Starch - Nutrition

What is Starch?

Starches are non-structural polysaccharides composed of individual monosaccharide sugars linked in α-1,4 glycoside linkage; and are present in both plant and animals. Amylose or amylopectin are the storage forms of monosaccharide plant sugars produced by photosynthesis; glycogen is the form of starch found in animal muscle and liver tissue. Maltodextrin is a form of synthesized starch that is used in human food production. Starches that are resistant to degradation by mammalian enzymes (referred to as resistant starches) can be formed during the cooking process.

Why is it Important?

Dietary starches are readily broken down into their monosaccharide constitutes in both dogs and cats and can contribute to a rise in post-prandial blood glucose concentrations. Once absorbed, the monosaccharide sugar glucose is available for immediate use by brain and other tissues, while gluconeogenic amino acids from protein must first be converted to glucose via hepatic gluconeogenesis. Starch is not an essential dietary nutrient, but is required for production of dry pet foods.

Roles in the Body

Starch is the storage form of carbohydrate energy found in plant and animal tissues. It can be readily hydrolysed by digestive enzymes to release free monosaccharide molecules that can absorbed by both dogs and cats, though cats appear to have a more delayed response relative to dogs. Glucose absorbed from the diet can be used directly in intermediate metabolism (ATP production) or to synthesise glycogen and fatty acid. Resistant starches are not hydrolysed by pancreatic amylases and instead act like fermentable fibres in the colonic lumen.

Consequences of Starch Deficiency

Dogs:

In otherwise healthy, non-reproductive adult dogs, there are no clinical consequences of feeding a starch-free diet. Reproductive female dogs fed completely carbohydrate-free diet without adequate protein intake during late gestation can become hypoglycaemic and ketotic, and experience an increase in foetal mortality and puppy death after whelping, though no adverse effect on growth of nursing puppies was seen. Small and toy breed puppies, are prone to developing hypoglycaemia, especially during times of physiological stress and when fed lower carbohydrate or poorly digestible carbohydrate diets.

Cats:

There are no clinical signs of feeding a carbohydrate-free diet to cats at any life-stage. Adult cats and growing kittens are able to maintain blood glucose concentration through hepatic gluconeogenesis.

Toxicity

No toxicity has been associated with high intake of starch in otherwise healthy dogs and cats, though in animals with preexisting diabetes mellitus increased starch intake may contribute to post-prandial hyperglycaemia and increase insulin requirements. Maldigestion and malabsorption of dietary starches may be a feature of feline inflammatory bowel disease.

Dietary Sources

Starch is found in cereal grains, tubers, and pulses (i.e. legumes). Resistant starches can be formed during the cooking of digestible starches. Maltodextrin is not commonly found in pet foods, but can be included as a thickener in foods intended for human consumption.

Diagnosing Starch Deficiency

If low to absent carbohydrate intake with insufficient hepatic gluconeogenesis, clinical signs of hypoglycemia can occur (e.g. lethargy, depression, seizures). Blood sugar concentrations below the normal laboratory reference interval (<5 mmol/L) will be seen on serum biochemistry profiles.

References

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