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Another important requirement is that of nitrogen. Protein catabolism provides a source of organic nitrogen. Amino acids are the building blocks of proteins and protein breakdown provides amino acids that are used for cellular function. The carbon and nitrogen derived from these become the building block for nucleotides, nucleic acids, proteins, cells, and tissues. Excess nitrogen must be excreted as it is toxic. Fats add flavor to food and promote a sense of satiety or fullness. Fatty foods are also significant sources of energy because one gram of fat contains nine calories. Fats are required in the diet to aid the absorption of fat-soluble vitamins and the production of fat-soluble hormones.
While the animal body can synthesize many of the molecules required for function from the organic precursors, there are some nutrients that need to be consumed from food. These nutrients are termed essential nutrients , meaning they must be eaten, and the body cannot produce them.
The omega-3 alpha-linolenic acid and the omega-6 linoleic acid are essential fatty acids needed to make some membrane phospholipids. Vitamins are another class of essential organic molecules that are required in small quantities for many enzymes to function and, for this reason, are considered to be co-enzymes. Absence or low levels of vitamins can have a dramatic effect on health, as outlined in [link] and [link] . Both fat-soluble and water-soluble vitamins must be obtained from food. Minerals , listed in [link] , are inorganic essential nutrients that must be obtained from food. Among their many functions, minerals help in structure and regulation and are considered co-factors. Certain amino acids also must be procured from food and cannot be synthesized by the body. These amino acids are the “essential” amino acids. The human body can synthesize only 11 of the 20 required amino acids; the rest must be obtained from food. The essential amino acids are listed in [link] .
| Water-soluble Essential Vitamins | |||
|---|---|---|---|
| Vitamin | Function | Deficiencies Can Lead To | Sources |
| Vitamin B 1 (Thiamine) | Needed by the body to process lipids, proteins, and carbohydrates Coenzyme removes CO 2 from organic compounds | Muscle weakness, Beriberi: reduced heart function, CNS problems | Milk, meat, dried beans, whole grains |
| Vitamin B 2 (Riboflavin) | Takes an active role in metabolism, aiding in the conversion of food to energy (FAD and FMN) | Cracks or sores on the outer surface of the lips (cheliosis); inflammation and redness of the tongue; moist, scaly skin inflammation (seborrheic dermatitis) | Meat, eggs, enriched grains, vegetables |
| Vitamin B 3 (Niacin) | Used by the body to release energy from carbohydrates and to process alcohol; required for the synthesis of sex hormones; component of coenzyme NAD + and NADP + | Pellagra, which can result in dermatitis, diarrhea, dementia, and death | Meat, eggs, grains, nuts, potatoes |
| Vitamin B 5 (Pantothenic acid) | Assists in producing energy from foods (lipids, in particular); component of coenzyme A | Fatigue, poor coordination, retarded growth, numbness, tingling of hands and feet | Meat, whole grains, milk, fruits, vegetables |
| Vitamin B 6 (Pyridoxine) | The principal vitamin for processing amino acids and lipids; also helps convert nutrients into energy | Irritability, depression, confusion, mouth sores or ulcers, anemia, muscular twitching | Meat, dairy products, whole grains, orange juice |
| Vitamin B 7 (Biotin) | Used in energy and amino acid metabolism, fat synthesis, and fat breakdown; helps the body use blood sugar | Hair loss, dermatitis, depression, numbness and tingling in the extremities; neuromuscular disorders | Meat, eggs, legumes and other vegetables |
| Vitamin B 9 (Folic acid) | Assists the normal development of cells, especially during fetal development; helps metabolize nucleic and amino acids | Deficiency during pregnancy is associated with birth defects, such as neural tube defects and anemia | Leafy green vegetables, whole wheat, fruits, nuts, legumes |
| Vitamin B 12 (Cobalamin) | Maintains healthy nervous system and assists with blood cell formation; coenzyme in nucleic acid metabolism | Anemia, neurological disorders, numbness, loss of balance | Meat, eggs, animal products |
| Vitamin C (Ascorbic acid) | Helps maintain connective tissue: bone, cartilage, and dentin; boosts the immune system | Scurvy, which results in bleeding, hair and tooth loss; joint pain and swelling; delayed wound healing | Citrus fruits, broccoli, tomatoes, red sweet bell peppers |
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