Glutamine is an important nitrogen donor in intracellular metabolism and is used in the body for repair of skin, hair, gastrointestinal tissue, muscles, hormones and much more.
Like all nutritional deficiencies, when a body is low in adequate amounts of glutamine or catabolic state, the physiological demands are increased to distribute reserves to tissue in need of glutamine.
In conditions of cancer, often many vitamins, minerals and overall nutrition are deficient.  It could be argued that this is due to lack of appetite in times of cancer or tumors consuming more to feed growth, but the foundation still remains that the body is commonly deficient.

Is Glutamine Safe to Take in Cancer?

When attempting to research information on the internet around herbal medicine, nutrition and particularly glutamine, we may find repeated pages telling us that "glutamine feeds cancer and should not be taken."
But is this true?
According to a paper by Anderson and Lalla (2020) both people with and without cancer tumors have high plasma levels of glutamine. Furthermore glutamine, as stated previously, is essential for most tissue repair and optimal function.
For this reason it is better to focus on holistic health and avoid theoretical risk. The beneficial effects of glutamine in the repair of damaged tissue and increased demands of the cancerous body are more imporant in the best recovery from disease.

Conventional Chemotherapy and Radiotherapy Effects

Patients undergoing conventional cancer treatment experience many side effects such as-

• hair loss due to damage of the follicle
• Skin damage/sores to damage of the epithelium cells
• Gastrointestinal tract irritation - eg mouth sores, stomach discomfort, oesophagus burning, etc
• Bone marrow pressure - white blood cell production
• Cardiovascular inflammation 

How Can Glutamine Help in Cancer Treatment?

Human clinical trials of glutamine use in cancer treatment have shown the following positive effects-

• Reduces mucosal inflammation in Radiotherapy
• reduces stress response and cortisol response
• reduces inflammation in chemotherapy
• promotes immune recovery after chemotherapy
• Reduces peripheral neuropathy 
• Prevents inflammation in the oesophagus
• Prevents Radiotherapy-induced dermatitis
• Reduces intestinal gut permeability in Chemotherapy
• Reduces diarrhoea in radiotherapy
• Reduces oedema in chemotherapy

Amara, S. (2008, October). Oral glutamine for the prevention of chemotherapy-induced peripheral neuropathy. Annals of Pharmacotherapy. Ann Pharmacother. https://doi.org/10.1345/aph.1L179

Anderson, P. M., & Lalla, R. V. (2020, June 1). Glutamine for amelioration of radiation and chemotherapy associated mucositis during cancer therapy. Nutrients. MDPI AG. https://doi.org/10.3390/nu12061675

Anderson, P. M., Schroeder, G., & Skubitz, K. M. (1998). Oral glutamine reduces the duration and severity of stomatitis after cytotoxic cancer chemotherapy. Cancer, 83(7), 1433–1439. https://doi.org/10.1002/(SICI)1097-0142(19981001)83:73.0.CO;2-4

Azman, M., Mohd Yunus, M. R., Sulaiman, S., & Syed Omar, S. N. (2015). Enteral glutamine supplementation in surgical patients with head and neck malignancy: A randomized controlled trial. Head and Neck, 37(12), 1799–1807. https://doi.org/10.1002/hed.23839

Cerchietti, L. C. A., Navigante, A. H., Lutteral, M. A., Castro, M. A., Kirchuk, R., Bonomi, M., … Uchima, P. (2006). Double-blinded, placebo-controlled trial on intravenous l-alanyl-l-glutamine in the incidence of oral mucositis following chemoradiotherapy in patients with head-and-neck cancer. International Journal of Radiation Oncology Biology Physics, 65(5), 1330–1337. https://doi.org/10.1016/j.ijrobp.2006.03.042

Chang, S. C., Lai, Y. C., Hung, J. C., & Chang, C. Y. (2019). Oral glutamine supplements reduce concurrent chemoradiotherapy-induced esophagitis in patients with advanced non-small cell lung cancer. Medicine, 98(8), e14463. https://doi.org/10.1097/MD.0000000000014463

