The freeze-dried food diet: What Scott Kelly’s year in space can tell us about our gut

By Danielle Prieur

Growing up, you might remember trying “astronaut food” like freeze dried ice cream while on a field trip to your local science museum.

Now imagine living a whole year on a diet of freeze dried food. That’s exactly what NASA commander and astronaut Scott Kelly did, living on the International Space Station as part of Expedition 46 that launched last March.

Expedition 46 ended on Wednesday at 11:26 EST when Kelly and Russian astronaut Mikhail Kornienko landed in Kazakhstan.

At a NASA press conference Friday, Kelly revealed his first food on Earth was a banana.

He “feels pretty good” physically after a year in zero gravity, although he finds it’s easier going into space than coming back to Earth, he said.

“There’s always a certain amount of soreness and fatigue [from landing]. This time the levels of muscle fatigue and soreness were much worse,” Kelly said.

He said the two days since his return to Earth have been full of medical tests, as NASA prepares to study Kelly and his identical twin brother, astronaut Mark Kelly for another year. Researchers want to determine the impact of long stays in space on the body, such as a trip to Mars, requiring an estimated 18 months in space for the round trip.

Kelly said he’s excited about the “Twins Study,” one of the objectives of the mission.

“The genetic part of it has a lot to do with the fact my brother and my DNA is almost identical,” said Kelly. “This kind of genetic research is very new and we’ll find out a lot [including] information about my family.”


Scott Kelly returns to Earth after 340 days in space. (Video/NASA)

As one of 12 universities and 10 studies that makes up the “Twins Study,” Northwestern University researchers led by Dr. Fred Turek, a professor of neurobiology, are studying how the gastrointestinal tract of a human being is affected by a year of living at zero gravity on a freeze-dried food diet. If we had hope to send astronauts to Mars, this kind of work becomes even more crucial.

Map of research universities that are part of the Twins Study. Photo courtesy of NASA.
Map of research universities that are part of the Twins Study. Photo courtesy of NASA.

Since last March, researchers have collected stool samples from Scott, while he lived on the International Space Station, and from his  brother, Mark who was living on Earth. The goal is to determine whether zero gravity, diet, and space flight, has an effect on the human gastrointestinal tract.

As Scott and Mark share identical genetic material, Mark becomes the control subject and Scott the research subject in the study comparing flora found in Mark’s gastrointestinal tract with Scott’s during and after the mission.

Twin brothers Mark and Scott Kelly. Scott, on the right, was the brother  who lived for a year on the International Space Station. Photo courtesy of NASA.

After Northwestern researchers collect the last samples, Dr. Stefan Green, director of DNA Services at the University of Illinois at Chicago, will be collaborating with Northwestern University researchers. He said they will use two techniques to determine which bacteria are present in the two sets of samples: meta-genomics and targeted sequencing.

Researchers at Northwestern University and University of Illinois at Chicago are sequencing the DNA found in stool samples of both brothers in order to determine how the microbiota of the gut changes after a year in zero gravity. Photo courtesy of NASA.
Researchers at Northwestern University and University of Illinois at Chicago are just one team amongst twelve working on the “Twins Study.” Photo courtesy of NASA.

In the first technique, meta-genomics, all the DNA is extracted from both samples. This DNA will include any human, bacterial or pathogen DNA that might be present. Then, the DNA is sequenced and compared with known DNA sequences of bacteria that might be present in the gastrointestinal tract, such as salmonella.

The second less expensive and less work-intensive technique, targeted sequencing, extracts only the DNA in the samples that corresponds with a specific gene sequence. Then the DNA is sequenced and that sequence, which corresponds with only one particular gene, is compared with that same gene sequence in different bacteria found in the gut.

Although Green said there is no “normal” microbiota in the gastrointestinal track of humans on Earth, some general rules guide expectations.

“It’s not a perfect rule, but a healthy human gut microbiota at a high level is dominated by two bacterial phyla – bacteroidetes and firmicutes. Usually the sum of those two phyla represent above 80 percent of the sequences you get back from fecal microbiota,” said Green.

In an unhealthy gastrointestinal tract – when someone has  food poisoning, for example-Green said there is usually a loss of bacterial diversity, leading to a higher level of proteobacteria. Many known human pathogens like salmonella, which can cause illness, are proteobacteria.

Green doesn’t know what they will find when they analyze the samples from the two brothers, but he knows that they will find a change in the bacteria present for someone on a freeze-dried food diet.


Microbiology of the gut affects overall health. Video courtesy of NASA.

“Even if you didn’t go into space and fed yourself dehydrated food, you can expect a dramatic shift in microbial shift,” said Green. “We  definitely will see a change,” but how the change progresses with increasing time in outer space and how quickly the gut return to normal on a normal diet rather is unknown, he said.

Even more interesting than the bacterial change, will be determining the cause of the change.

“The most difficult part [of the study] will be to tease out effects of diet and space flight and which part of space flight is it, living in contained housing, sharing the same space with a limited number of people,” said Green. “Is it circadian disruption?”

Green said a newly published study suggests that when two factors are changed in the human body, the circadian rhythm or sleep pattern and diet, a bacterial change results in the gastrointestinal tract of mice. If they find that the same has happened in Scott’s gut,  this might have interesting implications for soldiers and shift workers who have altered their circadian rhythms and diets.

“One very important aspect that has wide ranging implications on human health is what happens to the microbial community under stress or other conditions like a change in diet. This can change the gut microbial community and the pathogens [present] and can make you more susceptible”to illness, said Green.

Dr. Martha Vitaterna, a neurobiologist at Northwestern University and a researcher for the study, agrees with Green. The study has far-reaching implications outside of longer missions to Mars and space flight, she said.

“The microbiota are very dynamic and respond to environmental, dietary and stress changes that their human ‘hosts’ experience,” said Vitaterna.

“That’s something that will help us here on Earth as well as in future long-duration spaceflight missions,” she said.

Photo at top: Remember trying freeze-dried ice cream? (Ruth Hartnup/flickr)