Glycine is a conditionally essential amino acid that plays many important roles in the body, including the support of healthy digestion. When there are adequate amounts of the precursors, serine, threonine, and/or choline available, humans can synthesize the necessary levels of glycine required. However, in conditions where there is more glycine required than can be synthesized and/or there is low dietary intake, then there may be insufficient glycine levels to perform key digestive functions. These include the synthesis of glutathione and structural proteins, including collagen, heme, creatine, nucleic acids, uric acid, and bile salts.
Another role of glycine is to modulate intracellular calcium levels, which impacts immune function, superoxide production, and cytokine synthesis. Glycine also acts as a neurotransmitter, controlling food intake, behavior, and homeostasis. As such, glycine contributes to metabolism, growth, development, immunity, and cryoprotection. Chronic suboptimal levels of glycine may contribute to problems, including impaired immune responses and nutrient metabolism. Among its many roles, glycine also impacts digestion in two key ways: fat digestion and redox balance.
Glycine plays an important role in fat digestion because of bile. After the synthesis of bile acids in the liver, bile salts conjugate to either glycine or taurine to increase solubility. Then the bile salts are secreted into bile and stored in the gallbladder to be ready for release to aid in the digestion of dietary fats upon ingestion and as fat-soluble vitamins. Alterations in bile salts may lead to fat malabsorption and deficiencies in the fat-soluble vitamins, contributing to digestive disorders and malnutrition.
Glutathione plays a vital role in maintaining redox balance in the body to reduce the risk of damage from excess oxidative stress and associated inflammation. These properties additionally support a healthy digestive system. Many digestive disorders are associated with oxidative stress and inflammation, including inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), and celiac disease.
Research illustrates that the reductions in glutathione correlate with oxidative stress. Glycine supplementation can restore glutathione levels to support redox balance. Studies have also found that glycine supplementation supports digestive disorders through its influence on glutathione.
In one study on experimentally induced colitis, glycine supported the epithelial antioxidant defenses. This protected the intestinal epithelial cells from damage. The researchers proposed that the glycine-specific transporter, GLYT1, in the intestines allows for targeted glycine uptake to respond directly to oxidative challenges and protect them from potential damage.
Rat studies have also found that glycine supplementation protects the gastrointestinal tract from oxidative damage from acid and/or pepsin, and from nonsteroidal anti-inflammatory drug (NSAID) damage. One such study was conducted on a model of reflux esophagitis.
Most diets with adequate protein intake provide sufficient levels of glycine and/or its precursors to support a normal glutathione status and bile flow. However, in some conditions of disease and/or with inadequate intake, additional glycine support may help an individual reach adequate levels of glycine to support healthy digestion* and other body processes that require glycine.
By Kendra Whitmire