Your body uses mostly carbohydrates as well as fats for energy. Because the body doesn’t store carbs efficiently, they’re used first. Carbohydrates turn into glucose, which your body burns immediately or converts to glycogen to be stored in the muscles and liver for between meals. If you eat more calories from carbs or other sources than your body can use, the cells store the excess as fat.
How the Body Uses Carbs
Of the three major nutrients — carbohydrates, fat and protein — the body burns carbs first for energy because they can’t be stored in great quantities. The carbohydrates in food get broken down into glucose, which moves into the small intestine, then the liver and into the blood. As blood sugar rises, the pancreas produces insulin, which signals the cells to take up sugar. Whatever glucose the cells don’t need immediately for energy is stored in the liver and muscles as glycogen. When the blood sugar levels fall — such as between meals — the liver releases glycogen. This cycle keeps your body supplied with a steady source of fuel.
If you have insulin resistance or diabetes, the sugar-insulin cycle doesn’t work properly, leading to too much sugar and insulin circulating in the blood until eventually your body doesn’t produce enough insulin or is resistant to its effects. This is why people with diabetes or prediabetes often track the carbs they eat; eating too many carbohydrates, especially sugars and refined starches, can cause blood sugar and/or insulin to spike to potentially dangerous levels in people with diabetes.
How Carbs Turn Into Fat
When you eat too many calories, especially in the form of sugars and quickly burned starches, your body may reach its storage capacity for glycogen. The liver converts the stored sugars into triglycerides, or fats, so that the excess energy can be transported to the fat cells for longer-term storage. Your fat cells release this energy when needed. If you eat more calories than you burn, your body will continue to store the fat.
Carbohydrates form the base of the U.S. Department of Agriculture’s Food Pyramid, and nutrition experts recommend that most people get between 45 and 65 percent of their calories from carbohydrate-rich foods. If you exercise a lot, you’ll need more carbs for energy. Because they contain fiber and are more filling, you’re less likely to get excess carbohydrates if you eat mostly “good” carbs such as whole grains, fruits and vegetables.