"All NASA astronauts aboard the International Space Station undergo routine medical evaluations, have dedicated flight surgeons monitoring them, and are in good health."

The cold environment of space further increases the body's energy demands, leaving astronauts like Williams and Wilmore at risk of nutritional deficiencies. Dr. Gupta suspects Williams’s body may be burning more energy as it adapts to weightlessness and maintains warmth in the harsh space environment.

Astronaut Sunita Williams, along with her colleagues Butch Wilmore, Nick Hague and Don Pettit, cast their votes for the U.S. election from the International Space Station. On Tuesday, Hague shared an Instagram post showing the group in patriotic socks,

NASA is facing rising concerns about the health of astronauts Sunita Williams and Barry Butch Wilmore, who have been held up on the International Spac

Soon after Sunita Williams' “gaunt” transformation led doctors to raise health alarms, NASA reiterated the safety of those on board the ISS.

Although Williams and Wilmore have maintained a positive public image, a recent photo suggests otherwise, according to Dr. Vinay Gupta, a pulmonologist and expert from Seattle. Dr. Gupta told DailyMail.com, “The picture shows someone who is likely experiencing the stresses of extended stays at high altitudes, even in a pressurized cabin.”