Carbohydrates, Metabolism & Weight Gain

Low-carbohydrate diets place the blame for weight gain on the body's metabolism of carbs. This has some basis in fact, but it's not that simple. Between the time you eat a high-carbohydrate food and the appearance of another pound on the scale, a complicated process takes place. The nature of the process depends on what kind of carbohydrates you've eaten.

Types of Carbohydrates

Carbohydrates are either simple, complex or fiber. Simple carbs, found in sugar, fruit and milk, are the easiest for your body to digest because they involve only a single molecule. Complex carbs, such as those found in legumes, starchy vegetables and whole wheat foods, consist of chains of molecules. Fiber is a complex carbohydrate consisting of a chain of molecules your body can't break down at all. Fiber foods include nuts, grains and vegetables.

How Carbs Are Digested

Your system does not have to reduce simple carbs to single molecules through digestion. They're already small enough that they can pass into your bloodstream with a minimum of fuss. However, your digestive system must break complex carbs apart into separate molecules for absorption into your blood. Fiber isn't digestible at all. It passes through your system as is. Soluble fiber absorbs fats and some glucose and takes these along with it, helping to regulate blood sugar. Insoluble fiber moves food and waste through your system, maintaining regularity.

How Carbs Are Metabolized

Your body metabolizes all carbs except fiber into glucose, or blood sugar. All your cells can make use of glucose, so it's your body's preferred source of energy. Because simple carbs don't need a great deal of processing, they convert to glucose and hit your bloodstream in a rush. Glucose from complex carbohydrates reaches your bloodstream more slowly because the conversion process is more involved. When glucose begins moving through your bloodstream, this signals your pancreas to release insulin. Insulin sends the glucose to your liver and muscles for storage as glycogen for potential use later. If you stop eating carbs, your body will release glycogen back into your bloodstream for energy.

How It Affects Your Weight

Your liver and muscles can store no more than about 500 g of glycogen, depending on your gender. If you consume a great many carbohydrates and glucose still remains in your bloodstream after those 500 g or so have been stored as glycogen, your body will convert the excess to fat. Fat is your body's backup source of energy in case it ever runs out of both glucose and glycogen. If you overeat carbohydrates on a regular basis, your body will continue converting the overabundance to fat and will keep hoarding it. Eventually, the fat will add up and result in weight gain.