Nutrition is the science of how nutrients fuel and support the necessary biological functions of a living creature. It includes food intake, absorption, assimilation, biosynthesis, catabolism and excretion.
The most well known lifeforms are carbon based life who consume mainly organic compounds sources of food energy for the body.
The macronutrients (excluding fiber and water) provide structural material (amino acids from which proteins are built, and lipids from which cell membranes and some signaling molecules are built) and energy.
Proteins are one of the building blocks of body tissue, and can also serve as a fuel source. Aside from water, proteins are the most abundant kind of molecules in an organic body. Protein can be found in all cells of the body and is the major structural component of all cells in the body, especially muscle but also organs and skin. They also serve as enzymes; which catalyze all of the reactions of metabolism; regulatory proteins, such as transcription factors or cyclins that regulate the cell cycle; signaling molecules or their receptors such as some hormones and their receptors; defensive proteins, which can include everything from antibodies of the immune system, to toxins.
Proteins are polymer chains made of amino acids linked together by peptide bonds. During digestion, proteins are broken down into smaller polypeptide chains which is crucial for the synthesis of the essential amino acids that cannot be biosynthesized by the body.
For humanoids and demihumanoids, there are nine essential amino acids which humans must obtain from their diet in order to prevent protein-energy malnutrition and resulting death. They are phenylalanine, valine, threonine,tryptophan, methionine, leucine, isoleucine, lysine, and histidine and found mainly in animal sources like meat, fish, and eggs known as complete proteins. Consuming a mixture of plant-based protein sources like pulses and grains can also provide them.
Carbohydrates are an organism’s source of quick fuel and break down faster than protein and fats. Carbohydrates may be classified as monosaccharides, disaccharides, or polysaccharides depending on the number of monomer (sugar) units they contain. Simple carbs (mono and di) like cane sugar break down faster than complex carbs like grains and starchy vegetables. Glucose is a nearly universal and accessible source of energy for various organisms.
Fiber refers to complex polysaccharides that can’t be digested by the food, like cellulose for humanoids. Although it doesn’t provide energy, fiber adds bulk to the diet and improves the process of transporting foods through the digestive tract and is helpful for controlling blood sugar levels.
Fats are also a source of fuel for the body that are digested into fatty acids and glycerol. As they take the longest of macromolecules to digest, they serve to store energy and provide the body with sustained energy. Saturated fats are derived mainly from animal sources and unsaturated fats are derived mainly from plants sources.
Fats are part of large group of molecules called lipids that not only provide energy but serve important biological functions like forming cell membranes and being signaling molecules and hormones. In an organism’s body, fats make up adipose tissue which provides thermal insulation and cushions organs.
Water is a vital nutrient for any organism but is different from proteins, fats, or carbs in that is not a food as it doesn’t provide energy. Instead it performs vital functions in the body like facilitating food digestion, helps with waste excretion, transporting nutrients to the cells, maintaining a stable body temperature, providing protection for numerous body components, lubricating joints so they can function properly, a solvent for solutes, and an essential part of many metabolic processes within the body.
Micronutrients are required for the proper functioning of the organic body. They do not provide fuel sources as foods do, but they are important components of various biochemical processes. Most vitamins and minerals cannot be made within the body and must be consumed through diet or supplementation.
Dietary minerals are inorganic chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen that are present in nearly all organic molecules. Some are structural, but many play a role as electrolytes or play a catalytic role in enzymes.
Vitamins are recognized as organic essential nutrients, necessary in the diet for good health and have diverse biochemical functions.
Live Constructs have a variety of ways to obtain the structural substances needed to maintain their forms and have a variety of ways to obtain energy.
Anthroids gain their nutrients and energy from separate sources, energy comes either from electrical voltage or chemical engines that digest organic molecules for energy like organic beings and partly assimilate them. This species mass in particular is composed of metal and plastic polymers which they replace either by building and replacing their body parts manually or by mimicking organic beings by ingesting metallic & plastic sources into their compartments and assimilating them as nutrients.
Spirits that manifest as live constructs typically keep the same energy source as other spirits but have to feed on whatever substance their constructs are composed of to grow and replace mass lost through metabolic processes.
Spirits get their nutrients from ambient intangible matter which they feed on to assimilate into their structure and grow.
Spirits get their energy from psychic energy which is emanated from the thought processes of sapient beings or from the ambient terrestrial mana of the planet. Spirits can usually convert the two different forms of nutrients as they need, basically breaking down spirit mass into energy or building psychic energy into spirit mass.
When spirits manifest a physical form, their needs change depending on the construct they take. Usually a spirit in an inorganic construct still receives their energy from either abundant mental thoughts or magical energy so they don’t need to eat, drink,
or even breathe in the way that organic lifeforms need to. They can however configure their bodies to mimic the necessary bodily organ systems be able to perform these actions if they want to, though any material they consume will later have to be excreted. They also lack the need for long rest periods like sleep. However, overworking their forms beyond a managable amount causes physical and mental exhaustion that sleeping would best take care of.
Spirits that use an organic construct or are hybrids of a organic species, will require food for nutrition and energy like typical organisms. However, they can adapt to acquiring energy form the same sources as other spirits which could reduce the amount of organic compounds they need for maintaining the structure and metabolic processes of their bodies.
Autotrophs are life forms that make their own food once they absorb the simple substances and a seperate source of energy present in their surroundings.
Plants/cyanobacteria/green algae and most magiflora absorb water, vitamins, minerals and carbon dioxide in environment and with light energy from the sun, they are capable of synthesizing their own organic compounds for food and served as food sources for consumers, they are referred to as producers.
Lithotrophs are life forms that take in inorganic substances to synthesize their biological components or produce energy.
Live constructs are typically lithovores, creatures that have consume mostly inorganic substances to replace their structure due to being made of inorganic compounds as opposed to organic compounds. While they can get energy from breaking down inorganic compounds, most find alternative energy sources that more efficient for biosynthesis.
Heterotrophs are life forms that can not fix inorganic compounds so instead take in organic substances, usually from other organisms, and are able to use all the energy that they obtain from food for growth and reproduction and the matter for structure.
Carnivores are heterotrophs that derive their energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging. Animals that depend solely on animal flesh for their nutrient requirements are called obligate carnivores while those that also consume non-animal food are called facultative carnivores.
Omnivores are heterotrophs that derive their energy and nutrient requirements from a diet consisting of both animal and plant tissues. Often, omnivores also have the ability to incorporate food sources such as algae, fungi, and bacteria into their diet as well.