I am assuming that carbon life forms on other planets will have metabolisms similar to animals here. This may not be true, but our life forms work! Certainly all life forms need energy in order to live and reproduce.
The experts here seem to agree that the following values hold:
1 gram of protein = 4 Kilocalories (food calories)
1 gram of carbohydrate = 4 Kilocalories
1 gram of fat = 9 Kilocalories
One ounce = 28.3 grams. Let's multiply and get an estimate that is easy to work with.
Translating the food values to ounces we get;
1 ounce of protein = (28.3 * 4 = 113.2) about 100 Kilocalories
1 ounce of carbohydrate = (28.3 * 4 = 113.2) about 100 Kilocalories
1 ounce of fat = (28.3 * 9 = 254.7) about 250 Kilocalories
In general, meat is protein, plants are carbohydrates. Meat (protein) builds animal bodies: carbohydrates provide energy for moving, breathing, digestion, etc. If an animal eats only meat, it will burn some of the protein for energy.
Foods are usually made up of a mixture of components: carbohydrates, proteins, fat, roughage (indigestible things like stalks, hair, feathers, etc) minerals, vitamins, and so on. For this project we will assume that the minerals and vitamins work out all right in the foods that our aliens eat.
Scientists use the metric system, so I have given you information in that format as well as in pounds and ounces. Begin by using measurements that make sense to you so that you can think about what you are doing.
1000 grams = 1 Kilogram
one ounce = 28.3 grams
(I have been using ounces times 30 = grams to get approximate values)
The stated caloric values of foods vary, so for this project I am picking the following values. These are from pages for human dieters. I have rounded off the numbers to simplify the math.
Notice that some of the plants have a very low caloric content per ounce. This is because plant tissues may contain up to 90% water.
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