1. A system for remote monitoring of food intake and physical activity of a subject, comprising: a) a device configured to be worn on the subject for remote monitoring of food intake and physical activity by the subject, comprising: a housing; a bus inside the housing; one or more physiological sensors connected to the bus; two or more imaging sensors connected to the bus and positioned in the housing to record a stereo image; an eating detector in the housing and connected to the bus, the eating detector comprising a light beam source configured in the device to pass a light beam in a path in front of the subject's mouth and a light sensor able to measure light intensity data representative of movement of an object in the path of the light beam; a microprocessor connected to the bus; a data storage device connected to the bus and comprising a data storage medium; programming instructions, stored on the data storage device, that when executed by the microprocessor cause the microprocessor to: receive the light intensity data from the light sensor; identify based on changes in the received light intensity data when the object is in the path of the light beam to determine when the subject is eating; generate a signal to control the imaging sensors to obtain images of a food item being eaten by the subject when it is determined that the subject is eating; and generate, from the images, a stereo image of the food item; and a power supply connected to the bus; b) a computer; and c) a data communication interface for transferring data between the device and the computer, wherein one or both of the device and the computer comprises one or more programs for determining a dimension of the food item based on: the stereo image of the food item, the distance between the two or more imaging sensors, and a fitting algorithm which fits a virtual template shape to the stereo image of the food item; and determining a physical activity of the subject wearing the device based on data from at least one of the physiological sensors, or the imaging sensors.