According to the Free Dictionary, Energy is the power which may be used for motion, overcoming resistance, or effecting physical changes; the ability to do work. However, this general statement on the definition of energy, in the many different fields of science energy may have a variety of definitions and uses. In Human Biochemistry, energy may be provided by lipids, proteins, and carbohydrates. Carbohydrates are the main source of partially oxidized energy, protein being a secondary source for energy. However, carbohydrates do not provide as much energy weight for weight as fats, which are used to store energy for a later use. Food is not the only source of energy, because the sun is always the first instance of energy for most organisms. Photosynthetic organisms capture energy from sunlight and convert it into carbohydrates, which are then broken down to energy using a process called cellular respiration (Cambridge). Cellular respiration produces energy-rich molecules, such as adenosine triphosphate, or ATP, to drive biochemical reactions.
The amount of energy required per individual is determined by the amount of physical activity they perform daily. The average man requires about 10,676 kilojoules (kJ), or about 2,550 kilocalories (kcal) per day, while average woman needs approximately 8,122 kJ (1,940 kcal) per day (Weight Loss Resource). The energy value of food is calculated through food calorimetry. A food (or bomb) calorimeter measures the heat of combustion. This is when a known mass of a particular food is ignited and completely burnt in the presence of oxygen; the energy released is transferred to water and the rise in temperature of the water is measured (Neuss). The energy in food can also be calculated using the following equation: q = mcT, where: q = heat evolved (J), m = mass of water (g), c = speci¬fic heat capacity of water (4.18 J/g °C)
Lipids are organic molecules with long hydrocarbon chains that are soluble in a non-polar solution (Neuss). Some of the functions of lipids are: energy storage, insulate and protect vital organs, and form cell membranes. There are the three types of important lipids: triglycerides (fats and oils), phospholipids (lecithin) and steroids (cholesterol).
Cholesterol is made in the liver, and is found throughout the blood, brain, spinal cord, and body tissue. Steroids are hydrophobic (nonpolar) molecules, which consist of a steroid backbone. Steroid backbones are made of three six-membered rings and a five membered ring fused together (Cambridge). Low-Density Lipids transport cholesterol to the arteries, where they clog the arteries, which can lead to cardiovascular diseases. High- Density Lipoproteins remove the cholesterol from the arteries and transport it back to the liver.
Fats and Oils