By Ray R. Collins

 

Note: references may not work until I finish linking my personal site with ISECCo's web site.

 

The Mars Base Zero diet is primarily limited by calories.  Both from the point of producing enough for supporting a person, and from the point of having them in a form concentrated enough so the consumer doesn't have to eat too much food in one day.  For example to obtain 3,000 k-calories from potatoes you would have to eat more than 6 pounds every day!  This is more than most people can comfortably consume in a day.

 

To begin with, let us look at what we have available for planting.  The gross size of the greenhouse is 24 ft by 36 ft, or 864 square feet.  From this we need to subtract the chicken cage/compost heap (the chicken cage is located over the compost), an area of 16 square feet.  Our primary walkway is 8 inches wide and 24 feet long, for a total of 16 square feet.  (We also have side walkways, but we have pots on them, so they are included in the available growing area.)  To get to the primary walkway we need some steps, probably 10.  If each step is 2/3 of a square foot, this is 6 square feet.  The area with the planting trays has a (limited) number of aisles down it; an E/W aisle, and a N/S aisle.  The E/W is 18 inches wide and 12 feet long, and the N/S is 18 inches wide and 20 feet long.  In addition there is another aisle in front of the grow bench that is 18 inches wide and 8 feet long.  These aisles total 60 square feet.  So we are left with a total of 766 square feet of growing area (864-16-16-6-60).

 

To develop the diet we approached determined that a minimum of half the needed 3,100 k-calories (RDA for a person of my size) would be from potatoes.  Our productivity is estimated at 0.75 pounds/sq ft/75 days, or 0.01 pound/sq/day.  Since we will need 1550 k-calories, we will need 1550/495 k-cal (per pound of potato) = 3.1 pounds per day of potatoes.  This value is put into the nutritional calculator.  To produce 3.1 pounds per day of potatoes we will need 310 square feet planted in potatoes.  We are thus left with 456 square feet of growing area.

 

We know that we will be producing an egg a day.  So we can add this to the nutritional calculator.  The chicken cage has already been subtracted from the growing area.

 

We will be producing about 100 grams a day of strawberries, so this too is added to the nutritional calculator.  The majority of the strawberries are in hanging baskets, so they take up little space.  But we will need a small amount of space, so subtract 15 square feet for the strawberries, leaving 441 square feet of growing area.

 

At this point we should pause and examine what nutrients we are missing.  Although we only have 53% of our k-calories, we have met 100% of our amino acid needs (due in large part to the egg), though only about 60% of our bulk protein requirements.  The most critical thing we are missing is vitamin A, for we have only achieved 6% of the RDA.

 

Carrots are an excellent source of vitamin A, so we shall plan for a carrot a day.  To provide a continuous supply of carrots at a carrot a day we will need to plant about 7 square feet, leaving 434 square feet of growing area.  The next lowest dietary item is calcium.  Doing a search on calcium (limited to what we can produce in our ecosystem) we discover that spinach, soybeans, turnip greens and white beans are all good sources.  Spinach is the highest, so we want to eat a cup of spinach a day.  Though we lack specific growth data on spinach we estimate that 12 square feet will be needed, leaving us with 422.

 

We still have only achieved 35% of the calcium we need, but selenium is now the lowest at only 20% of RDA.  Whole wheat is an excellent source of selenium (and good for adding calories to the diet), so we shall add in a cup of whole wheat flour.  To make a cup of flour we will need about 2/3 cup of wheat berries which weigh about 4.25 ounces.  Using our field data we estimate we will need to harvest about 3.5 square feet of wheat every day (we assume we will achieve our best field yields).  Since wheat takes about 60 days to mature, we will need to have 210 square feet devoted to wheat.  We are now left with 212 square feet.

 

What nutrients are we lacking now?  Here is a short table:

 

 

Vitamin B-12 is a real problem, so we will examine that later.  Sunflower seeds are a good source of vitamin E, calories and also has zinc in it.  We would like to eat an average of 1.3 ounces of sunflower seeds per day.  Currently we are using about a tablespoon per day in oil for cooking (grease pans, add to bread, etc).  Since there are 2 of us, this equals 1/2 tablespoon per day per person.  To produce this we will need about 2.7 ounces of sunflower seeds (Duhon 1985) per day.  To produce our 4 ounces per day of sunflower seeds we will need to plant 157 square feet in sunflowers (calculated from information presented in Jeavons 1995, page 84--assumes maximum yield) {ouch!}.  This leaves us with only 55 square feet of garden space.

 

Calcium is still very low (43% of RDA).  Sodium is also low at 63% of RDA.  Turnips are an excellent food source for us, for they are high yielding and the greens one of the higher vegetables in calcium.  So we will devote 30 square feet to turnips, which we estimate (from our garden data) is capable of producing 2.4 pounds per square foot in 60 days, or an average of 1 pound per day of root plus a cup a day in leaves (we slightly reduced the root productivity due to harvesting the leaves).  We are now left with 25 square feet of garden space (calculated from information presented in Jeavons 1995, page 88--assumes maximum yield).

 

Peanuts are a very versatile crop.  We shall aim to provide 1 ounce per day.  This will likely require the last of our garden space .

