Energy is the capacity to produce work, heath, light. Energy cannot be created or destroyed, it can only be transformed from one form to another. The whole life is a never-ending process of energy production. Death terminates this process. Energy on Earth comes from the Sun, thus it is called solar energy. Plants are capable to transform solar energy in chemical energy, through a process known as photosynthesis. This chemical energy is employed to produce substances as proteins, carbohydrates, fats, each of which produces energy.
Plants use solar radiations to synthesize carbohydrates from CO2 and water; the metabolism of carbohydrates in plants or in animal that eat them, releases energy and produces water and CO2 again.
Animals and humans cannot utilize directly the solar energy, but they can utilize that contained in plants or other animals. They oxidize carbohydrates, proteins, fats, alcohol to produce energy, carbon-oxide and water. The energy is vital for the body functions (for breathing, to make the hearth beating, to mantain body temperature, to move, to grow up and for tissues repairing). When energy is utilized, a part of it is always dissipated as heath. The more an organism is vital and strong, the more energy it owns and the more it can produce.
Inside cells the energy is produced into mitochondria, which utilize oxygen, fats, carbohydrates to produce ATP, the cells fuel. After its synthesis, ATP is transferred into cytoplasm by ATPases where it is utilized. The amount of ATP in one cell is sufficient to sustain the cell functions for one or two minutes, so the ATP is continuously hydrolyzed and regenerated. ATP reserves vary from one type of cell to another, for example, nervous cells have only few seconds of energy. From a glucose molecule, aerobically, 38 molecules of ATP are generated, while from a fat molecule (palmitic acid) 129 are produced. Anaerobically, from a glucose molecule only 2 ATP are generated, so the oxygen presence improves by 19 times the ATP production, that is energy.
ATP production is controlled and coordinated and regulates itself to work at the necessary speed to respond to the energetic needing of the cell.
Mitochondria are corpuscles contained in cytoplasm of the cells, having different sizes, from 0.2 to 2 micron. They are extremely dynamics, their shape continually varies; they are subjected to the osmotic pressure and pH. An excess of sodium damages them and the same do calcium surplus and free radicals. They are protected by anti oxidants, potassium and magnesium.
Energy is measured in calories. One calorie is the amount of energy necessary to increase the temperature of 1g of water, from 14.5 to 15.5 °C. The average introduction of calories is 2450 for men and 1680 for women.
The energy, in the diet is provided by proteins, fats, carbohydrates. 1 g of fats produces 9 calories, 1g of proteins produces 4 calories, and 1g of carbohydrates only 3.75.
The energy in foods depends on the amount of those three substances. The average needing of energy in people depends on the base metabolism and on the activity performed. The base metabolism is the amount of energy required by a person to perform, at rest, the base function of the body: an adult utilizes every minute 1.1 calories.
Base metabolism is measured in a person totally rested, and it varies from subject to subject. Children have a higher metabolism and men have a higher metabolism than women.
Nowadays we think that 2/3 of the total base metabolism are utilized by sodium and calcium pumps, to expel those substances out of the cells against gradient. The amount of energy needed by a person depends on her weight and activity.Energy used by a man of 25, with a weight of 65 kg during various activity.
- Sitting = cal /min 1,4
- Standing up = cal / min 1,7
- Washing / dressing = cal / min 3,5
- Walking, slowly = cal / min 3
- Walking, rapidly = cal / min 5
- Climbing stairs = cal / min 9
- Running = cal / min 21
- Swimming crawl, rapidly = cal / min 12
- Riding horse = cal / min 7
Energetic equilibrium:
In all living beings, energy is introduced and consumed. When diet provides more calories that that utilized by the body they are stored in fats.
