Table sugar, or sucrose, is a dietary sweetener derived from a variety of plant sources, including sugarcane and sugar beets. Nutritionists classify sucrose as a simple sugar, because your body easily and quickly digests and assimilates it. The sucrose molecule is a disaccharide composed of two simple monosaccharides, glucose and fructose. According to Elson Haas, M.D., glucose is the principal form of fuel used by your cells to produce energy.
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Before your body can convert sugar to energy, you must first digest and absorb it. When you consume sucrose – sugar is nearly ubiquitous in the American diet – it quickly separates into its two monosaccharide constituents by an enzyme called sucrase. Your bloodstream readily absorbs both glucose and fructose through the lining of your intestine. From there, the bloodstream carries them to your liver, where fructose converts to glucose. Hence, sucrose is a rich source of glucose, which all of your cells can use for energy.
Your liver helps to regulate the amount of glucose in your blood and provides a continuous supply to meet your energy needs. When your cells require energy, they absorb glucose from your bloodstream and break it into two molecules of pyruvate, which then transfer into the mitochondria – the "furnaces" in your cells – where pyruvate converts to acetyl-CoA. Within the mitochondria, acetyl-CoA underoes processing via two metabolic pathways – the citric acid cycle and the electron transport chain. This yields adenosine triphosphate, or ATP, the source of energy for all metabolic processes. This oxidative metabolism of one glucose molecule yields 36 molecules of ATP, according to Dr. Michael Gregory at State University of New York.
If your sugar consumption exceeds your body's immediate energy needs, glucose converts to glycogen and becomes stored in your liver and muscles. Once these organs reach their capacity to store glycogen, excess glucose first converts to fatty acids and then to triglycerides, which become stored in your adipose tissue. When the glucose from your diet does not meet the energy needs of your cells – during fasting or exercise, for example – your body can quickly break down glycogen to produce glucose. Similarly, triglycerides break down into fatty acids and then to acetyl-CoA, which enters your mitochondria for "burning."
Sugar, by virtue of its easy digestibility and high glucose content, is a quick source of energy for your cells. However, the over-consumption of sugar is one factor contributing to the obesity epidemic in developed countries. The U.S. Department of Agriculture reports that the average American consumes more than 150 pounds of sugar annually, and the typical American diet provides around 32 added teaspoons of sugar each day. Ten teaspoons daily is the recommended limit. Complex carbohydrates -- whole grains, fruits and vegetables -- provide ample supplies of glucose for your energy needs while also furnishing an array of other useful nutrients.