Diabetes mellitus occurs when the body doesn’t
produce adequate amounts of insulin or becomes less responsive to insulin. Insulin is a hormone
made by the pancreas with many functions, but its main purpose is to tell cells to take
up glucose from the bloodstream. Glucose is the main energy source for the body’s cells
and without adequate insulin or the inability to properly respond to insulin, glucose doesn’t
get taken up properly. Thus, blood glucose levels increase in diabetes mellitus leading
to high blood sugar levels or hyperglycemia. Hyperglcemia leads to sugar “spilling over”
into urine resulting in increased urination. The word “mellitus” in diabetes mellitus means
“honey-sweet” in Latin and differentiates this type of diabetes from a rarer disease,
called diabetes insipidus, which has similar signs but doesn’t result in sugar or glucose
in the urine. To compensate for the increased water lost with the additional urination,
thirst also increases. Without treatment of diabetes mellitus, the body relies on fat
for energy resulting in the production of toxic acids known as ketones. Ketones can
also spill over into the urine. Left untreated diabetic ketoacidosis can lead to coma and
death. Insulin overdose can also be dangerous as
it can lead to a very low blood glucose level or severe hypoglycemia. The greatest risk
of insulin overdose is when a pet has not eaten or has not eaten well and still is given
their full insulin dose. This risk is more common in pets as blood glucose is not typically
measured to enable adjustments in the insulin dose given. Thus, changes in the diet or food
may not be made in newly diagnosed Type 1 diabetics to make sure that the food that
is normally fed is readily eaten and insulin overdose is less likely. In humans many of the long-term effects of
hyperglycemia and poor glucose control, such as kidney failure, are not recognized in pets.
Even with good control, some serious conditions are unfortunately expected to develop in pets
like blindness from cataracts in dogs. Therefore, dietary therapy in pets is mainly designed
to reduce the likelihood of pets being so poorly controlled as to be at risk of life
threatening situations like diabetic ketoacidosis, especially in the dog and in the cat to also
potentially eliminate the need for insulin injections. Pets with diabetes mellitus drink more water
and urinate more than normal (referred to as polydipsia and polyuria or PU/PD). PU/PD
coupled with unintended weight loss raises the concern that a pet might have diabetes
mellitus. The diagnosis of diabetes mellitus relies typically on measuring blood glucose
and looking for glucose and possibly ketones in the urine. Hyperglycemia can occur with
stress especially in the cat, such as during a visit to the veterinarian, so the presence
of glucose in the urine along with more advanced tests like measuring fructosamine can give
a better sense of the typical blood glucose levels. If blood glucose levels are high,
not due to stress in the cat, along with glucose in the urine, a diagnosis of diabetes mellitus
is made. All dogs with diabetes mellitus need insulin injections for the rest of their lives
as dogs only develop Type 1 (aka insulin-dependent) diabetes mellitus. Cats may have Type 1 or
Type 2 (aka non insulin-dependent) diabetes mellitus. Therefore they may need insulin
injections or just oral medications, especially if coupled with loss of any extra body weight. Losing extra body weight can potentially cause
insulin dependent diabetic cats to no longer need injections of insulin. This is because
weight loss can make the body more sensitive to insulin which may mean that insulin made
solely by the body is enough to get an appropriate uptake of glucose. For a more comprehensive
discussion on how to nutritionally manage weight, please see the weight management video
in this series. Key strategies discussed in that video include feeding less calories than
are needed, nutrient enhancement, energy density reduction, caloric distribution modifications,
increased feeding frequency & treating, and providing supplemental compounds especially
L-carnitine. In the dog, weight loss will not eliminate the need for insulin injections,
but may reduce the needed dose as well as help with overall blood glucose level or glycemic
control. All other nutritional therapy strategies are for fine tuning of glycemic control and
may not be tried especially if they may lead to reduced appetite. Dietary fiber can help reduce the absorption
and rate of absorption of glucose from food. Muting or slowing glucose absorption can lead
to better glycemic control. Unfortunately, high dietary fiber may not be as palatable
to some pets and/or may not be tolerated. Some foods inherently have a higher fiber
content like legumes and may be used for this express purpose or more concentrated fiber
may be supplemented into the diet. Dietary fiber has an effect on stool volume and quality.
Many pets have improved stool quality with higher dietary fiber, and fermentable fiber,
or prebiotics, may be beneficial to GI flora or microbiota. At the same time, the occasional
pet may not tolerate very high dietary fiber levels and adjustments in amount may be needed
based solely on stool quality in those cases. Generally, mixed fiber sources that come from
natural sources like psyllium seed husk or legumes as well as more purified insoluble
fiber sources like cellulose are better tolerated than just purified soluble fibers like from
gum. Glycemic index is a measure of how quickly
blood glucose rises following consumption of a particular amount of food in humans.
The lower the glycemic index, the less the food causes a rise in blood glucose. As different
foods have different carbohydrate levels, some differences in glycemic index are largely
related to the carbohydrate content of the food. Much of the difference can also be attributed
to the fiber content of the food. For example, legumes that are higher in protein, and thus
lower in carbohydrate, and also higher in dietary fiber than white rice not surprisingly
have a lower glycemic index than white rice. Therefore, certain carbohydrate sources may
be preferentially used in pet food appropriate for the nutritional management of diabetes
mellitus. There is some overlap in folks minds with
glycemic index and the term “complex carbohydrate.” Starch is a complex carbohydrate, meaning
that it is made up of long chains of molecularly linked glucose. This means that it takes longer
to digest and release the glucose or sugar the complex carbohydrate contains compared
to eating a food rich in simpler sugars like fruit. Fortunately, most pets do not consume
a great deal of foods really rich in simple sugars like granulated sugar, syrups, candy,
or juice. In diabetic pets, simple sugars should be avoided and fruits should be carefully
selected if blood glucose control has been challenging. Reducing the amount of total dietary carbohydrate
may also be helpful in managing diabetic pets as eating less dietary carbohydrate reduces
the total amount of glucose that is digested and is available to raise the blood glucose
level. In cats there is some evidence that weight loss and possibly a low carbohydrate
diet may revert a diabetic cat into not needing insulin injections. This is an active area
of research, but if tolerated a diet that is lower in carbohydrate and higher in protein
and/or fat may be indicated. Not all cats will tolerate such a diet, so higher fiber
or less energy dense foods that are high in carbohydrate may also be suggested to induce
weight loss. Dietary therapy in diabetic pets is often
fine-tuning or tried when other medical therapies have not resulted in good glycemic control.
Glycemic control may be assessed with an all day blood glucose curve or measuring fructosamine
which gives one a sense of the average level of control over several weeks.Thirst and urination
at home may also be monitored and noted. Occasionally, a veterinarian may train one to measure a
pet’s blood glucose level at home. Dietary therapy may be instituted and adjusted based
on glycemic control, and if weight loss is needed, to achieve an ideal body condition
in diabetic pets. If glycemic control is not improved with diet modifications, then a normal
maintenance food or a food appropriate for any other concurrent conditions may be fed.
With the right combination of medical and dietary treatments, pets can often live quite
comfortably with diabetes mellitus.