Diabetes
mellitus (DM) is a chronic endocrine disorder characterised by
an imbalance in the metabolism of carbohydrate, fat and protein.
It is the clinical manifestation of an absolute or relative lack
of insulin. The condition may arise in response to one or more
of the following factors:
• Target tissue insensitivity
• Insulin production failure
• Insulin transport failure
DM should not, therefore, be considered a single disease with
a single cause, but rather, a heterogeneous group of disorders
characterised by hyperglycaemia.
In affected animals, insulin deficiency allows glucagon-driven
gluconeogenesis by the liver to proceed uncontrolled. This increase
in glucose production is exacerbated by reduced insulin-dependent
uptake of glucose from the circulation resulting in hyperglycaemia
and the clinical state of uncomplicated DM.
As the supply of glucose for fuel is compromised, alternative
energy substrates, such as ketones, are generated in the liver
from mobilised lipid stores, a pathway enhanced by the altered
insulin to glucagon ratio. The principal ketones are acetoacetic
acid, acetone and b -hydroxybutyrate. While of short-term benefit
for energy supply, insulin deficiency decreases utilisation of
ketone bodies by peripheral cells. As ketones continue to be produced
and then accumulate in the blood, the body’s buffering system
becomes overwhelmed culminating in the clinical state of complicated
DM or diabetic ketoacidosis.
Together with the correction of any underlying predisposing factors,
successful long-term management of DM involves a combination of
appropriate insulin replacement therapy and a suitable dietary
regimen. The goals of therapy include achieving acceptable glycaemic
control, minimising the severity of the clinical signs and maintaining
ideal body weight whilst avoiding ketoacidosis. Since DM disturbs
macronutrient metabolism, diet has a key role to play in its management.
The objectives of the dietary management of diabetic dogs are
to provide adequate nutrients for:
achieving and maintaining ideal body weight and condition
optimisation
of conditions for achieving reasonable glycaemic control
management
of concurrent diseases or complications of DM
The
presence of concurrent illnesses or complications such as pancreatitis,
cardiac disease, renal disease, hepatic disease and maldigestion/malabsorption
states have dietary priority over DM. Daily caloric intake, consistency
of the ration and coordination to insulin activity remain, however,
important.
Ideal Body Weight and Condition Dogs with Normal Bodyweight
Generally the daily caloric needs of a well-controlled diabetic
dog are similar to those of a normal healthy dog. Initially daily
caloric requirements are calculated as for maintenance but further
adjustments to maintain steady body weight and condition may be
required because of individual differences in caloric needs and
degree of glycaemic control achieved with exogenous insulin. Excess
calories should be avoided because of resultant weight gain and
potential exacerbation of the diabetic state. In addition, although
obesity is most commonly associated with difficulties in diabetic
management, underfeeding and malnutrition also have detrimental
effects on glucose metabolism. Eventual caloric intake may therefore
vary from 80 to 150 % of estimated intake for maintenance of ideal
body weight and condition. Overweight Dogs
Obesity is known to enhance down-regulation of insulin receptors,
to decrease insulin receptor binding affinity and to cause post
receptor defects in glucose metabolism, and is therefore a potential
cause and contributor to DM. Weight loss is associated with improved
glycaemic control and decreased exogenous insulin requirements.
Weight loss should be gradual and follow recommended guidelines.
Maintenance energy requirements should be introduced once the
animal achieves optimal body weight and condition. Underweight Dogs
If the dog is underweight, the diet should be fed at a maintenance
level based on the estimated ideal body weight and condition.
Short term feeding of an energy dense ration may hasten weight
gain in severely affected individuals. As with correction of obesity,
the underweight dog should be monitored regularly and maintenance
rations introduced once ideal body weight and condition are met.
Standardisation of Regimen
Optimal conditions for achieving reasonable good glycaemic control
include the maintenance of a dietary intake that is, from day
to day, consistent in its nutrient and energy composition and
its volume. And a feeding schedule that is coordinated with the
physiological effects of the administered insulin. Recommendations
vary with the type of insulin used. The most commonly used protocol
is to administer lente insulin once daily. The food is divided
into two equal portions and fed at the time of the insulin injection
and again 6 to 8 hours later. For other insulin regimens, a serial
blood glucose curve will assist in determining optimal feeding
proportions and intervals.
