More on Metabolism…

Proteins, carbohydrates, and fats move along intersecting sets of metabolic pathways that are unique to each major nutrient. if all three nutrients are abundant in the diet— carbohydrates and fats will be used primarily for energy proteins provide the raw materials for making hormones, muscle, and other essential biological equipment.

Proteins in food are broken down into pieces (called amino acids) used to build new proteins with specific functions catalyzing chemical reactions, facilitating communication between different cells, or transporting biological molecules When there is a shortage of fats or carbohydrates, proteins can also yield energy.

Fats typically provide more than half of the body’s energy needs. Fat from food is broken down into fatty acids, which can travel in the blood and be captured by hungry cells. Fatty acids that aren’t needed right away are packaged in bundles called triglycerides and stored in fat cells, which have unlimited capacity.

Carbohydrates can only be stored in limited quantities, so the body is eager to use them for energy. The carbohydrates in food are digested into small pieces—either glucose or a sugar that is easily converted to glucose—that can be absorbed through the small intestine’s walls. After a quick stop in the liver, glucose enters the circulatory system, causing blood glucose levels to rise.

Once the cells have had their fill of glucose, the liver stores some of the excess for distribution between meals should blood glucose levels fall below a certain threshold. If there is leftover glucose beyond what the liver can hold, it can be turned into fat for long-term storage so none is wasted. When carbohydrates are scarce, the body runs mainly on fats. If energy needs exceed those provided by fats in the diet, the body must liquidate some of its fat tissue for energy.

Insulin is incredibly important to the way the body uses the glucose that foods provide. Insulin functions are: To enable glucose to be transported across cell membranes To convert glucose into glycogen for storage in the liver and muscles To help excess glucose be converted into fat To prevent protein breakdown for energy

Glycemic index

Glycemic index (also glycaemic index, GI) is a ranking system for carbohydrates based on their immediate effect on blood glucose levels Carbohydrates that break down rapidly during digestion have the highest glycemic indices. Such carbohydrates require less energy to be converted into glucose, which results in faster digestion and a quicker increase of blood glucose.

Carbohydrates that break down slowly, releasing glucose gradually into the blood stream, have a low glycemic index. A lower glycemic index suggests slower rates of digestion and absorption of the sugars and starches in the foods and may also indicate greater extraction from the liver and periphery of the products of carbohydrate digestion.