Digestion

Digestive Enzymes in Dogs: Amylase, Protease, Lipase and More

Different digestive enzymes act on different components of food. Some break down starch, others proteins or fats, while enzymes such as fructanase, xylanase, cellulase, beta-glucanase and phytase act on more complex plant-derived substrates. Understanding these different activities helps explain why digestion is a sequence of specialised chemical reactions rather than one single process.

Science explainer

Digestive Enzymes in Dogs: Amylase, Protease, Lipase and More

Content type

Science explainer

Focus

Digestive enzyme activity and breakdown of carbohydrates, proteins, fats and plant-derived substrates

The big question

Food contains many different types of molecules.

Starch is chemically different from protein. Protein is different from fat. Plant cell walls contain yet another collection of complex carbohydrates.

No single digestive enzyme can break all of these materials apart.

Instead, digestion depends on specialised enzymes, each capable of acting on particular chemical bonds or substrates.

The big question is:

What do the different digestive enzymes actually do, and why does the type of enzyme matter?

How do scientists study it?

Enzymes are biological catalysts.

They accelerate chemical reactions without being consumed by those reactions.

Digestive enzymes help break large food molecules into smaller components that can be absorbed, further digested or processed by microorganisms elsewhere in the gastrointestinal tract.

A useful way to understand them is to look at the substrate each enzyme acts upon.

Carbohydrate-active enzymes

These act on starches and more complex carbohydrate structures.

They include amylase, fructanase, cellulase, xylanase and beta-glucanase.

Protein-active enzymes

Proteases break proteins into smaller peptides and amino-acid-containing fragments.

Fat-active enzymes

Lipases act on dietary fats.

Phosphate-releasing enzymes

Phytase acts on phytate, a phosphorus-containing compound commonly found in plant material.

Different enzymes therefore contribute to different parts of the digestive process.

What can we measure?

The main enzyme activities relevant to this discussion can be considered individually.

Amylase

Amylase acts on starch.

Starch consists of long chains of glucose molecules. Amylase helps break particular bonds within those chains, producing smaller carbohydrate fragments that can be processed further.

Dogs produce pancreatic amylase naturally, and pancreatic secretions release it into the small intestine.

Protease

Protease is a broad term for enzymes that break peptide bonds within proteins.

Protein digestion begins in the stomach and continues extensively within the small intestine through pancreatic and intestinal enzyme activity.

The result is progressively smaller peptides and amino acids that can ultimately be absorbed.

Lipase

Lipase acts on dietary triglycerides.

Fat digestion depends on the interaction between bile and lipase activity.

Bile helps disperse fat into smaller droplets, increasing the surface area available to enzymes.

Pancreatic lipase can then break triglycerides into smaller lipid components that can be absorbed through the intestinal lining.

Fructanase

Fructans are carbohydrates made largely from chains of fructose.

Fructanase describes enzyme activity capable of breaking bonds within fructan molecules.

Dogs do not rely on fructans as a major direct source of glucose in the way they can digest starch. Fructans that remain intact can therefore become substrates for microbial fermentation further along the gastrointestinal tract.

Cellulase

Cellulose is a major structural component of plant cell walls.

Mammals do not produce substantial endogenous cellulase activity, so cellulose is not digested by the dog's own enzymes in the same way as starch.

Cellulase breaks bonds within cellulose molecules, producing smaller carbohydrate fragments.

Xylanase

Xylans are hemicellulose carbohydrates found within plant cell walls.

Xylanase breaks particular bonds within these structures.

Like cellulose, xylan is different from starch and requires different enzyme activity for degradation.

Beta-glucanase

Beta-glucans are glucose polymers with chemical bonds that differ from those found in starch.

Beta-glucanase acts on these beta-linked carbohydrate structures.

Beta-glucans occur naturally in cereals including barley and oats, as well as in other biological materials.

Phytase

Phytate is a storage form of phosphorus found particularly in seeds and cereal grains.

Phytase removes phosphate groups from phytate.

This can alter the chemical form in which phosphorus and associated minerals are present within a food matrix.

What have we learned?

The important point is not simply that digestive enzymes exist.

It is that enzyme activity is substrate-specific.

Amylase does not perform the same job as lipase.

Lipase cannot replace protease.

And enzymes capable of acting on complex plant carbohydrates target structures that mammalian digestive enzymes may process poorly or not at all.

This creates a much more detailed view of digestion:

Starch → amylase

Protein → proteases

Fat → lipase

Fructans → fructanase

Cellulose → cellulase

Xylans → xylanase

Beta-glucans → beta-glucanase

Phytate → phytase

Food itself is chemically diverse, so the enzymatic processes involved in breaking it down are diverse too.

Why does this matter?

Enzyme diversity helps explain why digestion should not be thought of as a single reaction.

A meal contains many different substrates, and each substrate follows a different digestive pathway.

For nutrients that can ultimately be absorbed by the dog, enzymatic breakdown is an important step before absorption.

For other dietary components, the extent of digestion earlier in the gastrointestinal tract can influence how much material remains available to microbial communities further downstream.

This links enzyme science directly to the broader Science Hub framework:

Food → Enzyme activity → Digestion → Substrate availability → Microbiome

It also explains why the presence of several different enzyme activities is scientifically more meaningful than simply referring to a product as containing “digestive enzymes”.

Each enzyme should be considered according to the substrate it acts upon.

Whether supplying additional enzyme activity produces a meaningful benefit in an individual healthy dog is a separate question and requires direct experimental evidence.

For a barley ingredient with naturally occurring enzyme activities, read our explanation of Enzyme Rich Malt Extract.

For ingredients and daily feeding information, visit the CaniNectar product page.

What should we keep in mind?

Several distinctions are important when interpreting enzyme science.

Enzyme activity does not automatically mean clinical benefit

Demonstrating that an enzyme can break down a particular substrate does not prove that adding that enzyme to a dog's diet will produce a meaningful health effect.

Dogs already produce important digestive enzymes

Healthy dogs naturally produce substantial pancreatic and intestinal enzyme activity, including enzymes involved in protein, fat and starch digestion.

Additional enzyme activity should therefore be evaluated experimentally rather than assumed to be necessary.

Not every substrate is normally digested by the dog

Complex plant carbohydrates such as cellulose and some hemicelluloses may instead pass further through the gastrointestinal tract and interact with microbial communities.

Laboratory activity and gastrointestinal activity are not identical

An enzyme may demonstrate activity under laboratory conditions, but activity within the gastrointestinal tract also depends on factors including pH, temperature, transit time, substrate availability and enzyme stability.

Enzyme source matters

Different enzyme preparations can contain different enzymes, activities and concentrations.

Results from one preparation therefore cannot automatically be transferred to another.

Sources and further reading

References

Further reading:

Hand MS, Thatcher CD, Remillard RL, Roudebush P, Novotny BJ. Small Animal Clinical Nutrition. 5th edition. Mark Morris Institute.

Wernimont SM, Radosevich J, Jackson MI, et al. The Effects of Nutrition on the Gastrointestinal Microbiome of Cats and Dogs: Impact on Health and Disease. Frontiers in Microbiology. 2020;11:1266.

Pilla R, Suchodolski JS. The Gut Microbiome of Dogs and Cats, and the Influence of Diet. Veterinary Clinics of North America: Small Animal Practice. 2021;51(3):605–621.

Twomey LN, Pethick DW, Rowe JB, et al. Effect of enzyme supplements on macronutrient digestibility by healthy adult dogs. British Journal of Nutrition.

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