According to an aspect, there is provided a method of monitoring a subject to identify when the subject has eaten food, the method comprising obtaining measurements of the heart rate variability, HRV, of the subject over a first time interval； obtaining measurements of one or both of physical activity of the subject over the first time interval and measurements of a level of carbon dioxide in the environment of the subject over the first time interval； processing the HRV measurements and said one or both of the physical activity measurements and carbon dioxide, CO2, measurements to identify periods of time in which the subject has eaten food； and generating a signal indicative of the identified periods of time in which the subject has eaten food.
