From the moment a bite of food enters the mouth, each morsel of nutrition within starts to be broken down for use by the body. So begins the process of metabolism, the series of chemical reactions that transform food into components that can be used for the body's basic processes. Proteins, carbohydrates, and fats move along intersecting sets of metabolic pathways that are unique to each major nutrient. Fundamentally—if all three nutrients are abundant in the diet—carbohydrates and fats will be used primarily for energy while proteins provide the raw materials for making hormones, muscle, and other essential biological equipment. Carbohydrates, on the other hand, can only be stored in limited quantities, so the body is eager to use them for energy. "We think of carbs as the [nutrient] that's used first,"<span>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. The body's cells gobble up this mealtime bounty of glucose more readily than fat, </span>
Population density is the average number of individuals in a population per unit of area or volume. For example, a population of 100 insects that live in an area of 100 square meters has a density of 1 insect per square meter.