 

We do have another food source, to help fill in the missing vitamins and minerals.  We will be raising chickens.  Very few will be to eat, they are primarily used for egg production.  However we expect to be able to eat about 1 chicken per month.  One of the highest sources available to us for vitamin B12 is chicken liver.  One serving of liver has enough vitamin B12 for 12 days!  So we shall add 1/10th serving per day of chicken liver.  We now have enough vitamin B12, but are still short on calcium and sodium.  The chicken will also add 1/3 serving of chicken (one ounce) per day.

 

So, where are we at?  All of the garden space has been used, but we are still short on a few nutrients.  A complete nutritional analysis of the above diet:

 

 

 

Low fats are not a problem; we can ignore them.  The low calcium may not be a serious problem; in people in China who are on a diet that is primarily vegetarian eat only half as much calcium (with no deficiency symptoms) as the US RDA (Walford and Walford, 1994).  This may be due to improved absorption of calcium; on average adults absorb about 30% of the calcium they ingest (Whiney and Rolfes, 1993).  Whiney and Rolfes also state that "The ideal calcium intake for people is difficult to determine…[because] its blood concentration does not reflect calcium status.  Calcium recommendations are therefore arrived at by way of balance studies."  These balance studies give different results depending on who does them, and around the world there is wide variation on recommended daily allowances.  For instance, the RDA for the US is 1300 milligrams, and the world Health Organization (WHO) recommends only 400-500 milligrams/day.  Therefore, though lower than the US recommendations, we are above the WHO recommendation so we shall accept our low calcium, though a careful watch on bone density is desired (note: in relation to my non-biosphere diet, my calcium intake actually increases).

 

Zinc is very poorly absorbed, with 60 to 85 percent of that consumed passing through and being eliminated.  Fiber inhibits zinc absorption; this may be a problem since the diet is very high in fiber.  In setting the zinc RDA, they assume only 20% are absorbed.  This may actually reflect a value that is lower than we need due to the large quantity of fiber in the diet.  However we may be able to supplement simply by increasing the amount of zinc in the soil, for vegetables vary in zinc content depending on the zinc content of the soil they were grown in.  So, based on this, the addition of a small amount of zinc to the soil of a biosphere is recommended, as is watching for deficiency problems.  These symptoms include blood: high ammonia, low alkaline phosphatase, low insulin; bones: growth retardations, abnormal collagen synthesis; cells/metabolism: slow DNA synthesis, impaired cell division and protein synthesis; digestive system: weak sense of smell, poor sensitivity to the taste of salt, weight loss, delayed glucose absorption, diarrhea, nausea, impaired folate absorption; eyes: night blindness; glandular system: delayed onset of puberty, small gonads in males, decreased synthesis and release of testosterone, abnormal glucose tolerance, reduced synthesis of adrenocortical hormones, altered thyroid function; immune system: altered skin test responses, low white blood cell count, few anti-body forming cells, thymus atrophy, susceptibility to infection; liver/spleen: enlargement; nervous/muscular systems: anorexia (poor appetite), mental lethargy, irritability; reproductive system: low sperm counts; skin: generalized hair loss; lesions; rough, dry appearance, slow healing of wounds and burns (Whiney and Rolfes, 1993).  Should any of these symptoms appear a doctor's visit is needed.  To prevent deficiency supplements may be needed.

 

Sodium has no specific RDA, mostly because diets are so rarely lacking in it.  The Committee on Dietary Allowances estimates the minimum sodium requirements for adults to be 500 milligrams.  This estimate is only slightly higher than the amount in our diet.  By using blood products from the chickens it should be easy to boost the diet to the minimum estimated RDA. 

 

This has been a first pass through the possibilities.  A number of important foods were left out; further analysis should include them.  For example soybeans, brassicas, parsnips, onions, etc.  A second pass will be done at a later date; we know that we will need to plant the initial garden and can proceed at a later date with refining the nutrient and plant balance.

 

We shall now make a second attempt to design a diet that maximizes nutrition (including calories) while minimizing garden space.

 

Parsnips are the most area efficient vegetable you can grow (Duhon 1985).  So let us start with 1 serving per day of parsnips (1/2 cup or 67 grams--1.5 pounds).  To grow half a cup per day we will need

 

 

 

 

Soybeans are a versatile food that is high in calcium.  Add 1 cup of soybeans per day, which gets us to 93% of RDA for calcium, and 98% RDA for sodium.  To get our 1 cup per day we will need 336 square feet (calculated from information presented in Jeavons 1995, page 88--assumes maximum yield) continuously planted in soybeans {ouch!}.

 

Brassicas are excellent vegetables.  For variety we should include a number of them in our diet.  About 1/4 serving per day of broccoli, cabbage, cauliflower and kohlrabi.  8 square feet should be sufficient to provide a continuous supply of these (calculated from information presented in Jeavons 1995, page 80--assumes medium yield).

 

Parsnips are the most area efficient vegetable you can grow (Duhon 1985).  So let us add 1/2 serving per day of parsnips (1/4 cup).

 

Onions are another very efficient crop you can grow (Duhon 1985).  One serving per day (1/2 cup).

 

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