When humans lose weight, either in outer space or on Earth, this weight is in the form of both lean body mass and fat mass . In non-astronaut populations, the goal of weight loss is usually to lose more fat mass than lean body mass. Indeed, when healthy, ambulatory humans lose weight on Earth, most of this weight is in the form of fat mass, with a lesser percentage of the lost weight coming from lean body mass . However, when humans are not ambulatory, as is the case with astronauts during transport, a larger percentage of the lost weight can come from lean body mass. In one crossover study – a type of study in which the same participants are exposed to all conditions – Biolo and colleagues tested the consequences of a weight-loss diet versus a weight-maintenance diet during either ambulatory or non-ambulatory conditions. When participants were on the weight-loss diet and ambulatory, most of their weight loss was in the form of lost fat mass rather than lean body mass . However, when participants were on the weight-loss diet and bed rest, their weight loss was in the form of similar amounts of lost fat mass and lean body mass . In other words, weight loss coupled with inactivity leads to greater loss of lean body mass. The loss of lean body mass is already a phenomenon that occurs in human and nonhuman animals living in micro-gravity . Therefore, weight loss could exacerbate this loss of lean body mass in astronauts, which could lead to the loss of muscle volume and the loss of bone mineral content . These outcomes could lead to increased risk for soft tissue injury , bone fracture, and decreased stamina , which could increase astronauts’ risk of being injured during extravehicular activities and of having difficulty readjusting to gravity on Earth or other planets. In summary,vertical agriculture when astronauts are in a micro-gravity environment, and especially when they are physically inactive, such as they will be in the Crew Transportation Vehicle, weight loss could result in the loss of lean body mass.
Consequently, assessing the impact of space food on weight loss will be important. Sleep difficulties are also common in astronauts. Astronauts sleep significantly less during ISS missions, as compared to after, and 75% of ISS crew members report using medications to promote sleep . The most frequently used sleep medication during spaceflight is zolpidem , a medication with side effects that can include difficulty with balance, unusual dreams, headache, gastrointestinal problems, and feeling “drugged” . Despite the common use of this and other sleep-promoting medications among astronauts, and despite a NASA mandate that astronauts have 8.5 hours for sleep per night, ISS astronauts average only 6.09 hours of sleep a night . Sleeping 6 to 6.9 hours a night was shown in one epidemiological study of over 175,000 people to significantly increase the risk for work-related injury . Sleep deprivation has also been linked to psychological impairments such as negatively biased mood, difficulty using one’s emotions to make decisions, impaired frustration tolerance, and reduced attention, vigilance, and memory . Even when alertness is restored with stimulants such as caffeine, many of these impairments remain . Astronauts have access to coffee, caffeine pills, and stimulant pills, such as modafinil . Yet their journals still report numerous instances of sleep deprivation leading to impaired functioning, such as “I fell asleep while typing” and “The fatigue was evident when a couple of minor mistakes were made today on some payload activities . . . it is an obvious indicator of fatigue” . Astronauts’ sleep deprivation could pose a serious threat to both themselves and to the success of space missions . Factors that can exacerbate sleep difficulties should therefore be avoided . Food is one such factor that could exacerbate sleep difficulties. In a nationally representative study of 5,587 U.S. adults, eating a reduced-variety diet, consuming less salt, and consuming a low number of calories was associated with self-reports of sleeping less than five hours a night, as compared to self-reports of sleeping 7 to 8 hours a night . The researchers also found significant associations between sleep duration and the intake of numerous nutrients, including intake of carbohydrates, proteins, vitamins, and minerals . In summary, aspects of food intake have been associated with impaired sleep, and because astronauts already have sleep difficulties, it is important to evaluate how new space food diets impact sleep.
Unlike sleep difficulties and weight loss, poor self-reported health is not often emphasized by NASA as a potential health risk. However, asking participants to rate their own health as excellent, very good, good, fair, or poor is well recognized in health fields as a robust, reliable, and valid way to assess overall health status . Self-reported health, also called self-rated health or perceived health, predicts functional ability and mortality . Self-reported health predicts mortality even after controlling for numerous potential confounds such as age, sex, income, education, and health practices . Asking participants to rate their own health is a robust predictor of health outcomes, even when the wording of the question varies . Self-reported health is usually used as an indicator of health over long time periods, but researchers have found that participants’ ratings can also change over relatively short periods of time, indicating that self-reported health could be used as a marker of short-term changes in health. For instance, when 9,235 participants in the 2005-2008 National Health and Nutrition Examination Survey were surveyed at two time points one month apart, nearly 40% of participants changed their response to the question, “In general, would you say your health is excellent, very good, good, fair, or poor?” . Additionally, when a variant of the self-reported health question, “Overall, how satisfied were you with your health today?” was used in a 56-day survey study, researchers found significant day-to-day, within person variability . Greater day-to-day health satisfaction was also associated with fewer health events . Consequently, although self reported health is traditionally used as an indicator of health over long time periods, it can likely also be used to assess variation in self-reported health over days or weeks. Self-reported health could therefore be used to assess how new space food diets impact health over time.To ensure participants were representative of future commercial astronauts, all participants had to express an interest in traveling to outer space. Participants also had to be willing and able to eat breakfast, lunch, and dinner at work Monday through Thursday for two weeks. Additionally, participants had to be willing and able to eat only the food provided during the experimental condition and to eat from a restricted number of food venues at the workplace during the control condition. These eligibility requirements were anticipated to increase study adherence. Participants also had to report no endocrine or metabolic disorder, as eating the processed, ready-to-eat food could have exacerbated these disorders. Finally, participants had to report no current dieting and no history of an eating disorder, as these factors could have adversely impacted participants’ eating or rating of the foods. UCLA Institutional Review Board approval was obtained prior to conducting study procedures.
