And that's why many veterinarians and pet nutrition experts are increasingly recommending digestive enzyme supplements.The role of enzymes to health is far greater than has been previously understood, says Mary L. Brennan, DVM, of Snellville, GA, in her book "The Natural Dog: A Complete Guide for Caring Owners" (Penguin, New York). " In addition to the role that enzymes play in digesting foods," she points out, "they are involved in every metabolic process, including the functions of the immune system, blood system, and the organs."

Digestive enzymes are produced in the pancreas and salivary glands and help to break down the protein, carbohydrate, and fat components of food for use by the body. As animals age, the production of these enzymes often slows down. Deficiencies can also be genetically-related and symptoms will show up among kittens and puppies.

Research shows a strong connection between deficiencies and diseases -- both acute and chronic.

Typical signs of deficiencies are voluminous stool, often with undigested fat clearly visible; animals who eat their own feces; and animals who are overtly underweight despite big appetites.

Michael Lemmon, DVM, at his Highlands Veterinary Clinic in Renton, Wash, employs many nutritional approaches in his practice and is a long-time advocate of digestive enzymes. Lemmon often refers to the pioneering research of Frances Pottenger, Jr. a California doctor who conducted a 10-year study of cats a half-century ago. Pottenger found a strong relationship between cooked meat and allergic reactions. Compared to cats fed raw meat, the animals on cooked diets developed skin problems and allergies that became progressively worse from one generation to the next.

Dogs and cats, of course, evolved on raw food, including raw meat, and not on the highly-processed, highly-cooked commercial food that is doled out to the domesticated pets of today. Raw foods contain their own built-in supply of enzymes, which facilitates the process of digestion. When food is cooked, the naturally-occurring enzymes are destroyed, causing the body to activate its own enzyme production to break down the food.

According to Dr. Edward Howell, a pioneering biochemist and researcher in enzyme nutrition, this situation robs enzymes for use in other important metabolic functions, such as helping the healing and immune systems of the body.

Many years ago, Howell talked in terms of an enzyme bank account, a reserve that we are born with but that becomes depleted by use over time. He believed that we (pets and people alike) should eat more raw food. If we didn't, than, in the interest of a longer and healthier life, enzyme supplements should be used to "spare" the reserves, he said. Otherwise, the resulting metabolic dislocations could contribute to serious disease.

" My first recommendation is to raise the level of the quality of a pet's food," says Lemmon. "That means taking the time, if possible, to provide your pet with range-fed, organically-grown raw meat."

Lemmon's recipe calls for one-third each of uncooked meat, raw vegetables (grated or chopped into smaller pieces with a food processor) and either soaked or cooked whole grains such as rolled oats.

If you do introduce raw food into your pet's diet, do it slowly, advises veterinarian Brennan. Too much, too quickly can create diarrhea.

Since most pet owners, for convenience sake, will opt for commercial food, veterinarians like Lemmon and Brennan recommend a high-quality supplement of digestive enzyme added to the food.

" Enzymes are a primary tool in dealing with many different problems," says Lemmon. "In some cases I will recommend enzymes alone, while in many others it is one part of a multiple remedy approach."

Improved hair coat and skin, and maintenance of good body weight are some of the typical benefits of supplementation. "If is an underweight problem, the added enzymes -- often by themselves -- will help the situation," he says.

In Lemmon's experience, the enzymes may also aid older animals suffering from joint ailments. By enhancing digestion and absorption of nutrients, including anti-oxidants and the mineral magnesium, the body is better able to counteract harmful degenerative processes.

Supplements are particularly beneficial to aging animals with slumping pancreatic enzyme production, a common condition. In his two landmark books on pet supplementation ("How to Have a Healthier Dog" and "The Very Healthy Cat Book," Orthomolecular Specialties, San Jose), Wendell Belfield, DVM, reports that added enzymes can often restore normal appearance and vigor in a few weeks.

The added enzymes enable animals to extract more nutrition from their food and thus better nourish bodily systems. With supplementation, many become more resistant to disease and infections.

In "Pet Allergies: Remedies For An Epidemic" (Very Healthy Enterprises, Inglewood, CA), Alfred Plechner, DVM, recommends routine testing of patients for enzyme deficiencies. In his practice, he finds moderate deficiencies in about a quarter of all cases, even in young animals. Because many deficiencies are not severe, the resulting problems are often attributed to other causes. Even a small deficiency, he says, can create allergic problems.

Anitra Frazier, the author of "The New Natural Cat Book" (Plume, New York), recommends digestive enzymes, among other supplements, as an aid in dealing with stress, allergies, arthritis, feline infectious peritonitis, liver, kidney and other common problems.

Supplements contain fractions or component enzymes that break down different kinds of food. Protease is the enzyme that breaks down protein. Amylase works on carbohydrate and lipase is the fat-breaking enzyme. Veterinarians advise that it is important to use supplements with a balanced formula of enzymes.

Howell, the enzyme pioneer, developed supplements derived from aspergillis oryzae (a fungus) after finding them to be more effective than animal-based pancreatic supplements. Subsequent research has confirmed his original conclusions.

A comprehensive article on digestive enzymes in the August 1993 issue of The Townsend Letter For Doctors, cited the following scientific findings:

Aspergillis enzymes possess unusually high stability and activity under a wide range of pH conditions, distinguishing them from animal enzymes (i.e., pepsin, pancreatin, trypsin, chymotrypsin, pancrelipase, and pancreatic amylase), which require pH conditions often lacking when impaired health is involved.

Protease from aspergillis, absorbed into the bloodstream, may be able to hydrolyze (break down) dietary proteins and polypeptides which have leaked into the bloodstream as food antigens. Such substances absorbed intact from the gut can cause disturbances in the body.

Human and animal studies find lipase from aspergillis effective in the treatment of malabsorption and steatorrhea (excess amounts of fat in the feces, as a result of malabsorption) due to pancreatic enzyme insufficiency.

Studies show that gastric acidity destroys up to 90% of the lipase content of exposed pancreatin given in powder, capsule or tablet form. This necessitates large dosages and greater expense for efficacy. Aspergillis lipase, by comparison, is resistant to inactivation by gastric acidity.

A 1988 study in England with dogs found that a small dose (400 mg) of aspergillis lipase was as effective as conventional pancreatin 25 times larger (10,000 mg) in the treatment of malabsorption, malnutrition and steatorrhea due to pancreatic insufficiency.