How the body controls blood sugar, what goes wrong in diabetes, and everyday habits that help keep blood sugar steady.
Your body runs mainly on glucose, a sugar that comes from the carbohydrates you eat. Keeping the level of glucose in the blood within a healthy range is one of the body's most important jobs. When that system stops working properly, the result is diabetes. Here is how blood sugar is controlled, what goes wrong, and what you can do day to day.
How blood sugar is controlled
When you eat, carbohydrates are broken down into glucose, which passes into the bloodstream. As blood sugar rises, the pancreas releases the hormone insulin. Insulin acts like a key, letting glucose move out of the blood and into your cells, where it is used for energy or stored for later, in the liver and muscles and, if there is more than the body needs, as fat.
Between meals and overnight, when blood sugar falls, the pancreas releases a different hormone, glucagon, which signals the liver to release stored glucose. Together, insulin and glucagon keep blood sugar fairly steady.
What goes wrong in diabetes
Diabetes is a condition in which blood sugar stays too high, because the body doesn't make enough insulin, can't use it well, or both. Over time, high blood sugar damages blood vessels and nerves and can lead to heart disease, stroke, kidney disease, vision loss and nerve damage in the feet.
- Type 1 diabetes is an autoimmune condition in which the immune system destroys the insulin-making cells of the pancreas. People with type 1 diabetes need insulin every day. It is not caused by diet.
- Type 2 diabetes, by far the most common type, usually starts with insulin resistance: the body's cells don't respond well to insulin, so glucose can't get in easily. At first the pancreas makes extra insulin to compensate. Over time it can't keep up, and blood sugar rises. Excess weight, especially around the waist, inactivity, family history and age all raise the risk.
- Gestational diabetes develops during pregnancy and usually goes away after birth, but it raises the risk of type 2 diabetes later.
Prediabetes means blood sugar is higher than normal but not yet high enough for a diagnosis of type 2 diabetes. It is very common and often has no symptoms. The good news is that prediabetes can often be reversed: modest weight loss and regular physical activity substantially lower the chance of developing type 2 diabetes.
Signs to watch for
High blood sugar may cause increased thirst, frequent urination, tiredness, blurred vision, slow-healing sores and unexplained weight loss, but many people have no symptoms at all. Ask your doctor about a blood sugar test, especially if you are over 35, are overweight, or have a family history of diabetes.
Everyday habits that help
Whether you want to lower your risk or are managing diabetes with your health care team, the same habits help:
- Choose fiber-rich carbohydrates. Vegetables, beans, lentils, whole grains and whole fruit raise blood sugar more gradually than white bread, pastries and sweets.
- Cut back on sugary drinks. Soda, sweet tea, energy drinks and large amounts of juice raise blood sugar quickly and add a lot of sugar.
- Pair carbohydrates with protein, fat or fiber. Eating them together, for example fruit with nuts or yogurt, slows the rise in blood sugar.
- Watch portions of starchy foods such as rice, pasta, bread and potatoes. A plate that is half vegetables, a quarter protein and a quarter starch is a simple guide.
- Move more. Physical activity helps your muscles use glucose and makes your body more sensitive to insulin. Even a short walk after meals helps.
- Aim for a healthy weight. Losing even a modest amount, around 5 to 7 percent of body weight, can make a big difference for people with prediabetes.
- Sleep well and manage stress. Both affect blood sugar.
Sugar in itself doesn't cause diabetes, but diets high in added sugar, especially from drinks, are linked with weight gain and a higher risk of type 2 diabetes. If you have diabetes, your doctor or a diabetes educator will tell you whether and how to monitor your blood sugar; most people without diabetes don't need to. Read more about carbohydrates and weight loss.
Sources
- Insulin resistance and prediabetes (National Institute of Diabetes and Digestive and Kidney Diseases)
- Steps for losing weight (US Centers for Disease Control and Prevention)
Last reviewed November 2026. This article is general information, not medical advice.