Cruzat, V., Rogero, M. M., Keane, K. N., Curi, R., & Newsholme, P. (2018, November 1). Glutamine: Metabolism and immune function, supplementation and clinical translation. Nutrients. MDPI AG. https://doi.org/10.3390/nu10111564

Eda, K., Uzer, K., Murat, T., & Cenk, U. (2016). The effects of enteral glutamine on radiotherapy induced dermatitis in breast cancer. Clinical Nutrition, 35(2), 436–439. https://doi.org/10.1016/j.clnu.2015.03.009

Han, Y., Zhang, F., Wang, J., Zhu, Y., Dai, J., Bu, Y., … Sun, X. (2016). Application of Glutamine-enriched nutrition therapy in childhood acute lymphoblastic leukemia. Nutrition Journal, 15(1). https://doi.org/10.1186/s12937-016-0187-4

Holecek, M. (2013, September). Side effects of long-term glutamine supplementation. Journal of Parenteral and Enteral Nutrition. JPEN J Parenter Enteral Nutr. https://doi.org/10.1177/0148607112460682

Huang, C. J., Huang, M. Y., Fang, P. T., Chen, F., Wang, Y. T., Chen, C. H., … Lee, H. H. (2019). Randomized double-blind, placebo-controlled trial evaluating oral glutamine on radiation-induced oral mucositis and dermatitis in head and neck cancer patients. American Journal of Clinical Nutrition, 109(3), 615–625. https://doi. org/10.1093/ajcn/nqy329

Kucuktulu, E., Guner, A., Kahraman, I., Topbas, M., & Kucuktulu, U. (2013). The protective effects of glutamine on radiation-induced diarrhea. Supportive Care in Cancer, 21(4), 1071–1075. https://doi.org/10.1007/s00520-012-1627-0

Mehta, P., McAuley, D. F., Brown, M., Sanchez, E., Tattersall, R. S., & Manson, J. J. (2020). COVID-19: consider cytokine storm syndromes and immunosuppression. The Lancet, 0(0). https://doi.org/10.1016/S0140-6736(20)30628-0

Peterson, D. E., Jones, J. B., & Petit, R. G. (2007). Randomized, placebo-controlled trial of saforis for prevention and treatment of oral mucositis in breast cancer patients receiving anthracycline-based chemotherapy. Cancer, 109(2), 322–331. https://doi.org/10.1002/cncr.22384

Rotovnik Kozjek, N., Kompan, L., Žagar, T., & Mrevlje. (2017). Influence of enteral glutamine on inflammatory and hormonal response in patients with rectal cancer during preoperative radiochemotherapy. European Journal of Clinical Nutrition, 71(5), 671–673. https://doi.org/10.1038/ejcn.2017.11

Sands, S., Ladas, E. J., Kelly, K. M., Weiner, M., Lin, M., Ndao, D. H., … Bender, J. G. (2017). Glutamine for the treatment of vincristine-induced neuropathy in children and adolescents with cancer. Supportive Care in Cancer, 25(3), 701–708. https://doi.org/10.1007/s00520-016-3441-6

Tsujimoto, T., Yamamoto, Y., Wasa, M., Takenaka, Y., Nakahara, S., Takagi, T., … Ito, T. (2015). L-glutamine decreases the severity of mucositis induced by chemoradiotherapy in patients with locally advanced head and neck cancer: A double-blind, randomized, placebo-controlled trial. Oncology Reports, 33(1), 33–39. https://doi.org/10.3892/or.2014.3564

Wang, W., Lin, J., Lin, T., Chen, W., Jiang, J., Wang, H., … Chen, P. (2007). Oral Glutamine Is Effective for Preventing Oxaliplatin-Induced Neuropathy in Colorectal Cancer Patients. The Oncologist, 12(3), 312–319. https://doi.org/10.1634/theoncologist.12-3-312

Yousheng, L., Zeping, Y., Fangnan, L., Li, T., BO, W., & Jieshou, L. (2006). Oral glutamine ameliorates chemotherapy-induced changes of intestinal permeability and does not interfere with the antitumor effect of chemotherapy in patients with breast cancer: a prospective randomized trial - PubMed. Tumori Journal, 92(5), 396–401. https://pubmed.ncbi.nlm.nih.gov/17168431/