Objective To analyze the application value of medium-chain triglyceride MCT based ketogenic diet in breast cancer patients receiving chemotherapy for more than 3 months. Method A total of 120 patients with breast cancer receiving chemotherapy intervention for more than 3 months were enrolled in the Oncology Department of Wuhan Third Hospital from March 2021 to March 2023 and were simply randomly divided into control group n = 60 and intervention group n = 60 . Among them the control group received traditional chemotherapy diet intervention and the intervention group received MCT-based ketogenic diet intervention. Both groups were subjected to clinical observation for 5 weeks. Blood ketone blood glucose and body weight of the two groups were compared before intervention after 1 2 3 and 5 weeks of intervention. Meanwhile the inflammatory indexes CRP TNF - α interleukin- 1β immune indexes CD3 + CD4 + CD8 + and the dominant bacteria group of intestinal hilum Firmicutes Bacteroidetes and Morphomycetes were compared between the two groups. The incidence of variant bacteria adverse reactions nausea vomiting diarrhea constipation and hypoglycemia were different. Result After 1 to 5 weeks of intervention blood ketone levels in the intervention group were higher than before intervention. Moreover the blood ketone in the intervention group was higher than that in the control group 1. 84±0. 12 mmol / L vs 0. 41±0. 10 mmol / L 2. 10±0. 11 mmol / L vs 0. 42±0. 09 mmol / L 2. 01±0. 15 mmol / L vs 0. 44±0. 10 mmol / L 2. 00±0. 19 mmol / L vs 0. 43±0. 08 mmol / L P<0. 05 . After 1 to 5 weeks of intervention the blood glucose level in the intervention group was higher than before intervention and the blood glucose level in the intervention group was lower than that in the control group P<0. 05 . After 5 weeks of intervention body weight decreased in both groups compared with before intervention P<0. 05 . After intervention CD3 + and CD4 + in the intervention group were higher than those in the control group 70. 15 ± 6. 07 mmol / L vs 57. 62 ± 5. 09 % and 54. 02 ± 5. 62 % vs 43. 06 ± 4. 98 % . CD8 + 30. 62±3. 45 % vs 35. 62±3. 11 % and inflammation index were lower than control group P<0. 05 . After the intervention the abundances of Firmicutes and Morphomycetes in both groups decreased and Bacteroidetes increased and the abundances of Bacteroidetes in the intervention group was higher than those in the control group while those in the Firmicutes and variant Morphomycetes were lower than those in the control group P<0. 05 . The total incidence of adverse reactions in the intervention group 13. 33% 8 / 60 was significantly lower than that in the control group 31. 67% 19 / 60 P<0. 05 . Conclusion For breast cancer patients who have received chemotherapy for more than 3 months ketogenic diet intervention based on MCT can improve the overall health status of patients and reduce the side effects of chemotherapy etc. Ketogenic diet treatment of breast cancer is safe and feasible and can provide references for clinical breast cancer chemotherapy treatment and improvement of adverse reactions.