An automated system for controlling a patient's blood glucose, including a blood glucose sensor, a device for measuring a physical activity of the patient, and a processing and control unit, wherein: the processing and control unit is configured to generate, by convolution of a signal PA supplied by the device for measuring a physical activity of the patient with a decreasing mathematical function H, a signal IPA representative of the influence of the patient's physical activity on his/her insulin sensitivity; and the processing and control unit is configured to calculate, from a first patient-specific mathematical model fCR and taking into account signal IPA and from a single blood glucose value Gr measured by the sensor, a factor CR representative of the patient's insulin sensitivity.