A piece of kidney sits on a plate. Would you eat it? Would you offer it to your dog or cat? While most of us would recoil in horror, most pets would eat that slab of kidney with relish. If you did, it would likely be eaten with relish, as well.

Dogs and cats are predators. For millennia, they’ve survived by eating other animals. The first parts eaten by wild carnivores are typically the abdominal contents (liver, spleen, kidneys, adrenals, pancreas) because as carnivores, the highest priority is placed on eating these organs. Muscle meats are often left to scavengers, or eaten at a later time. The genetic makeup of dogs and cats is historically, in combination with other factors, based on a diet that includes organ meats. But what is the value in consuming organs, specifically glandular tissues? To answer this, it is necessary to look at both history and current science.

Much like animals, human culinary traditions worldwide have included the consumption of organs and glands as dietary staples. Up until the 1950s, foods like liver and kidney made up a regular part of the American diet. Civilizations have long prized internal organs for their health benefits, considering glands as “functional foods” that have positive effects on health. Historically glandular tissues have been revered for their rich, dense nutrient content, as the most valuable parts of animals used for food.

Writings from as early as 1600 B.C. describe the consumption of liver to treat night blindness. Other organs have been fed to sick people and animals to support healing, regeneration, and return to function. This practice has become known as glandular therapy.

Glandular therapy

Glandular therapy (GT) refers to the practice of using whole animal tissues to support or promote the healthy functioning of a body’s internal organs. Glandular tissues contain vitamins, minerals, enzymes, peptides, nucleotides, and other nutrients, specific to each organ.

GT is based on the theory of “homostimulation,” or “like supports like.” For example, an animal eating a piece of liver is taking in nutrients that closely resemble the animal’s own liver, providing the body with similar building blocks and fuel for repair. Practitioners can think of it like this: A damaged liver needs a specific and complete combination of amino acids and other materials to rebuild functional liver cells. In GT, the most complete source of materials for liver repair would be healthy liver cells. What about brain damage? A closer look at brain tissue reveals a rich source fats (phospholipids, omega-3 and other fatty acids) vital to repair and maintenance of brain tissue. Bovine trachea and cartilage contain glycosaminoglycans, important compounds (like hyaluronic acid, chondroitin sulfate) for joint health. As mentioned before, “like heals like.”

Starting in the early 1900s, scientists actively sought to break foods apart, looking for the “active principles” responsible for health benefits. Once isolated, a compound could be manufactured synthetically and concentrated at lower costs, effectively replacing GT. This led to the isolation of many “active principles” including thyroxine (1926), estrogen (1941) and cortisone (1936). Predictably, the practice of GT rapidly lost favor. By the mid-1940s, GT had largely disappeared from use in medical practice.

From 1940 to the 1980s, little was done to advance the therapeutic use or clinical research of glandular tissues. With the exception of whole thyroid extracts (Armour Thyroid and others), most other glandular therapy products disappeared. Classic double-blinded cross-over studies on GT have not been performed, and data supporting the use of glandulars is primarily based on historical use.

Oral tolerance

Recently, scientific interest in the therapeutic potential for gland and organ tissues has increased with advances in oral tolerance or oral tolerization (OT).

In terms of gland or organ therapy, OT refers to the process of feeding specific animal proteins, termed oral auto-antigens, to a patient with an autoimmune condition. When the gland or organ protein is fed to the animal and passes through the gut immune tissue, it is thought to desensitize the body’s immune response to these proteins, thus calming the body’s response to its own, similar tissue. During this process, immune cells are transformed from “attacking” or “inflammatory” cells to less reactive cells, termed “regulatory” cells. OT also stimulates the production of “regulatory cytokines” that help to moderate inflammatory responses within the body. For example, a patient with chronic colitis could be fed colonic proteins. Studies have shown that feeding these patients the same protein that matches the compromised tissue in the body stimulates immune cells to release inhibitory cytokines, substances that can suppress inflammation and the autoimmune response.

While the first work on OT occurred in the 1890s at the same time that GT was common in medical practice, OT has been shown to suppress autoimmune processes in both animals and humans. Examples include multiple sclerosis, diabetes, asthma, antigen-induced arthritis, and encephalitis. The primary area of interest for OT is in management of autoimmune conditions.

While the exact mechanism of OT is still unclear, the potential benefits are significant. OT therapy has been shown to be effective, safe, non-toxic, and may offer significant benefits in supporting the body’s response to autoimmune and inflammatory diseases.

Oral tolerance and glandular therapy

Oral tolerance and glandular therapy share a number of common threads. GT is part of historical culinary and medical tradition, and OT has been under investigation for over 100 years, with significant recent findings. Both systems use glands, or substances isolated from glands, to support positive changes in compromised organs. Both operate on the “like supports like” premise. Neither has a clear understanding of their mechanisms of action. However, both OT and GT provide food-based nutrients that potentially affect overall optimal organ function.

Based on the recent advances and the clinical results in oral tolerance, coupled with the historical use of glandular tissues, there are compelling reasons for veterinarians to reconsider the value of glandular therapies. Given that veterinarians have seen a significant increase in the number and severity of autoimmune and inflammatory diseases over the past several decades, it brings the question back to the evolution of the dog and cat’s diet and the need for these animals to consume glandular tissues in some fashion.

Today, most pet foods do not include glandular tissues as ingredients – the animal tissue in these foods is mostly muscle meat. The removal of this traditional food group may be contributing to the growing number of chronic health conditions seen in pets today. Many recipes for home cooked pet diets now include glandular tissues (liver, kidney, spleen) in an attempt to create a more ancestral diet. Advances in oral tolerance coupled with renewed interest in glandular therapy fit together well in the growing use of food as medicine.