The stranded NASA astronaut at the center of growing health fears has finally broken her silence in a video recorded from space.

Health experts and NASA insiders had raised concerns that Sunita Williams, 59, was rapidly losing weight after photos appeared to show her looking 'gaunt' earlier this month, after spending over 150 days stuck on the International Space Station. 

But Williams hit back at the 'rumors' in a live video published by NASA today, claiming that she has actually put on muscle. 

'My thighs are a little bit bigger, my butt is a little bit bigger. We do a lot of squats,' she said.

She added that she is the same weight as when she launched to the ISS in June, and bizarrely claimed the apparent change in her appearance was due to 'fluid shift.'

'I think things shift around quite a bit, you probably heard of a fluid shift,' Williams said.

'Folks in space you know, their heads look a little bit bigger because the fluid evens out along the body.'

During spaceflight, weightlessness instantly shifts blood and fluids from the lower portion of the body to the upper areas, which can sometimes result in a puffy pace and thinner legs.

Williams and her crewmate Barry Wilmore, 61, have been living on the ISS for five months after Boeing's faulty Starliner spacecraft was deemed unsafe to return them to Earth.

The mission was initially only supposed to be eight days but the astronauts won't return until February 2025. 

Williams spoke with the New England Sports Network Clubhouse Kids Show Tuesday while more than 250 miles above Earth's surface. 

During the interview, she addressed health concerns, calling them 'rumors,' and discussed her food intake, such as dining on a Turkish fish stew with olives and rice.

Williams did not provide details about her caloric intake while aboard the ISS.

A photo taken September 24 initially sparked health fears. A doctor told DailyMail.com at the time her cheeks looked 'sunken', possibly as a result of rapid weight loss.

Dr Vinay Gupta, a pulmonologist and veteran in Seattle, told DailyMail.com at the time that although she did not seem at a place where her life was in danger, 'I don't think you can look at that photo and say she has sort of healthy body weight.' 

More recently, a NASA source told the New York Post that NASA has been scrambling to 'stabilize the weight loss and hopefully reverse it.'

The unnamed employee who is 'directly involved with the mission' said that Williams has been 'unable to keep up with the high-caloric diets that astronauts must consume' while on the ISS. 

'The pounds have melted off her and she's now skin and bones. So it's a priority to help her stabilize the weight loss and hopefully reverse it,' the NASA source told the New York Post.

Williams and Wilmore still have to wait about three to four months until they can return to Earth on SpaceX's Crew Dragon.

At this time, there is no evidence to suggest that Williams' alleged health decline will impact this timeline.

But the female body suffers more in space than their male counterparts.

A study assembled by NASA in 2014 found that women have greater loss of blood plasma volume than men during spaceflight, and women’s stress response characteristically includes a heart rate increase while men respond with an increase in vascular resistance.

The loss of blood plasma causes your metabolic rate to temporarily increase while your body mobilizes resources to adjust to the loss of plasma.

And this response can slightly elevate your calorie burn, resulting in weight loss similar to what Williams may be experiencing.

Another study released by Ball University in 2023 also found that women lose more muscle than men in a microgravity environment such as spaceflight.

'The amount of oxygen in the air is lower than it is at baseline, their nutritional intake is not going to be as robust as can be on the ground,' said Dr Gupta.

'Their ability to work out is going to be limited. So every every sort of physiologic variable that defines our well being is going to be suboptimal, especially even in a pressurized cabin, but in, you know, in outer space in their case, right?

'So what you're seeing there in that picture, especially with Sunita, is somebody that I think is experiencing the natural stresses of living at very high altitude, even in a pressurized cabin, for extended periods.'