An apparatus for tracking caloric consumption and caloric expenditure of an individual, comprising: a sensor device (10, 700, 1201) adapted to be worn on an individual's body, the sensor device having at least two sensors (12, 705, 710) adapted to generate data when in proximity to said individual's body, at least a first of said sensors being a physiological sensor adapted to generate data indicative of a first parameter of said individual, the first parameter being physiological, and at least a second of said sensors adapted to generate data indicative of a second parameter of said individual; and an I/O device in electronic communication with said sensor device (10, 700, 1201); wherein said sensor device includes a processor (20, 490, 900) in electronic communication with said at least two sensors (12, 705, 710) and said I/O device, said processor (20, 490, 900) being programmed to use said data of a first parameter and a second parameter to derive caloric expenditure data of said individual, said derivation based on an algorithm, said I/O device adapted to enable said individual to enter information relating to calories consumed by said individual, said I/O device comprising a display for displaying information, said information being based on said derived caloric expenditure data and caloric consumption data generated using entered information relating to calories consumed by said individual, characterised in that: said algorithm includes: a context detector which utilises data generated by said sensors (12, 705, 710) and demographic information for the individual to produce a weight expressing a probability that a given portion of said data was generated by said sensors (12, 705, 710) while the user was in each of several possible user activity contexts, a regression algorithm for each user activity context, each regression algorithm producing an output that is an estimate of caloric expenditure for its respective user activity context, and a post processor which combines the weights and the regression algorithm outputs, and outputs the caloric expenditure. a sensor device (10, 700, 1201) adapted to be worn on an individual's body, the sensor device having at least two sensors (12, 705, 710) adapted to generate data when in proximity to said individual's body, at least a first of said sensors being a physiological sensor adapted to generate data indicative of a first parameter of said individual, the first parameter being physiological, and at least a second of said sensors adapted to generate data indicative of a second parameter of said individual; and an I/O device in electronic communication with said sensor device (10, 700, 1201); wherein said sensor device includes a processor (20, 490, 900) in electronic communication with said at least two sensors (12, 705, 710) and said I/O device, said processor (20, 490, 900) being programmed to use said data of a first parameter and a second parameter to derive caloric expenditure data of said individual, said derivation based on an algorithm, said I/O device adapted to enable said individual to enter information relating to calories consumed by said individual, said I/O device comprising a display for displaying information, said information being based on said derived caloric expenditure data and caloric consumption data generated using entered information relating to calories consumed by said individual, characterised in that: said algorithm includes: a context detector which utilises data generated by said sensors (12, 705, 710) and demographic information for the individual to produce a weight expressing a probability that a given portion of said data was generated by said sensors (12, 705, 710) while the user was in each of several possible user activity contexts, a regression algorithm for each user activity context, each regression algorithm producing an output that is an estimate of caloric expenditure for its respective user activity context, and a post processor which combines the weights and the regression algorithm outputs, and outputs the caloric expenditure. said algorithm includes: a context detector which utilises data generated by said sensors (12, 705, 710) and demographic information for the individual to produce a weight expressing a probability that a given portion of said data was generated by said sensors (12, 705, 710) while the user was in each of several possible user activity contexts, a regression algorithm for each user activity context, each regression algorithm producing an output that is an estimate of caloric expenditure for its respective user activity context, and a post processor which combines the weights and the regression algorithm outputs, and outputs the caloric expenditure. a context detector which utilises data generated by said sensors (12, 705, 710) and demographic information for the individual to produce a weight expressing a probability that a given portion of said data was generated by said sensors (12, 705, 710) while the user was in each of several possible user activity contexts, a regression algorithm for each user activity context, each regression algorithm producing an output that is an estimate of caloric expenditure for its respective user activity context, and a post processor which combines the weights and the regression algorithm outputs, and outputs the caloric expenditure.