All consumed food is eventually converted to sugar, the energy source for every organ in the body and for every cell in every organ. If too much food is consumed, the extra calories can be stored by the body for later conversion to sugar. Sugar is carried in the blood to all areas of the body, and any cell that is in need of sugar simply uses the sugar present in the blood. How do cells move sugar into their interior from the bloodstream? A substance called insulin, produced by an organ located in the abdomen (the pancreas), is the key that allows cells to obtain sugar from the bloodstream. Insulin is necessary for life.

People, dogs, and cats who do not have insulin have a disease called diabetes mellitus. Diabetes mellitus is and extremely common disease in people, dogs, and cats. There are two common forms of diabetes. The form in which an individual has absolutely no insulin has several names: insulin-dependent diabetes mellitus (IDDM), type I diabetes, and juvenile-type diabetes. The other form occurs when an individual has insulin but either does not have enough or has a condition that interferes with insulin function. It has several names: non-insulin-dependent diabetes mellitus (NIDDM), type II diabetes, adult-onset diabetes. Approximately 10 per cent of people with diabetes mellitus have type I disease and 90 per cent have type II. Approximately 60 per cent of diabetic cats have type I and 40 per cent type II. Virtually 100 per cent of dogs with diabetes mellitus have type I disease.

What happens when an individual has diabetes mellitus? Without sugar constantly being removed from the blood by cells everywhere in the body, the diabetic person, dog, or cat has more and more sugar accumulates that it begins to "spill over" into the urine through the kidneys along with water. Therefore, diabetics urinate large volumes. In dogs and cats, sometimes the first thing that an owner observes is that the pet is no longer "housebroken" or the pet cat begins urinating outside the litter box. Because the volume of fluid lost into the urine of diabetics is excessive, they make up for these losses by drinking more and more water. Because cells throughout the body have lost their access to sugar, they begin to "starve." Individual cells do not see the lack of insulin, they see only a lack of energy (sugar). Therefore, messages are sent out for energy (sugar) and the diabetic begins to eat more and more. Cells still have no access to the sugar, so additional messages for energy are sent out and the body begins to break down fat and muscle for energy (the components of fat and muscle can be converted to sugar by the liver). Although it makes sense to create more energy, the body still cannot use the sugar resulting from this process. The symptoms common to all diabetics now become obvious: they drink excessively, urinate excessively, eat excessively, and lose weight.

When a dog or cat is brought to a veterinarian for any or all of the symptoms known to be associated with diabetes, the diagnosis is quite easily made. Testing is necessary, however, because there are other diseases that cause all or some of the same symptoms. However, once the diagnosis is made, the real problems begin. Treating diabetes mellitus is not easy. It takes skill by the veterinarian, commitment by the owner, and some luck. The cornerstones of treating type II diabetic people include weight loss, exercise, and changes in diet to increase fiber content and to decrease simple sugars. If these factors do not help enough, pills can be given. Use of all these treatments rarely helps type I diabetic people. Type I diabetic people, like 100 per cent of diabetic dogs and 80 to 90 per cent of diabetic cats, require insulin by injection to live. All diabetic dogs and cats do best with good commercial pet food given in two equal-sized meals (cats that tend to "graze"all day should be allowed to continue feeding that way). High-fiber foods may be of benefit but are not critical.

Unfortunately, although insulin has been available to treat diabetics for more that 70 years, it must still be given by injection. Your veterinarian will teach you how to give injections to your pet. It is understood that this can be quite intimidating for owners and that your pet will feel the needles. However, once you have done this for a few weeks, you will become quite competent and your pet will accept the tiny pinpricks. Don’t give up! Your pet can live an extremely healthy life despite requiring insulin. There are several different kinds of insulin. Regular (R; crystalline) insulin is the most potent and the shortest acting; Ultralente (U) is the least potent and the longest acting; protamine zinc insulin (PZI) is similar to Ultralente; neutral protamine Hagedorn (NPH;N) insulin is less potent and longer acting than regular but more potent and shorter acting that Ultralente; and Lente (L) is 30 per cent regular and 70 per cent Ultralente and has effects similar to those of NPH. One insulin may not work satisfactorily in your pet but another my work well. It takes time to determine which insulin and which insulin dose are best for an individual cat or dog. Whereas most cats and dogs respond best to insulin given twice daily (do not try to give the insulin exactly every 12 hours; it is not necessary), some do well with only one injection per day.

Remember the most important goal in treating a diabetic dog or cat: we want the pet to be happy and stable. No diabetic pet becomes absolutely normal.

Finally, regardless of treatment, virtually 100 per cent of diabetic dogs (not cats) develop cataracts and become blind within the first 6 to 24 months; this is inevitable and not a reflection of the job you have done in treating your pet.