Nutrition

For long-term stays in an underwater station, a plan for ideal nutrition is required, which takes into account the special circumstances such as increased-pressure environments and reduced sunlight. This section will discuss the specific requirements and the resulting dietary recommendations, which include environmental considerations (avoidance of waste…), safety precautions (avoidance of contamination of the habitat atmosphere…) and alternative sources of supply (own production, finished products…). Some considerations will require a certain design of the corresponding habitat sections.

Image from Wikimedia Commons; Obrer / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Food and Nutrition

Introduction

This section discusses nutritional needs for the crew during underwater missions, as well as design considerations for the food system to ensure nutrition, safety, and acceptability. Food provides both energy and nutrients required for sustaining basic life-support functions and physical work. The different energy requirements during stays in the habitat and during excursions must be taken into account.

Nutrition

Nutrition has been critical in every phase of exploration, from the time when scurvy plagued seafarers to the last century when polar explorers died from malnutrition or, in some cases, nutrient toxicities. The role of nutrition in underwater habitats will be no different.

General Considerations

Nutritional assessments of the Mir and the International Space Station (ISS) crews have documented a range of issues including inadequate caloric intake, weight loss, and decrements in status of individual nutrients (even in cases where intake was adequate).

Nutrient deficiency due to inadequate supply or stability or to increased metabolism and excretion of nutrients can lead to illness and/or performance decrements. Nutritional status has to be adequate before missions to ensure that crews are healthy at the start of the mission.

In the general sense, the primary nutritional requirement is to have a viable and stable food system that the crew is willing and able to consume. The viability of the food system requires not only that food be available for consumption, but that the food has the right nutrient mix to maintain crew health over time. Likewise, a crew’s willingness to consume these nutrients is impacted by the variety and flavor of the food. The risk factors for nutrition in underwater accommodation have a tiered structure, as described following.

1. Inadequate nutritional content available through the food system represents a critical risk. Food may lack adequate nutritional content for several reasons. First, the food available to the crew may be nutritionally deficient when initially provided. Second, the food may lose nutritional value before consumption due to the instability of these nutrients over an extended period of time. Third there is a risk that the habitat environment may impact these foods and nutrients. Radiation (used for food preservation) is known to damage certain vitamins, lipids, and amino acids.

2. Inadequate consumption of food by the crew is also a critical risk. Many crewmembers on long-duration space missions have not consumed adequate amounts of food. On exploration-class missions, food freshness, menu fatigue, stress, and other factors will play a significant role in food consumption, which will in turn impact crew health and performance.

The following factors affect the acceptability of the food and the appetite of the crewmembers:

a. Past experience and personal preference – Generally, a taste for new foods has to be acquired. This is an important consideration with international crews.

b. Variety – Food can lose its acceptance if eaten too frequently. A wide variety of foods is desirable. Food may also be varied by changing the form, texture, and flavor, without affecting nutritional content. The use of colors, shapes, garnishes, and portions in meal presentation, as well as packaging color, utensil shape and size, and visual display of trays may also enhance the eating experience. Long-duration ISS crews have commented that variety is lacking when foods are provided to them in an 8-day cycle. The crew did prefer having foods from the Russian and U.S. menus available at the same time. As of 2007, ISS crews have a 16-day meal cycle, made up of half U.S. and half Russian foods.

c. Availability – Snacks should be available with a minimum of preparation. This is particularly important for high-energy-output tasks such as excursions.

d. Food form – The more normal quality of the food, the more acceptable it will be. This includes the desirability of fresh fruits and vegetables. Precooked frozen food has the highest overall acceptability of the current available methods of preservation.

e. Meal scheduling – Lack of consistent meal periods in the crew schedule can lead to skipped meals and undernourishment.

f. Increased pressure environment – Some habitat crews have reported that changes occur in their taste and odor perception of foods during missions in underwater habitats. There are different possible reasons ,that have to be investigated further.

g. Waste management facilities – Examples from spaceflight missions show that inadequate body waste management facilities have discouraged food consumption in the past

h. Atmospheric contaminants – The buildup of background odors during missions may contribute subliminally to a decrease in appetite and consumption as a result of fatigue or adaptation.