The exercise routine, which may alter the animal’s energy
requirements, should also be carefully regulated. In aspects of
management, a schedule should be established that is compatible
with the normal household routine.
Nutrient Manipulation
Traditionally low carbohydrate, high fat diets were recommended
for human diabetic patients, based on the premise that since diabetic
patients cannot regulate blood sugar concentrations adequately,
dietary sugar should be restricted. Fat was considered a useful
alternative energy nutrient but unfortunately in the long-term
can manifest in clinical complications such as ketoacidosis, pancreatitis
and hepatic lipidosis. Recommendations are now very different
and involve manipulation of the proportion and physical form of
the energy-giving nutrients. Carbohydrate metabolism, in particular,
is chronically disrupted in diabetes and contemporary therapy
aims to harness appropriate carbohydrate sources.
Current recommendations for the dietary management of DM in the
dog are to provide a palatable diet of consistent nutrient profile,
which should be:
High in complex carbohydrates (starch and dietary fibre)
Devoid
of simple sugars
Restricted
in fat
Moderate
in protein
Carbohydrates
Carbohydrate, the preferential substrate for mammalian energy
production, is the primary component of such a regimen and heavily
influences the overall profile of the diet. Diabetics experience
considerable difficulty regulating blood sugar levels and even
with appropriate insulin therapy, there may be wide fluctuations
in diurnal blood glucose concentrations, making delivery to metabolising
tissue erratic. Using appropriate dietary carbohydrate, the gut
can act as a reservoir, slowly releasing sugar into the blood
over an extended period. If correctly managed, this effect can
complement the action of exogenous insulin.
Simple sugars (e.g. glucose, sucrose and lactose) are cleared
relatively rapidly from the small intestine and may give rise
to rapid excursions in blood sugar levels. It is for this reason
that they are generally contraindicated for diabetics, although
this property makes them useful in combating hypoglycaemic attacks.
Starches, on the other hand, pose a considerable challenge to
the digestive capacity of the small intestine. Digestion is, therefore,
relatively slow resulting in a more gradual release of glucose
into the circulation over a period of several hours.
Certain forms of dietary fibre, which is indigestible in the mammalian
intestine, may be beneficial to diabetics. Dietary fibre slows
down the rate of digestion in the lumen of the small intestine,
and thereby slows the rate of post-prandial nutrient uptake. This
effect synergises with the slow digestion of starch, thus optimising
the ‘slow release’ of sugar from the gut lumen into
the circulation. This helps to reduce post-prandial glycaemic
peaks and improves glycaemic control in canine diabetics.
Some forms of ‘soluble’ fibre become viscous when
hydrated, and it is this type of fibre which is often quoted as
being particularly beneficial to diabetic patients. Guar has been
shown to reduce post-prandial increases in plasma glucose and
insulin concentrations in both normal and diabetic subjects. Guar
has also been shown to lower plasma cholesterol in diabetic, normal
and hyperlipidaemic humans, an effect is thought to be mediated
through interaction with bile acid circulation since fat absorption
is not directly affected.
Insoluble and non-viscous fibres have also been associated with
significant improvements in both mean blood glucose levels and
24 hour profiles. It has been shown that 20g wheat bran sprinkled
daily on the diet of both normal and diabetic dogs reduced hyperglycaemia
for at least 4 hours after feeding, although the effect was less
pronounced than that of guar.
Diets for the management of DM should, therefore, be high in complex
carbohydrates (starch and fibre) and devoid of simple sugars.
To gain optimal effects from dietary fibre it seems best to provide
a blend of both viscous and insoluble sources.
Fat
In the dog, the only requirement for dietary fat is as a provider
of essential fatty acids and as a delivery route for fat soluble
vitamins. Fat does improve palatability, particularly for dogs,
but in the human field, diabetics show a tendency to develop hyperlipidaemia
and other lipid-related complications after consuming high fat
diets. In the light of this knowledge, and without contradictory
evidence from dog studies, restriction of dietary fat is recommended.
Minerals
and Vitamins
Reduction in bioavailability of some vitamins and minerals may
be associated with elevated dietary fibre. Vitamin and mineral
levels should, therefore, be adequate to compensate for potential
deficits.
