The explanation that I find most likely is a reduction in water intake. Weight loss can indicate a reduction in fat mass or lean mass, but it can also indicate a reduction in water mass, or dehydration. The food in the experimental condition was purposely designed to provide sufficient calories while being lower in mass and volume than everyday food. One of the best ways to create energy-dense food is to reduce water content . Consequently, the food in the experimental condition had lower water content than the food in the control condition. It is therefore likely that participants consumed less water from food during the experimental condition, and that they did not sufficiently make up for this difference by drinking more fluids. This hypothesis is supported by the results of the post hoc analyses, described below. In the post hoc analyses, it was found that participants in the experimental condition reported consuming 2,800.82 total grams of food + fluid each day, whereas participants in the control condition reported consuming 3,180.42 total grams of food + fluid each day. Therefore, participants in the experimental condition reported consuming an average of 379.6 grams less over the course of a day, even though they did not consume fewer macro-nutrients .
Aside from macro-nutrients,container vertical farming the weight of food usually results from a substantial amount of water and a small amount of fiber and alcohol, along with a relatively small amount of ash . Consequently, it appears likely that participants in the experimental condition consumed less water. This would not be surprising, given that the experimental food was designed to be energy dense. In support of this theory, participants in the experimental condition lost an average of 2.157 pounds, or 1.25% of their body weight, which can easily occur from dehydration. Some researchers have defined mild dehydration as a 1-2% decrease in body weight, moderate dehydration as a 2-5% decrease in body weight, and severe dehydration as a 5% or greater decrease in body weight . It is possible that during the experimental condition, participants consumed less water from food and fluids, resulting in mild dehydration that contributed a 1.25% decrease in body weight. For comparison, when participants were in the control condition they lost 0.04% of their body weight. If participants were, indeed, mildly dehydrated during the experimental condition, is this a cause for concern? During the experimental condition, participants consumed approximately 2,410.82 grams from non-energy-yielding sources . Even if the ash and fiber comprised 15% of this mass, participants would have consumed over 2,000 grams of water – the minimum intake required by NASA, based on participants’ average caloric intake in this study .
Additionally, decrements in cognitive or physical performance usually do not occur until individuals have lost 2% or more of their body weight . Indeed, during the experimental condition, participants showed no significant changes in psychological or physical outcomes other than decreased weight. These factors would indicate that any mild dehydration experienced by participants is little cause for concern. However, although NASA’s ISS requirements stipulate astronauts should receive at least 2 liters of water a day, the Institute of Medicine recommends more than that . Furthermore, numerous factors make it impossible to determine whether sufficient water was consumed in the experimental condition: participants’ fluid reports were questionable, participants were allowed to consume caffeine, and participants did not record their exercise. Nevertheless, at present, the data do not indicate participants were worrisomely dehydrated while eating the experimental diet. In future studies of commercial space food, incorporating measures that can differentiate between fat mass and lean mass and measures that can assess changes in dehydration would help to determine the cause of weight loss.NASA’s ISS requirement is that astronauts be provided with 12-15% of their calories from protein, 30-35% of their calories from fat, and 50-55% of their calories from carbohydrates . The Institute of Medicine sets forth adequate macro-nutrient proportions of 10-35% of calories from protein, 25-35% of calories from fat, and 45-65% of calories from carbohydrate. During the experimental condition, participants met both NASA and the Institute of Medicine’s recommended macro-nutrient proportions.
During the control condition, participants exceeded NASA’s protein and fat requirements, and failed to meet the lower limit of NASA’s carbohydrate requirement. During the control condition, participants also consumed fat in excess of the Institute of Medicine’s recommendations. In summary, during the experimental condition, participants consumed macro-nutrients in the recommended proportions, whereas during the control condition they did not.Participants expressed a desire for more animal protein, indicating that satisfaction with the diet may increase if more animal protein were added. Increasing the amount of animal protein in the diet could also assist with assembling a low fiber diet, which I aimed to achieve but which was difficult to attain, as many “healthy” prepackaged foods are high in fiber. Increasing the amount of protein in the experimental diet would not necessarily be unhealthy, as 14.5% of calories in the diet came from protein, and the Institute of Medicine’s upper limit for protein is 35% . However, NASA has an upper limit of 15% because a high protein diet, especially one from animal sources, could lead to hypercalcemia and increased risk of developing renal stones . Renal stones are especially a concern for astronauts as physiological changes during spaceflight may already lead to increased risk of renal stone formation . Consequently, there is rationale for keeping protein intake relatively low. As discussed in Table 1, given that many of the foods in the experimental diet contained a mix of animal and vegetable proteins, and that I did not have access to a calorimeter, it was not possible for me to calculate the experimental diet’s percentage of protein from animal vs. vegetable sources. However, based on a visual analysis of the types of food in the experimental diet, it is possible that diet did not meet NASA’s recommendation to have 2/3 of protein come from animal sources . It therefore seems advisable to at least shift away from plant-based protein bars and toward more substantial animal sources, such as peppered beef jerky. Various brands and varieties should be investigated to identify a meat source that is tender, salty, spicy, and substantial enough to provide a “meal-like” sensation,hydroponic vertical garden without exceeding the sodium limit and without having small pieces that could flake off and float away in a microgravity environment.NASA only includes items that score, on average, 6.0 or higher on the 9-point Hedonic Scale. In this study, participants rated 50% of the experimental diet items as 6.0 or higher. Because these items were so well liked, I recommend keeping these items in the diet. See all green-colored items in Table 10 for a list of these foods. Nearly one-third of the items in the experimental diet were rated between 5.0 and 5.9. These foods were rated below NASA’s acceptable score of 6.0 and their elimination should therefore be considered. However, it’s not clear that participants’ ratings in this study were equivalent to NASA’s food ratings because in this study, participants ate and rated the food in a naturalistic setting, rather than in a laboratory. Research has shown that the environment can greatly impact food ratings; individuals rate food differently depending upon whether they are in a laboratory, a restaurant, or a cafeteria . In this study, participants may have eaten in the cafeteria with colleagues, alone at their desk, or at home.
