Consuming sucrose and other types of sugar appear to raise energy levels in proportion to the amount consumed. In fact, consuming sugar in large enough amounts can result in a burst of energy known as a sugar high that ends in a sharp drop in energy levels, termed a "crash." Although these effects are similar to those from chemicals like caffeine, sugar is not a stimulant. Instead, it is what the body uses as fuel.
Sugar as Energy
Somatic cells require glucose for energy. When the body derives glucose from foods, the pancreas releases insulin, signaling cells to absorb the glucose. This fuels cells throughout the body, resulting in a discernible increase in energy. The liver converts excess glucose to glycogen, which the body stores in muscles and other tissue. Once the body stores 12 hours worth of glycogen, the liver converts the remaining glucose to fat.
Sources of Sugar
Glucose is a type of sugar that the body derives or synthesizes from food during metabolism. The body draws glucose from carbohydrates most readily, although it can also convert proteins and fats into glucose. Carbohydrates include monosaccharides, or simple sugars, like fructose and galactose; disaccharides, which are combinations of fuctose, galactose and glucose; starches; and cellulose, or fiber, although fiber is indigestible and thus does not provide energy. The body derives glucose fastest from fructose, typically within 15 minutes, according to Sarí Harrar and Julia VanTine in "Prevention's the Sugar Solution." However, it can take up to eight hours to absorb glucose from fat or protein.
Upper and Lower Limits
Aside from when it's the result of a medical condition, low blood sugar, or hypoglycemia, is rare. However, hypoglycemia can result in coma or death. High blood sugar, which often occurs from high sugar or carbohydrate consumption, can cause strokes, heart disease, damage to the overall circulatory system, eye damage, nerve damage and other complications. Accordingly, it is essential that blood sugar remains within a certain range. Therefore, although sugar is an essential source of energy for the body, it has the capacity to be either deficient or toxic, depending on its serum blood levels. Specifically, blood glucose levels below 40 mg per deciliter and above 100 mg per deciliter are dangerous enough to cause severe health complications or death.
Several conditions and other factors can alter the way that your body responds to sugar. Diabetes is the primary cause of sugar-related health complications. Diabetes is a condition in which the pancreas does not excrete enough or any insulin, or somatic cells do not respond to it. In both cases, the body is unable to utilize sugar, leaving it to collect in the bloodstream. The reverse can also occur frequently in those with diabetes, as medication and supplements meant to bolster or replace natural insulin reduces blood serum glucose to dangerously low levels. Another confounding factor is obesity, which renders the body less responsive to insulin, resulting in effects similar to pancreatic dysfunctions. Moreover, stress, injury and physical exertion, including from exercise, trigger the release of epinephrine, which prompts the liver to flood the bloodstream with glucose from its glycogen stores to cause a quick and sharp rise in energy, which can occur even in the absence of recent food or sugar consumption.