A self-contained metabolic analysis apparatus configured to be worn by a user, the apparatus comprising: a device body including (i) an integrated chemical sensor module comprising a colorimetric chemical sensor chip for simultaneous oxygen and carbon dioxide measurement, and (ii) an integrated flow sensor module for breath flow rate measurement, wherein the flow sensor module comprises a Venturi tube with a constriction, a first opening located at an upstream side of the constriction, a second opening located at a downstream side of the constriction, and a pressure sensor in sensory communication with the first and second openings, the flow sensor module being configured to determine breath flow rate from output signals of the pressure sensor; a disposable mask attached to the device body, permitting breathing from both the mouth and nose of the user, comprising: an exhalation port including a one-way valve located in a middle portion of the disposable mask to allow at least a portion of the user's exhaled breath to enter the Venturi tube; at least two inhalation ports each comprising a one-way valve and offset relative to the exhalation port; a mask body with a soft cushion along the edge; and a connection adaptor; wherein the disposable mask is configured to allow aseptic breathing according to which the user inhales ambient air through the at least two inhalation ports and exhales breath through the exhalation port into the flow sensor module, from which a portion of the user's exhaled breath is taken into the chemical sensor module; headgear adapted to attach the device body to a head of the user; and a data transmission circuit configured for communication with an external electronic device. a device body including (i) an integrated chemical sensor module comprising a colorimetric chemical sensor chip for simultaneous oxygen and carbon dioxide measurement, and (ii) an integrated flow sensor module for breath flow rate measurement, wherein the flow sensor module comprises a Venturi tube with a constriction, a first opening located at an upstream side of the constriction, a second opening located at a downstream side of the constriction, and a pressure sensor in sensory communication with the first and second openings, the flow sensor module being configured to determine breath flow rate from output signals of the pressure sensor; a disposable mask attached to the device body, permitting breathing from both the mouth and nose of the user, comprising: an exhalation port including a one-way valve located in a middle portion of the disposable mask to allow at least a portion of the user's exhaled breath to enter the Venturi tube; at least two inhalation ports each comprising a one-way valve and offset relative to the exhalation port; a mask body with a soft cushion along the edge; and a connection adaptor; wherein the disposable mask is configured to allow aseptic breathing according to which the user inhales ambient air through the at least two inhalation ports and exhales breath through the exhalation port into the flow sensor module, from which a portion of the user's exhaled breath is taken into the chemical sensor module; an exhalation port including a one-way valve located in a middle portion of the disposable mask to allow at least a portion of the user's exhaled breath to enter the Venturi tube; at least two inhalation ports each comprising a one-way valve and offset relative to the exhalation port; a mask body with a soft cushion along the edge; and a connection adaptor; wherein the disposable mask is configured to allow aseptic breathing according to which the user inhales ambient air through the at least two inhalation ports and exhales breath through the exhalation port into the flow sensor module, from which a portion of the user's exhaled breath is taken into the chemical sensor module; headgear adapted to attach the device body to a head of the user; and a data transmission circuit configured for communication with an external electronic device.