Sometimes, when they ate, they saw just their own food, and atother times they saw a plethora of freshly prepared food that their colleagues were eating, yet which they could not eat. Consequently, it is not clear how the multiple environments in this study should be categorized and how participants’ ratings would have been different, had they been doing a taste test in a laboratory. Furthermore, some items that received a mean rating between 5.0 and 5.9 were controversial, meaning that some participants loved them and some hated them. Consequently, when designing future versions of the experimental diet, I recommend that these 5.0- to 5.9- scored items be put back into the pool of options for consideration. Instead of eliminating all these items, perhaps reducing their frequency would be wiser. For instance, all three noodle/potato entrées received mean ratings between 5.0 and 5.9. Yet one participant specifically requested more of these items, indicating a strong preference for them. Keeping just one noodle entrée in the menu may be a better choice than eliminating them completely. However, eliminating all 10 items that were rated lower than 5.0 is advised. Because participants were provided with over 3,000 calories a day, these 10 items could be completely removed from the diet while still providing over 2,400 calories per day – well over the 1,810.71 calories that participants, on average, consumed each day of the experimental condition. Removing these 10 items from the diet would still provide crew with 38 different food items for their 4-day trip and would, if the ratings for the remaining food items did not change, raise the mean food rating of the diet to 6.18 on the Hedonic Scale. All experimental food had to be eaten at room temperature. Room temperature food is less odiferous than heated food, and I had therefore anticipated the smell of food would not be a strong factor in food choice. Consequently, participants were not asked to rate the smell of foods. However, the strong odor of certain foods became apparent to me while evaluating leftovers. This experience highlighted a major difference between the study environment and the Crew Transportation Vehicle: in the study, the open-air setting likely muted the smell of foods, whereas in the enclosed Crew Transportation Vehicle, the smell of foods would be easily noticeable. This is a concern because smells could exacerbate the symptoms of space motion sickness, which is commonly experienced by astronauts during early flight. Former astronauts have recalled that, “Even if the sick people wisely stuck to broth and crackers, odors from the meals being enjoyed by those fortunate enough to feel better could be overwhelming. Some commanders made the law of ‘no stinky food on day 1 or 2.’ That precluded such odiferous items as tuna, salmon, or beef with barbeque sauce” . It would therefore be wise to remove strongly odiferous foods from the diet. The odor of foods could be evaluated in the same way that materials used in spaceflight are evaluated, by having panelists rate the smell from 0 = “undetectable” to 4 = “revolting” . Foods that are rated 2.5 or higher could be eliminated from the diet . Another factor that became quickly apparent was the large variation in participants’ food preferences. Some participants craved the noodle entrées whereas others said the noodles were inedible. Food choice is impacted by not only the qualities of the food itself, but also demographic , sociocultural, and economic variables . When NASA initially designed the Space Shuttle menu, a standard menu was developed for all missions . After four missions, the menu was changed to be crew-selected, so that crew could provide input but all crew members were ultimately provided with the same food. However, crew members expressed a desire for even more personalized menus, and consequently starting with the seventh Space Shuttle mission , individualized menus were provided for each crew member. Crew members were allowed to select the food they wanted from a menu of over 350 food items. Crew members’ choices were then analyzed by a dietitian, who would recommend substitutions to obtain a balanced diet. Based on the large variation in food preferences observed in this study, it seems the individualized menu would be better for achieving high food satisfaction than the standard menu. However, most commercial aerospace companies hope to fly not just eight astronauts a year, but hundreds. Personalizing the diet for each astronaut could become onerous. Instead, I recommend letting crew members pick the food they want from a collection of 100+ food items. Each crew member could be provided with a container and be allowed to select whatever food they wanted as long as it fit in that container and met certain mass restrictions.