Monday, March 5, 2012

Sustainable Nutrition

by Richard Crews
Imagine an isolated colony of 1,000 people cut off from outside food sources (on an island or a space station, for example). Can they provide themselves with an interesting and healthy diet in a sustainable way? In other words, what are their nutritional requirements, and how can they be met without importing (or exporting) food?

Nutritional components are commonly thought of in two groups: "macro-nutrients" and "micro-nutrients."

"Macro" means "large." Macro-nutrients are needed in relatively large amounts (tens of grams or several ounces each day) because they are consumed, that is, used up or destroyed in keeping our metabolic processes going. There are three kinds of macro-nutrients--
(1) Lipids (the chemical name for fats and oils) that are mostly used for energy storage; there are a couple of dozen different kinds of lipids that the body uses,
(2) Carbohydrates (sugars and starches) that are mostly used for generating energy on a cell-by-cell basis; there are also a couple of dozen different kinds of carbohydrates, and
(3) Proteins, a very different story from lipids and carbohydrates; proteins are used in millions of different forms for building and repairing tissues, for enzymes that make the body's chemical reactions go, for reproduction, for digestion . . . in short, for every function, large and small, that the body does; there are many millions of different kinds of proteins.

"Micro" means "small." Micro-nutrients are needed in relatively small amounts (a few milligrams each day, amounts that would fit on the head of a pin) because they are mainly catalysts or helper molecules that are recycled and reused over and over again. However, very small amounts are lost, used up, or destroyed by mistake, as it were, so the the body must take in tiny quantities in order to keep its processes going. But the quantities of micro-nutrients that are needed are generally about 1/1000 of the amounts of macro-nutrients. There are two general kinds of micro-nutrients--vitamins and minerals.

In addition to macro-nutrients and micro-nutrients, the body needs thee other inputs--
(1) Oxygen breathed in from the air, to burn the body's fuels,
(2) Water to dissolve the nutrient chemicals so that they inter-react well, and to lubricate everything, and
(3) Roughage, which is indigestible bulk to carry the foodstuffs through the digestive track.
Although oxygen, water, and roughage are essential for healthy body functioning, they are rather different from the other nutrients and are commonly not considered in an assessment of dietary needs. Suffice it to say that to remain healthy a person needs to--
(1) keep breathing, taking in oxygen day and night,
(2) drink several liters (quarts) of clean, fresh water every day, and
(3) have enough indigestible fiber in the diet (mostly from fruits and vegetables) to keep materials in the digestive track moving along smoothly.

For reasons that are too complicated and interwoven to go into here, the challenges of providing adequate nutrition for an isolated colony boil down to two: providing adequate calories and protein. The other nutritional requirements are met en passant, that is, they are taken in automatically with a healthy, varied diet that includes adequate calories and protein, so they do not need to be considered separately.

(1) Adequate CALORIES for fuel--a person of average size and activity in a subtropical environment needs about 2,000 Calories per day. (Note that nutritional "Calories" are written with a capital "C" to distinguish them from the chemist's "calories," written with a small "c"; one C = 1,000 c.) Individual caloric requirements actually vary widely; a large person doing heavy labor in a cold environment (the Arctic lumberjack scenario) may need 7,000 or 8,000 Calories per day, whereas a small, inactive person may require less than 1,000. But 2,000 Calories per person per day is a useful average. The colony as a whole therefore requires about 7.3 x 10^8 Calories per year.

(2) Adequate amounts of good quality PROTEIN--an average person with a normal range of daily activities needs about 40 grams of protein per day. A person with tissue damage, healing, or growth may need two or three times that much. The colony as a whole therefore requires about 1.5 x 10^7 grams of protein per year.

The stipulation of "good quality" protein refers to the fact that proteins are made up of amino acids. The digestive system breaks up incoming proteins and then the various parts of the body stack those amino acids back together to make the particular proteins that are needed. Some protein sources, such as egg whites and fish, have pretty much all the amino acids the body needs and also have them in good proportions. These are called "good quality" or "complete" proteins. Other food sources, such as beans and nuts, may have a lot of protein, but lack in sufficient amounts of one or more amino acids, so that they are not as useful for the body's purposes.

Most of the colony's caloric needs can be conveniently provided by three crops which are easy to cultivate: wheat, corn, and potatoes. Wheat can be expected to yield about 6 million Calories per acre; corn, about 12; and potatoes, about 18. To provide for about 70% of the colonists' caloric needs from these three crops, it would be necessary to cultivate 25 acres of wheat, 15 acres of corn, and 10 acres of potatoes. These would be irrigated, but fertilized only with compost or natural, non-chemical, fertilizers.

A garden of 10 acres would provide tomatoes, squash, beans, and other fresh vegetables. These would be irrigated, and fertilized with compost. They would be fresh in season, and sun-dried for energy-zero storage to be reconstituted with water for use throughout the year. The garden would also provide a variety of lettuces, cabbages, and leafy greens throughout the year.

Any of these crops could be grown in a hydroponics tank, which is a simple technology although it does require the tanks and irrigation equipment. Farming hydroponically reduces the area requirements by a factor of 6x to 10x.

In addition the colony would have a small orchard of about 250 fruit and nut trees providing almonds, walnuts, apples, plums, peaches, citrus fruit, etc. An average fruit tree can be expected to produce 200 to 400 pounds of fruit per year. These would be fresh in season, and sun-dried for energy-zero storage for use throughout the year. The nuts could be pressed for cooking oils, and for nutritious, high-protein mash for cooking or to feed the chickens. The garden and orchard together provide for about 5% of the colony's caloric needs.

The best sources of protein are fish, eggs, milk, nuts, and beans. Consider egg production, for example: a modest flock of 250 chickens could produce 500 kg of protein per year as eggs. This is about 5% of the colony's protein needs. The chickens eat table scraps and compost, and require little maintenance. The flock is self-sustaining. About 1/10 of the eggs are allowed to hatch to replenish the flock. Most of the little roosters, when they are about three months old, and the hens that are past their laying prime of 3-4 years provide Sunday dining treats.

Fish such as trout, salmon, and tilapia can be grown in tanks or ponds. Fish are a tasty source of high-quality protein.

The various sources of protein also provide calories. Together they provide for about 20% of the colony's caloric needs.

Oils for cooking can be extracted from fish, corn, seeds (particularly melon and squash seeds), and nuts. The orchard could even have a few olive trees for oil production. Olive varieties have been bred to thrive under a wide variety of climate conditions.

Honey bees are easy to maintain, pollinate the crops, and provide 100 to 150 kg (200 to 300 pounds) of honey per hive per year. This can be used to sweeten food or fermented to an alcoholic wine-like beverage called "mead." The bees also provide beeswax that can be used to make candles or soap.

The oils and honey do not add significantly to the colony's calorie provisions. These are met (as outlined above) by the grains (70%), fruits and vegetables (5%), and protein sources (20%).

It appears, on rough analysis, that the nutritional needs of an isolated colony of 1,000 people could be met on a self-sustaining basis (with no input or output exchange with the broader world) with the careful management of less than 100 acres.