long-term storage; however, the storage capacity of glycogen is extremely limited. The final option is the conversion into fats. Approximately 55 percent of the carbohydrates in your diet are involved in the synthesis of fats. In fact, the hormone insulin helps regulate both blood sugar and the process of lipogenesis simultaneously. At the other end of the spectrum, protein is the least likely to become triglycerides, because it's involved in so many other processes throughout the human body.
Body Fat and Health
In general, excess body fat is associated with poor long-term health such as insulin resistance and heart disease. Fat cells are biologically active sites and rely upon an extensive network of blood capillaries to connect with the rest of the body, which can put additional strain on your heart. High levels of triglycerides circulating in the blood are also associated with hardening of the arteries. The complex interplay among obesity, diabetes, cardiovascular disease and high levels of blood sugar and fats is something that researchers are still debating.
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