The Different Types of Carbohydrates

How Simple Carbs and Complex Carbs Affect Blood Sugar

oatmeal and fruit
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Keeping track of carbohydrates in the diet is an important part of managing type 2 diabetes. It's also helpful to have some knowledge of the difference between the two types of carbohydrates: simple carbs that are found in everything from table sugar to fruit and complex carbs, or starches, that occur in foods such as whole grains and starchy vegetables like sweet potatoes.

Each type of carb impacts blood glucose levels somewhat differently. So whether you're managing the carbohydrates in your diet by counting them, watching portions using the Plate Method, or following another carb tracking protocol, understanding the effects of each type of carb can help you to make the most of your treatment plan, control your blood sugar levels, shed excess pounds and/or maintain a healthy weight, and help prevent complications.

Carbohydrates 101

Carbohydrate is one of the three macronutrients in food that provide fuel for the body to function properly. The other two are protein and fat. During digestion, all three are broken down into the elements the body can use for energy: Protein is reduced to amino acids and fat is reduced to fatty acids, both of which are then stored for future use.

Carbohydrates, on the other hand, are broken down into glucose (sugar) which, after a quick stop in the liver, enters the bloodstream and is immediately available to be taken up by cells for energy. This is why eating carbs can affect blood sugar levels so quickly and dramatically.

It's also why it's so important for people with type 2 diabetes to keep tabs on the carbs they eat. In this disease, the pancreas does not produce enough of a hormone called insulin that regulates blood glucose levels or else the body has become resistant to the effects of insulin. In both cases, glucose can build up in the bloodstream.

Simple Carbs

Simple carbohydrates are, as the name implies, simple structures. In chemical terms, they're small molecules consisting of a single monosaccharide or of two monosaccharides linked together—what are called disaccharides.

Glucose, the type of sugar the body and brain use for energy, is a monosaccharide, as are fructose and galactose. The disaccharides include lactose, sucrose, and maltose.

Simple carbs are fairly easy for the body to digest: Most are processed in the small intestine, where enzymes break them down into individual components that then pass through the intestinal walls into the bloodstream to be used for energy.

Any sugar that isn't used right away is converted to fat and stored. This is why eating foods with lots of added sugar can contribute to weight gain.

Examples of Simple Carbs

Many foods containing naturally occurring simple carbohydrates are rich sources of vitamins, minerals, antioxidants, fiber, and other nutrients and so they can—and should—be a part of a diabetes-friendly diet. Examples include:

  • Fruit, including dried fruit and unsweetened fruit juice
  • Dairy products
  • Certain vegetables
  • Certain grains

Fruits are valuable sources of vitamins, minerals, antioxidants, and fiber, as are vegetables and grains. By the same token, dairy products offer protein, calcium, and vitamin D.

However, not all simple sugars are processed at the same rate. For instance, because whole fruit contains fiber, the fructose it contains is digested and absorbed more slowly than, say, sucrose, and will have a less dramatic effect on blood glucose levels.

Complex Carbs

Complex carbohydrates, known as oligosaccharides and polysaccharides, are made up of longer, more complex chains of sugar molecules and so it takes the body longer to digest them than to process simple carbs. Some complex carbohydrate foods contain fiber, vitamins, and minerals and take longer to digest. This means they have a less immediate impact on blood sugar, causing it to rise more slowly.

Examples of Complex Carbs

Certain complex carbs are better choices than others. The healthiest complex carbohydrates are those that have not been processed or refined:

  • Whole grains such as brown rice, wild rice, oatmeal, whole-grain (rather than pearled) barley, bulgur (which is made from cracked wheat), and farro
  • Grain-like foods such as quinoa (a seed) and buckwheat (a grass)
  • Starchy vegetables including potatoes, sweet potatoes, and corn
  • Non-starchy vegetables—everything from asparagus to zucchini
  • Beans and legumes like lentils, kidney beans, and chickpeas

Note that all of these foods are excellent sources of fiber. Fiber helps keep blood sugar levels from spiking too high, helps regulate cholesterol levels, and is important for intestinal health.

With complex carbs, it's best to avoid or limit grains that have been refined and processed foods made from refined grains. "Refined" means two of the three elements of each kernel of grain have been removed—namely the bran and the germ, both of which are important sources of fiber, healthy fats, and nutrients.

The part of the kernel that's left, the endosperm, is starchy and has less fiber and nutrients. Sometimes vitamins and minerals are added back into refined grains (in which case they typically are labeled as enriched), but this is no substitute for grains that are left intact.

Processed foods made from refined grains include:

  • Bagels
  • Cakes, cookies, doughnuts, muffins, pastries, and other sweet baked goods
  • Cereals made from refined grains and highly sweetened
  • Crackers
  • Hamburger or hot dog buns
  • Pancakes and waffles
  • Pizza dough
  • Rice snacks
  • Soft sandwich bread 
  • White rice and pasta

Note that many of these foods are also sources of added sugar, further making them less than ideal for managing blood glucose.

Balancing Simple and Complex Carbs

How different people respond to specific types of carbs, and even to individual foods, can vary widely. This is one reason there's no such thing as a standardized treatment protocol for diabetes.

That said, when planning meals and snacks, it's generally advisable to focus on getting most of your carbohydrates—both simple and complex—from natural, unrefined, and unprocessed sources, like fresh fruits and vegetables, whole grains and products made from whole grains, low-fat dairy products, and legumes. This way you can feel certain you're getting foods that are rich in nutrients, high in fiber, low in calories and saturated fat, and more likely to help you to control your blood sugar and manage your diabetes.

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