Guidelines for nutrition requirements in spaceflight are documented in “JSC 63555, Nutrition Requirements, Standards, and Operating Bands for Exploration Missions,” JSC NASA Nutritional Biochemistry Group, December 2005, Initial Release (Revision 1) and might be adapted to underwater habitats. They are based on many sources of information that were reviewed at a Nutrition Standards/Operating Bands workshop held March 23–24, 2005, in Houston, Texas. These sources included the set of nutritional requirements defined in 1991 for Space Station Freedom missions, plus the updated set of requirements developed in 1995 (in collaboration with Russian partners) for Mir flights. Workshop participants also evaluated the limited data from short-duration Space Shuttle flights and longer Mir and ISS flights. Data from the ISS included the findings from the Medical Requirement (MR016L, (JSC 28913, 2005)) “Clinical Nutritional Assessment” profile of the first 10 ISS missions, which provided background information about the changes seen in flights of 4 to 6 months (during which time resupply by at least one Progress spacecraft occurred). To establish the nutritional guidelines at the 2005 workshop, the workshop participants in many cases made extrapolations from ground-based space analog studies, and in others had only ground-based nutrition literature for support. The food provided must be of sufficient quality, quantity, and nutrient content to meet the energy demands of various activities while accommodating each crewmember’s individual needs and desires.

Macronutrients

The diet for each crewmember must include macronutrients in the quantities listed in the table below. Macronutrients are nutrients that provide calories for energy: carbohydrates, protein, and fat are essential for crew health.

NutrientsDaily Dietary Intake
Protein0,8 g/kg
Proteinand ≤ 35% of the total daily energy intake
Proteinand 2/3 of the amount in the form of animal
protein and 1/3 in the form of vegetable protein
Carbohydrate50–55% of the total daily energy intake
Fat25–35% of the total daily energy intake
Ω-6 Fatty acids14 g
Ω-3 Fatty acids1.1–1.6 g
Saturated Fat< 7% of total calories
Trans fatty acids< 1% of total calories
Cholesterol< 300 mg/day
Fiber10–14 grams/4187 kJ

Micronutrients

Although macronutrients are very important, they are not the only things we need for survival. Our bodies also need water (see corresponding section Water) and micronutrients. Micronutrients are nutrients that our bodies need in smaller amounts, and include vitamins and minerals. (a detailed list of micronutrients and their recommended quanitities is available in HIDH, NASA/SP-2010-3407, chapter 7.2.2.4.)

The ISS food system includes vitamin D tablets, since vitamin D deficiency is a common issue for astronauts. Any other vitamins provided are per the agreement between the individual astronaut and his or her flight surgeon.

The storage temperature of foods has a direct impact upon the shelf life of the foods, including the quality of nutrients available when the food is consumed. For example, foods will maintain the best quality for the longest times when frozen (0°F). At temperatures above freezing, spoilage and degradation increases appreciably.

Food for the Space Shuttle and the ISS is packaged in a vacuum environment, since the elimination of oxygen in the package is essential to minimize the rate of rancidity. Atmospheres with abnormally high concentrations of oxygen may result in increased rates of rancidity and nutrient depletion for certain shelf-stable foods.

Food System

This section discusses the food system, including types of food and packaging, storage, preparation, and cleanup.

Galley Area

The galley area, as well as the accommodation of the food preparation equipment, must be designed and sized to allow all crewmembers to eat meals at the same time. On ISS, and when possible on the Space Shuttle, crews have preferred to eat meals together to promote unity. Sometimes, such as during crew handovers, the number of crewmembers to be accommodated will be larger than usual.

Location

The galley should be located in an area that is conducive to conversation and relaxation, and not in an area with high traffic flow. The ISS Service Module galley area has been described as noisy because of work, exercise, and fans. Proper lighting conditions must be provided, to ensure that food can be properly seen and spills can be quickly identified. Location in relation to waste and hygiene areas is also important to consider. ISS crews have noted that co-locating dining areas with waste and hygiene areas is not optimal for sanitation or psychological purposes. Apollo crew members have also indicated that the galley was too close to the waste management system, and odors from that area resulted in a loss of appetite. The galley must be isolated from waste and hygiene areas to prevent contamination of food by  microorganisms in those areas in addition to preventing odors from permeating the eating area.

