Oral N-acetylglucosamine in Crohn's Disease

While many new medications improved care for patients with Crohn's disease, clinical remission is only achieved in \~40% of patients - a therapeutic ceiling that has not changed in 20 years. These data underscore the need for new treatment strategies and (the investigators hypothesize) greater focus on personalized medicine using factors like genetics. This study is a clinical trial of oral N-acetylglucosamine (GlcNAc) in patients with Crohn's disease. The investigators are aiming for approximately half of the participants to carry a genetic variant in a gene called ZIP8. ZIP8 regulates levels of manganese and the variant lowers levels of manganese; manganese levels may also be reduced for reasons other than just ZIP8 genetics - including variation in dietary intake, water sources, and inflammation - therefore, the investigators are also enrolling participants who do not have the ZIP8 variant. Manganese is a nutrient absorbed from food that is required for glycosylation, but direct supplementation of excess manganese may carry risk of neurologic side effects. An alternative approach is to supplement with GlcNAc, the critical building block of glycosylation that regulates intestinal health and inflammation. GlcNAc is preferred given its positive safety profile and prior small studies in patients with inflammatory bowel disease that showed promising results. Key study information: * The investigators will check if the participant carries the ZIP8 variant at study enrollment. The participants can choose to be informed of ZIP8 genetics. * This is a randomized, double-blind, placebo-controlled, cross-over study. This study design provides the most power to determine if there is a beneficial effect of GlcNAc. * This means the participant will receive the study drug (GlcNAc), but will also have a period of placebo. The sequence in which the participant receives the GlcNAc or placebo is randomized. The study is blinded, meaning that the participant and the investigator will not know if the participant is receiving active drug or placebo unless there are safety concerns. * GlcNAc or placebo is provided to the participant as a powder that the participant will mix in a small amount of water 3 times per day. * GlcNAc is a naturally-occurring substance found in nature and tastes sweet when mixed with water. * The study runs for 18 weeks. There are brief, weekly check-ins and 7-8 in-person visits. * Participants will be asked to provide blood, stool, and saliva samples for a total of 7-8 times. * If it is possible at the participant's site, intestinal ultrasounds will be performed over the course of the study. * Participants will be paid to participate in the study. There are no direct costs to the participants.