Bagels are an example of a fast carbohydrate, often stored as body fat
Carbohydrates are commonly referred to as fast or slow, based on how quickly your body digests them. Slow carbohydrates are those that help keep blood sugar levels stable and provide long-lasting energy. Fast carbohydrates, on the other hand, can cause spikes in blood sugar and consequently promote weight gain. You can boost your metabolism by limiting the fast carbohydrates that give you a short burst of energy followed by a crash and increasing the slow carbohydrates that provide sustained energy.
Understanding the Glycemic Index
The glycemic index rates how quickly a given carbohydrate causes blood sugar levels to spike. The faster blood sugar spikes, the more insulin the body releases. Insulin is a hormone that helps regulate blood sugar levels. When the blood contains too much sugar, your body releases more insulin to help remove it. Eventually, if blood sugar levels are chronically high, the body can become insulin resistant, a condition that commonly leads to type-2 diabetes. To prevent this, consume carbohydrates that rank low on the glycemic index and don't cause spikes in blood sugar.
Fast Carbs Make You Fat
Avoid fast carbs, because they cause spikes in blood sugar, which then trigger a surge in insulin. The insulin subsequently works to store the excess blood sugar in the form of body fat. Examples of foods that have a high glycemic index include potatoes, candies, sugary breakfast cereals, couscous, white-flour pasta, fruit juices, white bread, pretzels, saltine crackers, white rice, macaroni and cheese, bagels and instant oatmeal. Generally, any high-sugar or processed carbohydrate ranks high on the glycemic index and should be avoided.
Slow Carbs Give You Energy
Slow carbohydrates are ideal for energy, because they trigger a slow rise in blood sugar and a gradual release of insulin, which steadily pulls sugar from the blood for energy. Foods that rank low on the glycemic index are low-sugar, unprocessed or minimally processed carbohydrates. One hundred percent stoneground whole wheat bread, for example, is low on the glycemic index, in contrast to the much higher ranking for white bread, which comes from the same raw materials but has much more processing. Other examples of low glycemic index foods include rolled or steel cut oatmeal, oat bran, most fruits, nonstarchy vegetables, pasta and most legumes, including kidney beans, black beans, lentils, pinto beans and chickpeas.
Slow Carbs for a Fast Metabolism
Although it may sound counterintuitive, fast carbohydrates slow down the metabolism, whereas slow carbohydrates can help speed up your metabolism. Nutrition and fitness expert Dr. Len Lopez notes that eating slow-burning, low glycemic index carbohydrates can help you lose weight and keep it off by holding your body in a fat-burning zone throughout the day. High glycemic index carbs do just the opposite and trigger fat storage, which in turn slows down the metabolic rate.