Abstract: A method and apparatus for determining caloric expenditure of a subject. The apparatus includes a heat flow sensor having an overlay and/or conductive layer for measuring the evaporative heat loss, in addition to substantially total heat loss, for the subject. The sensor also includes a structure to enhance the migration of perspiration from edges or a bottom of the sensor onto an active region of the sensor. One sensor includes electrodes to effectuate electroendosmosis such that positively biased electrodes are formed at an edge or bottom of the sensor and a negatively biased electrode is formed at a center or top of the sensor. Through electroendosmosis the perspiration is migrated from the positively biased electrodes at the edge or bottom of the sensor to the negatively biased electrode in the center or top of the sensor. Another sensor places thermocouples at edges of a sensing portion to reduce a distance that the perspiration has to migrate.