Nutrients must somehow be included in the diet as food or as a nutritional supplement each day. Nutritional needs are not the same for each individual. This depends on a variety of factors. These may include age, sex, weight, nutritional status, physical fitness, pregnancy, convalescence, and so forth. Nutrients must be in a form that is easy to assimilate, even when a given nutrient is taken in amounts larger than what is recommended. If the nutrient cannot be assimilated (or even assimilated efficiently) because of its form, a deficiency will eventually occur. A problem in absorption may also result. Here, the individual's body may act as the "culprit" more so than the nutrient's form. This can be exemplified in the case of malabsorption. In malabsorption of fats, for example, fats (lipids) are hindered from being used by the body. This usually results in a deficiency in fatty acids and/or fat-soluble substances, such as essential fatty acids (linoleic, linolenic, and arachidonic acids), and fat-soluble vitamins (vitamins A, D, E and K).
Various substances, (including chemical agents) may rob our bodies of needed nutrients. Cigarette smokers are at greater risk of suffering from a nutrient deficiency. Since cigarette smoke depletes the body of vitamin C, a smoker may have to consume more vitamin C than a person who does not smoke, with everything else being equal. Alcohol can deplete the body of many of the B vitamins, and antibiotics have the capability of inhibiting the intestinal microflora from synthesizing the body's vitamin K, vitamin B12, and folic acid.
Stress can deplete the body of vitamin C, glucose, minerals, water and many of the B vitamins. Sweating causes the body to lose many kinds of electrolytes including potassium, chloride, and sodium. Illnesses such as cancer and diabetes mellitus can lead to a decrease in nutrients. Cancer can cause a decrease in vitamin C, calcium, protein and iron. Diabetes increases the body's need for chromium, as well as many other nutrients involved in blood sugar regulation.
Upon careful analysis, some 60-70 different minerals have been found in our bodies. These minerals are used to biosynthesize other nutrients, serve as coenzymes (Mg, Mn, and Fe), act as electrolytes (potassium, sodium, and chlorine), and function as cofactors for vitamins (e.g. iron). Vitamins play a variety of other roles as well. They are necessary for the growth of the body (vitamin A), for protection from pollutants (vitamin C), for protection from oxidation (vitamins A, C and E), to function as endocrine hormones (vitamin D), to function in the process of blood coagulation (vitamin K), to aid in the maintenance of a healthy pregnancy (folic acid, vitamin B12, and vitamin A) and so forth.
Carbohydrates are responsible for providing energy in the form of glucose (for the brain, glucose-6- phosphate). In animals (including humans), glucose is stored in a form of "animal starch" (glycogen). This starch is biosynthesized, as well as stored in the liver and in skeletal muscles. Glucose can also be formed from amino acids and glycerol, by a process called gluconeogenesis (the production of glucose from non-carbohydrate sources).
In diabetes mellitus, cells starve to death because insulin (the pancreatic hormone responsible for blood sugar uptake) is not being secreted efficiently, or it is not secreted at all. Since humans lack the enzyme responsible for the breakdown of cellulose (as an energy source), cellulose serves as fiber in humans. Fiber facilitates the expulsion of feces from the alimentary canal. This in turn decreases the chances of harm being caused by fecal toxins and substances.
Proteins constitute a huge proportion of the dry mass in humans, as well as in animals. They have a variety of roles. They act as biological catalysts (enzymes, e.g. glycogen syntheses), transport substances (globins), protection (immunoglobulins), structure (elastin), hormones (insulin), storage (casein), and as chemical messengers. Proteins are necessary for the repair of damaged tissues, and can be used as energy sources when needed. Amino acids, which are the building blocks of proteins, play a role in cell recognition, which is how cells communicate with each other. Nonessential amino acids need not be present in the diet (or as a supplement), because the body can biosynthesize them. When the body needs to biosynthesize protein, all of the amino acids must be present. If even one amino acid is missing, the specific protein cannot (and will not) be synthesized.