A parallel crossover design was used over the course of two weeks. The parallel crossover design was selected because this type of design achieves greater statistical power and precision with fewer participants, as compared to a parallel design , and recruiting participants from the pool of commercial aerospace employees was anticipated to be difficult. For the parallel crossover design to be most effective, a “washout” period between conditions is required . Therefore, this study involved food manipulation Monday through Thursday with a three-day “washout” period Friday through Sunday. During this washout period, participants ate as normal without recording their food intake. During week 1, half the participants were randomly assigned to the experimental condition, while the other half were in the control condition. During week 2, this arrangement flipped,vertical farming aeroponics with the participants who were previously in the experimental condition switching to the control condition, and vice versa. Both the experimental and control conditions lasted 4 days in Week 1 and 4 days in Week 2 . All participants completed the study during the same two-week period. The procedure is shown in Table 3. Each week of the study required approximately 107 minutes of the participant’s time. Participants also completed a brief qualitative assessment at the very end of the study, which took approximately 10 minutes. This brought a participant’s total time commitment to 224 minutes, or approximately 3.75 hours, for the entire study.Regardless of the condition to which they were assigned, participants met me in a workplace conference room between 8:00am and 10:00am on Monday morning. At that time, they received their condition instructions , along with a bullet-point list of foods they could and could not week eat that week. All participants were reminded they would be weighed right then and on Friday morning, before eating. They were also reminded they would receive an email with a link to an online survey at 5:00pm on Monday, Tuesday, Wednesday, and Thursday of both weeks. Finally, all participants were told they would receive text message reminders to complete the survey at 6:00pm and 7:00pm each night, and they were expected to complete the survey before 8:00pm. Participants were asked to complete the survey on a computer, rather than on a smartphone, so that all questions would display in correct formatting. The time frame of 5:00 to 8:00pm was chosen for the evening survey because participants often remained at work until 7:00pm or later, and I expected participants would be more likely to complete the survey if they completed it before leaving work. However, data were not discarded for being submitted after 8:00pm.When participants met me on Monday morning, they received their tote of experimental condition food. The tote included four gallon-sized plastic bags, with each bag containing one day’s worth of food. The bags were labeled Day 1, Day 2, Day 3, and Day 4. Each gallon-sized bag contained four smaller plastic bags in which the food was actually stored. These bags were labeled Breakfast, Lunch, Dinner, and Snack. Participants were also provided with a binder that showed the breakfast, lunch, dinner, and snack options that were provided for each day. Participants were informed that the meal categories were recommendations only and that they could eat anything from the tote at any time. Because the food was designed to be lightweight and portable, participants were able to carry the tote with them everywhere they went. All totes contained the same exact food . This food was designed to provide sufficient calories for all participants. All totes also included eight empty two-gallon-sized plastic zip bags for storing leftover food. When participants met me on Monday morning, they received vouchers for four days of meals at work, the control condition instructions , and four Food Rating Logs . The control condition instructions outlined that, for the next four days, they would be allowed to eat from the workplace food outlets that served restaurant-style, pre-determined portions . This provided participants with approximately 12 meal options at any time of the day. Participants were not allowed to eat from the cafeteria-style line at work, nor were they allowed to eat from the graband-go venue, with the exception of the yogurt, milk, and cereal that was served at that venue. Participants were also not allowed to eat from the frozen yogurt stand or from the specialty coffee stand. Restricting participants from these foods had the benefit of allowing me to more accurately estimate their nutritional intake and to provide the experience of seeing food yet being unable to eat it. This experience, of seeing food and being unable to eat it, will not occur in outer space. Therefore, providing this experience in both the experimental and control conditions provided feelings of deprivation in both conditions, thereby effectively eliminating this deprivation from being a cause of different responses to the two conditions. Prior to starting the study, participants completed a Work-Specific Food Survey . This measure was used to screen participants and to provide descriptive information on the sample. This measure was not used as a moderator in any analyses. On Friday, participants also completed the Ten-Item Personality Inventory . This measure was also used to provide descriptive information on the sample and was not used as a moderator in any analyses.