Carbohydrates represent the basic form of the body's energy source. They are able to both be used by the system after digestion and also to be stored by the body for later use. Dieters are concerned with carbohydrates because in storage, carbohydrates can either be converted to glycogen or into fat.  When the cells have reached their glycogen storage limits, the carbohydrates become fat. Some athletes "carbo load" before events, because the extra carbs will be used as needed energy.
In the human body, carbohydrates aren't 100% necessary, because proteins can also be converted into carbohydrates;  cats are very adept at doing this also . Carbohydrates themselves need less water for digestion than do proteins and/or fats, which are the building blocks of cells and tissues. Using them as sources of energy in this way may not be wise. See Diet for more information.
Simple and complex carbsEdit
They are sorted into two basic categories--simple carbohydrates and complex carbohydrates. The difference between the two is this: simple carbs have much shorter chains than complex ones.  This means they are broken down by the body's digestion easier, making them quickly absorbed. Complex ones have longer chains, which take longer for the body to break down by digestion. They take longer to be absorbed because the breaking down process for them is more complex. 
What this means for someone with diabetes is that in eating simple carbs, such as sugar, products containing sugar, milk, fruit, etc., the rise in blood glucose levels will begin quite soon after the food has been eaten.  It will also not last for an extended period of time.
When dealing with hypoglycemia, the simple carbs (like sugar and corn syrup) are desirable, because they are able to work rapidly to raise blood glucose levels. Since they work quickly, they are also expended quickly, with possibly little or nothing left to keep blood glucose levels from dropping again. Eating or feeding something with complex carbs in it shortly after the start of recovery from the hypoglycemia makes certain that there will be longer-lasting carbohydrates available to keep blood glucose levels up, after the sugar or corn syrup has worn off.
Simple carbs can also be referred to as "fast carbs" because they act quickly. 
Eating complex carbs  such as potatoes and grains, means that the rise in blood glucose levels from them will begin later than with the simple carbs. The rise from complex carbs  is also longer lasting.
Complex ones can be termed "slow carbs" because they raise blood glucose slowly.
Glycemic index/glycemic loadEdit
Most simple carbs  are rated quite high on the glycemic index. . The glycemic index is defined as the speed of digestion and rate of glucose absorption  An alternative measurement system to the glycemic index is called the glycemic load. . Many people with diabetes count carbohydrates, with the emphasis on the total of how many carbs they eat in a day 
Intervet  brings up an interesting point re: the carbohydrates present in the low-carb diet for cats. Drawing from Dr. Greco's 2001 study as reference,  they suggest that the carbohydrates of the low-carb foods chosen should be as low in the glycemic index  as possible. This is echoed in the "Feeding the Diabetic Patient" presentation from Ohio State University's Endocrinology Symposium in 2006.  Both sources recommend low-GI foods like barley and whole grains as carbohydrate sources for cats.
Soluble and insoluble carbsEdit
Soluble carbohydrates are grains, such as wheat, rice, barley, oats and corn. When cooked and present in pet foods, digestion is easy and rapid.
Insoluble carbohydrates are those we refer to as fiber, which pass through the intestinal tract without being digested.  Bran,corn and its by-products, soy fiber, and beet pulp  are some examples found in pet foods.
- ↑ Conversion of Carbohydrates. Weightlossforall.com.
- ↑ Carbohydrates. Wikipedia.
- ↑ Diabetes, Obesity & Diet. Manhattancats.
- ↑ Simple & Complex Carbohydrates. Weightlossforall.com.
- ↑ 5.0 5.1 5.2 5.3 Elliott, Denise (2006). Feeding the Diabetic Patient-Page 34. OSU Endocrinology Symposium.
- ↑ Hypoglycemia Symptoms. Diabetesnet.
- ↑ Blood Glucose & Complex Carbohydrates. Weightlossforall.com.
- ↑ Blood Glucose Rise With Complex Carbohydrates. Carbs-information.com.
- ↑ Simple Carbohydrates. Carbs-information.com.
- ↑ Glycemic Index. Carbs-information.com.
- ↑ Glycemic Load. Wikipedia.
- ↑ Diet: Carbohydrate Counting. RemedyFind.com.
- ↑ What to Feed the Diabetic Patient (Page 11) References (Page 16). Intervet.
- ↑ Greco, Deborah (2001). Comparing High Protein/Low-Carbohydrate to High-Fiber Diet in Feline Diabetes mellitus.
- ↑ Glycemic Index-How It's Measured. Carbs-information.com.
- ↑ Glycemic Index of Foods-Glycemic Index Values. Carbs-information.com.
- ↑ Fiber in Pet Foods. Pet Education.
- ↑ Beet Pulp in Pet Foods. Pet Education.