Contamination

Location of the food system and food storage should ensure there is no contamination from waste and hygiene areas. Microbiological contamination of food can negatively impact crew health. This can be avoided with the proper processing of food, as well as the design of the food system and habitat. The ability to clean and disinfect the habitat will also help to minimize microbial contamination of the food system. Any chemicals on board must be stored to avoid the contamination of any food in storage or during eating.  Contamination of the food system by physical debris can jeopardize the safety and health of the crew.

Food Preparation, Consumption, and Cleanup

Heating and Cooling

The ability to heat foods and drinks should be provided. When provided, food and drink must be heated to between 68°C (155°F) and 79°C (175°F). Heating food and liquid enhances the palatability of some items, which is important for behavioural health as well as ensuring that crewmembers eat the food provided. Based on input from Apollo astronauts and NASA’s current crewmembers, it is essential to have hot water for beverages and to hydrate appropriate foods with hot water. Not only does the crew want their hot coffee (one of the most requested items) but if the food is not palatable, they will not eat the food. Furthermore, if they don’t eat the food, they will not get enough calories and will not have adequate energy to do their tasks (and think clearly).

The ability to cool some foods and liquids to around 4°C (39°F) should be provided. Cooling enhances the palatability of some food and drink items, which is important for crew dietary and behavioural health. Also, consideration should be given to providing the ability to refrigerate food packages that have been opened but the food not completely consumed, for consumption at a later time.

While heating food and liquid may require power from the habitat, there may be ways to use the heat from several sources in the habitat for the galley, instead of radiating it into the sea. Cooling, on the other hand, may require more energy.

Preparation Time

Food systems should be designed to minimize food preparation time, to allow all crewmembers to eat together in a 1-hour mealtime. One way to make efficient use of crew time is to minimize food preparation time. Typically, mealtimes have been scheduled for 1 hour, and include not only eating but unstowing of food items, food preparation, cleaning, and stowage of trash and meal-related items. Food preparation time may depend on the size of a food warmer and its ability to heat quickly, as well as food packaging design and other variables. It should also be taken into account that some food preparation techniques such as boiling and baking have different parameters in high-pressure environments.

Cleanup

Because food substances left on cleaning materials and in packaging will spoil, food system wet waste materials must be properly disposed of and contained to limit microbial contamination. Waste generated from the food system will include both wet and dry materials. Dry materials may include items such as packaging of dry foods, while wet materials may include leftover food, cleaning materials, and wet food packaging materials.

Food Types and Packaging

To maintain food quality throughout a mission, the type of food and packaging should be carefully considered. However, the relatively quick access to the coast does not meet the requirements for long shelf life of food as in space flight programs. On the other hand, the further the habitat is located in the open sea, the more the recommendations stated in HIDH, NASA/SP-2010-3407, chapter 7.2.3.3 should be applied. A certain stock of food for the case, that delivery from land is halted due to bad weather conditions, should also be considered.

Beverages

As drinks for an underwater habitat, most freely available products can be considered. Further investigation is required to evaluate the effects of increased pressure on carbonated beverages, and these beverages on human physiology.

Food Preparation and Processing

The preparation equipment for the galley will likely be commercially available gourmet kitchen appliances that will need to be modified for underwater habitats. Some packaged food would likely be required.

Food preparation or processing in a habitat will depend on these factors:

  • mass and volume of the preparation and processing equipment
  • required resources such as power, crew time, and water
  • types of foods able to be processed
  • safety concerns to ensure crew health
  • desired shelf life
  • effects of increased pressure

Supplementary Products

A complete or partial supplement could be a food replacement like Mana. MANA is a balanced food providing “all nutrients the human body needs”. It comes in the form of drink or powder being produced in Prague. Learn more on their webpage.

To be added:

The possibility to produce own food, see webpage of InFarm as reference


Note: This article contains adaptations from the Human Integration Handbook (HIDH), NASA/SP-2010-3407

Please also take into account: Nutritional considerations during prolonged exposure to a confined, hyperbaric, hyperoxic environment: recommendations for saturation divers, S. K. Deb, P. A. Swinton and E. Dolan

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