Diabetes in pets: what are the symptoms and causes and is there a cure?

Pete Wedderburn explains diabetes in dogs and cats, and why diet is relatively unimportant

Mon, 18 Oct, 2021 - 16:30

Most people have friends or relatives who suffer from diabetes, but did you know that this is a common condition in dogs and cats as well? But diabetes is not the same in humans, dogs and cats: there are similarities, and there are differences.

Comparative pathology was a topic that I loved when at vet college: the science of comparing human and animal diseases. As vet students, we were taught this at a basic level: it was enough for us to learn that most human diseases happen in animals, and vice versa. And we also learned that there are key differences between species. Diabetes is a good example. Most people don't realize this, and when their pet is diagnosed with diabetes, they wonder if they caused the issue by giving too many sugary biscuits. The truth is that diabetes in dogs usually has nothing to do with their diet, and cats are unlikely to enjoy eating sugary treats anyway.

To understand diabetes, you need to know the basic facts about the control of blood sugar (glucose) in the body. In a healthy animal (or person), the blood glucose level is maintained at the correct level, somewhere between 3 and 8. If the glucose level goes higher than this, special cells in the pancreas produce higher levels of insulin, and this hormone causes cells around the body to take up more glucose, reducing the level in the blood. Then as the glucose level falls lower, less insulin is produced, and the glucose level rises. Up and down goes the blood glucose, as the insulin level goes down and up. It's more complicated than this, with other hormones playing a role too, but that's the basic story.

In diabetes, the blood glucose level goes up far too high, causing many signs of illness (from increased thirst to weight loss to behavioral changes). The usual mechanism of increased insulin production pushing the glucose level down again stops working. There are two different ways that this happens, and across the species, diabetes (or “diabetes mellitus” as it is correctly known) is divided into two types.

Type 1 happens when the pancreas stops producing enough insulin, due to the auto-immune destruction of the special cells in the pancreas that manufacture and release this hormone. No-one knows why the body's own immune system destroys its own cells, but it's partly an inherited issue, (more common in some dog breeds).

The problem is “not enough insulin”, and the answer is usually to replace the missing insulin by giving insulin injections. Type 1 diabetes causes around 10% of the cases seen in humans, tending to develop in childhood, unrelated to diet or body condition.

Interestingly, type 1 diabetes is common in dogs, but rare in cats.

Type 2 diabetes is the adult-onset version that is most common in humans, accounting for 90% of cases: it’s linked to obesity, lifestyle and a poor diet. Instead of reduced production of insulin, the problem is largely “insulin resistance”: the receptors on cells around the body don’t respond to insulin in the usual way. The cells are meant to take up more glucose when there are increased insulin levels, but they don’t do this, so the blood glucose keeps going up despite higher levels of insulin. Type 2 diabetes can often be helped by careful attention to body condition, exercise and diet, or with oral medication, but often insulin injections are also needed. This type of diabetes is common in cats, but rare in dogs.

So one in five hundred dogs get Type 1 diabetes and they need insulin injections.

One in a hundred cats get Type 2 diabetes, and they can sometimes be helped by a special diet, but usually, they need insulin injections as well.

It isn’t quite as black and white as this, but it’s a helpful general guide. It’s useful to remember that dogs are like the minority of human diabetic patients (type 1) while cats are like the most common human diabetic cases (Type 2).

So diet is relatively unimportant for diabetic dogs: traditionally they were thought to do better when kept on a higher fibre, high glycaemic index diet, but more recent research has begun to question the need for this. It’s still important that they have a uniform diet, day to day, so that their body gets used to processing similar amounts of nutrients, but a standard dog diet often suffices.

In contrast, for cats, as for humans, diet can be a very important part of therapy. A high-protein, low-carbohydrate diet is recommended; the equivalent of diabetic humans avoiding sugary foods. Moist food tends to be better than dry food because it’s easier to create lower carbohydrate levels. If you think about it, you need flour and fats to make biscuits, and pet kibble is a form of biscuit, so carbohydrates and oils are needed. As in humans, an altered diet can be enough to allow some cats to achieve full remission (i.e. the diabetes is “cured”). If not cured, cats on special diets can often manage with reduced levels of insulin injections.

For most pets, treatment does mean once or twice daily insulin injections for the rest of their lives, along with regular visits to the vet to check blood glucose levels. New technology may soon help, with devices that are implanted under the skin, allowing owners to measure their pets' blood glucose levels from a distance with a handheld device at home.

Scientific advances won't change the biggest challenge for owners of diabetic pets: it's costly to pay for ongoing monitoring and treatment. Diabetes is yet another good reason to get pets insured when they are young.