Yet during these early flights, astronauts were losing weight . Caloric provisions were increased to 2,750 calories a day during Project Gemini , but still, astronauts were losing weight . It wasn’t until Project Apollo and Skylab that it was realized the assumption astronauts required fewer calories was wrong. Human total energy expenditure while in microgravity was actually similar to that while on Earth , and astronauts therefore needed as many calories in outer space as they did on ground: approximately 3,000 calories a day for an active male . However, a diet of 3,000 calories can come from many sources. What food sources should be included in an astronaut’s diet? This was a major point of investigation on Skylab. During Skylab flights, NASA conducted the most extensive studies of nutrient metabolism in outer space to date . Astronauts recorded all the food they ate, collected biological samples, and underwent numerous nutritional experiments. For three weeks before and after Skylab flights, astronauts also ate the same food that they would have eaten during flight, so that researchers could investigate how spaceflight – rather than the space food – altered metabolism . Data from these and other studies showed astronauts experienced various physiological changes that slightly altered their needs for a few micro-nutrients . Yet for the most part, astronauts’ nutrient needs remained the same, and they needed just as many calories in space as they did on ground. Astronauts therefore required essentially typical diets . NASA’s current nutrient requirements are shown in Table 1. However, even when astronauts were provided with sufficient nutrients, they often did not consume sufficient amounts. Historically, astronauts have consumed far fewer calories than were provided to them . It was only during the Skylab missions that astronauts consumed their recommended caloric intake, and this was likely because Skylab had many things that missions before and since have not had: a dining room table, a refrigerator, a freezer that contained ice cream and steak,vertical gardening in greenhouse and extensive studies that required astronauts eat certain foods .Astronauts’ food intake since Skylab has failed to meet NASA’s requirements, despite NASA providing sufficient food on Space Shuttle flights and on stays at the International Space Station .

On the Space Shuttle, astronauts ate about 1995 calories a day . Currently, ISS astronauts self-report eating about 80% of their recommended caloric intake . NASA can encourage astronauts to eat more food, but ISS astronauts live hundreds of miles away from NASA’s headquarters, and consequently astronauts can eat what they please. The amount that astronauts eat is often less than what NASA would prefer. There are likely many reasons for this under eating, but one historical factor has been low food satisfaction. Food satisfaction is multifaceted, but three aspects of food satisfaction that became apparent to NASA early on, and which will therefore be used as operational definitions of food satisfaction in this study, were acceptability, familiarity, and variety . Acceptability refers to the extent to which a food is hedonically pleasing. In other words, how much does one “like” the food? Highly acceptable foods are highly palatable and lead to increased food intake , whereas foods that have low acceptability lead to decreased food intake . NASA evaluates the acceptability of food items prior to flight via on-ground taste tests, during which time future astronauts taste food items and rate them on the 9-point Hedonic Scale . The Hedonic Scale asks participants to rate a food item from “dislike extremely” to “like extremely.” Items rated as a 6.0 or higher are deemed “acceptable” by NASA and can be considered for use in flight . Familiarity refers to the extent to which a food item looks, feels, tastes, and otherwise resembles food one has eaten on a regular basis . For example, steak with a side of vegetables is familiar, whereas a tube of pureed beef and vegetables is not. Sugar cookies are familiar, whereas sugar cookies compressed into cubes and coated with gelatin to prevent crumbling are not . Both “Pureed Beef and Vegetables” and “Sugar Cookie Cubes” are former space foods. Although these foods may have started with familiar ingredients, the final form of the food had unfamiliar textures and “mouth feels” and consequently these foods had low familiarity. Astronauts prefer to eat foods that are familiar and tend to eat less of foods that are unfamiliar . Variety refers to the extent to which there is variation in a diet. A diet with insufficient variety is monotonous, and a diet that is monotonous leads, in time, to decreased acceptability and decreased food intake. Researchers have found through laboratory studies that eating the same food for five days in a row decreases acceptance ratings and intake of that food . People prefer variety in their diet and eat more food when presented with various food options .

