The goal of this clinical trial is to learn if changing cysteine levels in the diet can influence how the body processes cysteine in Black and White individuals aged 45-75 with a history of non-cancerous polyps. The main questions it aims to answer are: * At the beginning of the study, do Black participants have higher levels of cortisol (a stress hormone) and compounds made from cysteine in their blood when compared to White participants? * Does eating less cysteine lower the body's natural cysteine activity and lead to less gut bacteria that break down cysteine? * Does eating less cysteine lead to less inflammation in the gut and lower levels of markers of inflammation in the blood? Research will compare a high cysteine diet and a low cysteine diet, and each participant will eat both diets. Participants will be in the study for 11 weeks and 2 days. Over the course of the study, participants will: * Eat a high cysteine diet for 3 weeks, and a low cysteine diet for 3 weeks * Eat a moderate cysteine diet for 1 week before each study diet * Complete surveys * Provide blood, stool, and saliva samples * Maintain food logs