Glucose is a nutrient molecule that your cells can use to provide for energy needs. You need glucose --- in particular, the brain depends upon a steady supply of glucose to remain functional. Too much glucose, however, leads to an excess of available energy in the body. The cells respond to this by storing excess glucose in the form of fat, which can lead to obesity.
Glucose
You consume glucose almost anytime you consume carbohydrate-containing food. Glucose occurs in nature on its own --- it's found in fruit, for instance --- but more commonly, it occurs in nature chemically bonded to other molecules of glucose or to related sugar molecules. For instance, table sugar consists of a molecule of glucose chemically bonded to a molecule of the related sugar fructose. Starch, which goes by the chemical name amylose, is a chain of hundreds of glucose molecules chemically bonded together.
Digestion of Foods
Regardless of the form in which you consume glucose, your digestive tract quickly breaks sugars and starches down into their constituent compounds --- you digest starch into individual glucose units, for instance. The intestine then absorbs the glucose into the bloodstream, and your cells can take up molecules of the sugar from there. Cells can't absorb glucose from the bloodstream without the help of the hormone insulin, which your pancreas produces. If you eat a glucose-containing food and your blood glucose level rises, the pancreas releases insulin to signal cells to take up glucose from the blood.
Glucose Storage
Your cells can do many things with glucose; what they do depends upon the availability of energy. If your cells need energy right away, they burn glucose. If immediate energy needs are low, cells store extra glucose. The liver and muscle cells can assemble glucose molecules into a long chain of glucose units called glycogen, explains Dr. Lauralee Sherwood in her book "Human Physiology." Alternately, cells can convert glucose into a molecule called acetyl-CoA, which they then use to build fat. You store fat in adipose cells.
Obesity
If you consistently consume more glucose than you need to meet your cellular needs, you'll store much of the excess glucose in the form of body fat. This increases your weight and your body fat percentage, eventually leading to obesity. The National Heart Lung and Blood Institute defines obesity as having a BMI --- your weight in kilograms divided by your height in meters squared --- greater than 29.9. Obesity puts you at greater risk for Type 2 diabetes, arthritis and cardiovascular disease.
Insulin Signal
Depending upon the rate at which your body absorbs glucose from food, you may be more or less likely to store excess glucose as fat. Eating simple sugars or carbohydrate --- which is essentially pure glucose --- causes blood sugar to rise quickly. This increases the strength of the insulin signal from the pancreas, and contributes to increased fat storage. Consuming carbohydrate in combination with fiber --- as you do when you eat whole grain --- reduces the rate at which you absorb glucose. This decreases the strength of the insulin signal, and reduces the extent to which you store excess glucose as fat.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- NHLBI: Obesity
