To get everybody up to speed I thought I would do an introduction to the biology behind human metabolism.
All living beings need energy to function. This energy required to drive bodily functions along with other exertions is gained from the food we eat. If you eat more food than your energy usage requires then the food is converted and stored as fat. This is how we gain weight.
You might be thinking how come some people can eat more than others and do less exercise? This is to do with how fast their metabolic rate is. The metabolic rate is how fast your body burns calories (uses energy). The problem with bad dieting is that your body slows the metabolic rate to meet the level of calorie intake. This means when you decide you have reached your goal weight and start eating normally the weight will pile on again. This is due to a starvation system, a survival safety net that causes the body to store all the food it’s given if not given very much. The key to keeping weight off is to eat the right amount for your energy usage and to eat a balance of the three major food groups.
The 3 main food groups that can be used as energy to run the body are fat, protein and carbohydrate. These all are essential for a functional body. They are processed, used and stored differently throughout the body.
Carbohydrates come from starchy (potatoes, bread and rice) and sugary foods (fruit and lollies). Like with many things “carbohydrate” is the term used to describe a substance made up of smaller components; carbohydrates are made up of small units called glucose (a biochemical sugar). Glucose is broken down to use as energy through a process called glycolysis and supplies 100% of the energy needed to run the brain along with most other bodily functions. When not being used for energy glucose either gets stored in the liver as glycogen or converted and stored as fat.
Fat comes from a number of foods and is made up of a unit called lipid. Lipid is used in many important structures throughout the body. Fat is the primary source of energy for most organs and functions of the body and this is because it can yield more than twice the amount of energy as carbohydrates. This means that for the same amount of energy being stored a lot less fat is needed than if stored as glycogen (the stored version of glucose). Fat is a necessary and important form of energy for the body but can cause problems if too much is stored.
Protein comes from foods such as meat or eggs and is made up of units called amino acids. These amino acids make up almost everything in the body and are particularly important for muscle development and repair. As a primary fuel, protein is mostly used as a last resort as it is stored mostly as muscle.
Because sometimes some of these food groups are unavailable the human body has the ability to interchange them. Fat and protein can be converted to glucose if necessary to ensure the brain can be fed energy.
You now know that each nutrient group has an important function within the body and therefore why it is important to maintain an intake of the correct amounts of each. Most of the time the problem with fad diets is that they cut out one of the major food groups.
The human metabolism is a complex system so if you would like more information I can suggest this website however it is advanced and uses some terms you may not be familiar with. A good way to overcome this is by googling the term you are unfamiliar with and looking at the wiki definition as it usually gives a simple idea of what the term means.