When NASA was first producing food for Projects Mercury and Gemini, the importance of variety and familiarity were not yet fully known. However, it was obvious to NASA that the food must be nutritious and acceptable. NASA therefore made sure to provide nutrition-filled foods that were rated acceptably in on-ground taste tests. Nevertheless, in an effort to reduce the weight, volume, and messiness of the food, NASA food scientists put the foods into pureed and cubed form, and consequently the familiarity and variety of the foods was decreased. As a result, astronauts did not consume sufficient calories during flight . To alleviate the problem of under eating, NASA overhauled the food system during the Apollo program and started to provide astronauts with fewer tubed and cubed foods and more dehydrated, irradiated, and thermostabilizd foods . These treatments prolonged food shelf life while also providing more acceptability, variety, and familiarity in the diet. Some of these foods could even be eaten with a spoon, much like how food is eaten on ground . NASA has continued to strive for increases in the acceptability, variety, and familiarity of space food, and as a result, astronauts’ satisfaction with space food has increased. However, food intake remains below goal and there continues to be room for improvement. For instance, astronauts are separated from their families by hundreds of miles, living in a confined, isolated environment with colleagues for months on end – and they don’t always get along. As evidence, ISS astronauts kept journals as part of a study that ran from 2003 until 2016, and these journals reveal crew members can, at times, be inconsiderate and bothersome, and occasionally even argumentative. As one astronaut wrote, “I was really livid after Z snapped at me quite viciously about something that wasn’t my fault. I let Z have it, like I can’t remember ever before in a professional relationship, and stormed off” . Another stressor is that astronauts are provided with strict schedules by Mission Control, leading to numerous daily hassles such as not having enough time to get everything done. As one astronaut wrote in a journal, “Today was a hard day. Small things are getting to me. I am tired. I think that the ground is scheduling less time for tasks than before. So, there is very little, if any fat left in the schedule for me to use to catch up on little things during the day” . Difficulties with sleep, personal hygiene, and expectations from both oneself and others are also stressors. These stressors can impair morale and psychological health . However, morale and psychological health can be improved with satisfying food, as has been shown in on-ground and in-flight studies . On-ground, in laboratory studies, researchers have found that eating a well-liked food improves mood,greenhouse vertical farming whereas eating less-liked food does not . In space, astronauts on both Skylab and the ISS have reported the importance of food in improving mood, decreasing stress, and promoting feelings of social connection.

For instance, the Skylab 2 crew recounted fond memories of smothering ice cream with strawberry sauce and eating together as they watched Earth out the window . ISS astronauts’ journals also reveal the importance of food in improving mood and stress: “Almost supper time! It’s amazing how meals become the high points of the day sometimes” , “The good news is that we have good food on board now. It makes such a huge difference in mental attitude” . Astronauts’ journals also show how food can impact social connectedness: “We had a great dinner last night. Even X took a break from packing to enjoy the company and camaraderie. It was a testament to the unique bonds we all have from sharing the experience” , “We ate together and talked and laughed. It was a good day for our crew” .Satisfying food can clearly benefit psychological health. Yet disappointment with the acceptability, variety, and familiarity of food can also lead to psychological problems, as shown in other ISS astronaut journal entries: “The food is getting somewhat old to us . . . it is starting to all look and taste the same” , “Last week was difficult and long. Probably seemed like it, because of the food situation” , “Food is still our biggest concern. We are out of side dishes, such as potatoes and vegetables” . As these entries show, dissatisfaction with food can lead directly to psychological difficulties, such as frustration and stress. Yet dissatisfaction with food can also lead to psychological problems through the mechanism of under eating. People eat less of food that is not sufficiently satisfying , and if food intake is inadequate for an extended period of time, it can lead to severe psychological consequences. In Ancel Keys’ Minnesota Starvation Experiment , where 36 men ate approximately 1,560 calories for six months, participants experienced numerous psychological problems, including moodiness, depression, irritability, social withdrawal, and preoccupation with food . Restricting caloric intake has also been shown to increase salivary cortisol, a biological indicator of stress . Even having to monitor one’s diet can lead to increased perceived stress , and food monitoring is something that astronauts routinely engage in when they audit their food stocks, when they ration their food supplies, and when they complete their weekly Food Frequency Questionnaire . Psychological harm resulting from un-satisfying food or insufficient food intake is particularly worrisome when it comes to spaceflight because emotional stability, social skills , and ability to work under extreme stress are important human factors in the success of space missions . NASA carefully selects astronauts to have these and other personality traits that will enable them to excel in the isolating, confined, and hazardous conditions of outer space . Yet no matter how carefully selected, astronauts do experience psychological problems. During flight, astronauts can experience irritability, anxiety, loneliness, superiority complexes, low morale, and difficulties concentrating , which can impair astronauts’ ability to carry out missions. For instance, during the Skylab 4 and Apollo 13 flights, irritability and interpersonal conflict among crew members and between crew and ground controllers became so intense that the crew took time off of work to resolve difficulties . Given that astronauts can experience psychological problems during flight, and given the research showing that insufficient food intake and unsatisfying food can contribute to psychological problems, whereas satisfying food can contribute to psychological health, the importance of providing astronauts with a satisfying diet is clear. However, aiming to provide foods that benefit psychological health and actually doing so are two very different things. NASA has long aimed to use food as a mood booster through providing food that looks and tastes “home cooked” . Yet as mentioned earlier, the food fell short in many ways. Consequently, when designing new space food diets, it is important to assess the food’s actual impact on psychological health. Given that emotional stability, teamwork, and ability to work under extreme stress are among the most important factors in the success of space missions , it is especially important to assess the impact of new space food diets on mood, social connection, and perceived stress.Dissatisfaction with food can lead to decreased food intake , and inadequate food intake can result in numerous harms to physical health. Three harms that are particularly concerning when it comes to astronauts are weight loss, sleep difficulties, and poor self-reported health. Weight loss in astronauts is both common and dangerous.