468 JOURNAL OF FOOD SCIENCE—Vol. 67, Nr. 2, 2002 © 2002 Institute of Food Technologists Concise Reviews in Food Science JFS: Concise Reviews in Food Science The Effect of Microgravity and Space Flight on the Chemical Senses A.A. OLABI, H.T. LAWLESS, J.B. HUNTER, D.A. LEVITSKY, AND B.P. HALPERN ABSTRACT: The effect of space flight and microgravity on the chemical senses is reviewed. Skylab-4 and Soyuz 30- 31 studies revealed changes in taste thresholds while no effect was found in a Canadian investigation (41-G) and conflicting results were obtained on another Soyuz mission. Two simulated microgravity studies found no effect on taste or smell sensitivity; while 5 other studies found an effect. Microgravity induces physiological changes including an upward shift of body fluids toward the head, which may lead to an attenuation of the olfactory component in the flavor of foods. Chemosensory changes may also relate to space sickness, Shuttle atmosphere, stress, radiation, and psychological factors. Keywords: microgravity, space flight, taste, smell, chemosensory INTRODUCTION F LYING IN SPACE HAS BEEN A CHAL- lenging dream for human beings all over the world. Presently, being in space has become a routine type of task for a certain privileged group of the population called astronauts or cosmo- nauts. Although the fascination with be- ing in space may fill the astronauts with a sense of fulfillment, many other phys- iological and psychological effects come into play. The physiological ef- fects are quite varied in nature and in- clude changes in energy requirements, body composition, fluid homeostasis, protein utilization, calcium/bone me- tabolism and hematopoiesis (Lane and Smith 1999). Physiological adaptation to microgravity can result in loss of red blood cells, bone loss, and changes in gastrointestinal motility (Smith and oth- ers 1997). Other aspects of the space environment can lead to alterations in the chemosensory perception of foods; these include diet, illness, and biochem- ical shifts. Of special interest to sensory analysts is the effect of microgravity on the chemical senses. This area has been clearly under-researched in space mis- sions, probably due to its lack of per- ceived terrestrial benefit. The scant lit- erature that exists about chemosensory research under conditions of micro- gravity is sometimes contradictory and leaves a window for speculation. Subjective reports from both Soviet and American astronauts report some attenuation of taste acuity (Rambaut and others 1977) and perception of an unpleasant taste in the mouth (Baranski and others 1983). A Russian study on the change in taste perception of astro- nauts in flight against the background of fatigue (Popov 1981) recommended adding different spices and condiments to food products to improve appetite under such conditions. On a similar note, a Russian cosmonaut on Vostok VI reported a reduced appetite for sweets and a desire for pungent food flavors (Oberg 1981). The physiological changes associated with microgravity and the chemical senses are not stated explicitly in the lit- erature, but if one tries to relate ob- served physiological changes to the chemical senses, some conclusions can be drawn. From a physiological point of view, the most characteristic feature of space flight is the experience of micro- gravity, which causes a shift of body flu- ids from the lower part of the body to the upper part. This fact has been well documented by a decreased leg volume (Leach and others 1996) and a facial puffiness (Figure 1) or edema of space crewmembers (Nicogossian and Parker 1982). These changes are substantial, leading to a reduction of leg volume by 1 L per leg within 6 to 10 h of reaching orbit (Leach and others 1996). Follow- ing this is a decrease in plasma volume and thirst. Also relevant to the chemosensory organs is congestion of the nasal pas- sages (Glendinning, personal communi- cation), which results in decreased air- flow, due to the engorgement of the non-olfactory mucosa, and a reduction Figure 1—Facial edema, puffiness during flight as a result of microgravity: be- fore flight (right), during flight (left) (Thornton and others 1977)