Nutrition: What is Nutrition and Nutrients

Nutrition, nourishment, or aliment, is the supply of materials - food - required by organisms and cells to stay alive. In science and human medicine, nutrition is the science or practice of consuming and utilizing foods.

In hospitals, nutrition may refer to the food requirements of patients, including nutritional solutions delivered via an IV (intravenous) or IG (intragastric) tube.

Nutritional science studies how the body breaks food down (catabolism) and repairs and creates cells and tissue (anabolism) - catabolism and anabolism = metabolism. Nutritional science also examines how the body responds to food. In other words, "nutritional science investigates the metabolic and physiological responses of the body to diet".

As molecular biology, biochemistry and genetics advance, nutrition has become more focused on the steps of biochemical sequences through which substances inside us and other living organisms are transformed from one form to another - metabolism and metabolic pathways.

Nutrition also focuses on how diseases, conditions and problems can be prevented or lessened with a healthy diet.

Nutrition also involves identifying how certain diseases, conditions or problems may be caused by dietary factors, such as poor diet (malnutrition), food allergies, metabolic diseases, etc.

The human body requires seven major types of nutrients

A nutrient is a source of nourishment, an ingredient in a food, e.g. protein,carbohydrate, fat, vitamin, mineral, fiber and water. Macronutrients are nutrients we need in relatively large quantities. Micronutrients are nutrients we need in relatively small quantities.

Energy macronutrients - these provide energy, which is measured either in kilocalories (kcal) or Joules. 1 kcal = 4185.8 joules.

• Carbohydrates - 4 kcal per gram
• Molecules consist of carbon, hydrogen and oxygen atoms. Carbohydrates include monosaccharides (glucose, fructose, glactose), sisaccharides, and polysaccharides (starch). 
• Nutritionally, polysaccharides are more favored for humans because they are more complex molecular sugar chains and take longer to break down - the more complex a sugar molecule is the longer it takes to break down and absorb into the bloodstream, and the less it spikes blood sugar levels. Spikes in blood sugar levels are linked to heart and vascular diseases.

• Proteins - 4 kcal per gram
• Molecules contain nitrogen, carbon, hydrogen and oxygen. Simple proteins, called monomers, are used to create complicated proteins, called polymers, which build and repair tissue. When used as a fuel the protein needs to break down, as it breaks down it gets rid of nitrogen, which has to be eliminated by the kidneys.

• Fats - 9 kcal per gram
• Molecules consist of carbon, hydrogen, and oxygen atoms. Fats are triglycerides - three molecules of fatty acid combined with a molecule of the alcohol glycerol. Fatty acids are simple compounds (monomers) while triglycerides are complex molecules (polymers). For more details on dietary fat, go to What is fat? How much fat should I eat?

Other macronutrients. 

These do not provide energy

• Fiber
• Fiber consists mostly of carbohydrates. However because of its limited absorption by the body, not much of the sugars and starches get into the blood stream. Fiber is a crucial part of essential human nutrition. 

• Water
• About 70% of the non-fat mass of the human body is water. Nobody is completely sure how much water the human body needs - claims vary from between one to seven liters per day to avoid dehydration. We do know that water requirements are very closely linked to body size, age, environmental temperatures, physical activity, different states of health, and dietary habits. Somebody who consumes a lot of salt will require more water than another person of the same height, age and weight, exposed to the same levels of outside temperatures, and similar levels of physical exertion who consumes less salt. Most blanket claims that 'the more water you drink the healthier your are' are not backed with scientific evidence. The variables that influence water requirements are so vast that accurate advice on water intake would only be valid after evaluating each person individually.

Micronutrients

• Minerals
• Dietary minerals are the other chemical elements our bodies need, apart from carbon, hydrogen, oxygen and nitrogen. The term "minerals" is misleading, and would be more relevant if called "ions" or "dietary ions" (it is a pity they are not called so). People whose intake of foods is varied and well thought out - those with a well balanced diet - will in most cases obtain all their minerals from what they eat. Minerals are often artificially added to some foods to make up for potential dietary shortages and subsequent health problems. The best example of this is iodized salt - iodine is added to prevent iodine deficiency, which even today affects about two billion people and causes mental retardation and thyroid gland problems. Iodine deficiency remains a serious public health problem in over half the planet. 

• Experts say that 16 key minerals are essential for human biochemical processes by serving structural and functional roles, as well as electrolytes: 

• Potassium
• What it does - a systemic (affects entire body) electrolyte, essential in co-regulating ATP (an important carrier of energy in cells in the body, also key in making RNA) with sodium. 
• Deficiency - hypokalemia (can profoundly affect the nervous system and heart). 
• Excess - hyperkalemia (can also profoundly affect the nervous system and heart). 
• Chloride
• What it does - key for hydrochloric acid production in the stomach, also important for cellular pump functions. 
• Deficiency - hypochleremia (low salt levels, which if severe can be very dangerous for health). 
• Excess - hyperchloremia (usually no symptoms, linked to excessive fluid loss). 
• Sodium
• What it does - a systemic electrolyte, and essential in regulating ATP with potassium. 
• Deficiency - hyponatremia (cause cells to malfunction; extremely low sodium can be fatal). 
• Excess - hypernatremia (can also cause cells to malfunction, extremely high levels can be fatal). 
• Calcium
• What it does - important for muscle, heart and digestive health. Builds bone, assists in the synthesis and function of blood cells. 
• Deficiency - hypocalcaemia (muscle cramps, abdominal cramps, spasms, and hyperactive deep tendon reflexes). 
• Excess - hypercalcaemia (muscle weakness, constipation, undermined conduction of electrical impulses in the heart, calcium stones in urinary tract, impaired kidney function, and impaired absorption of iron leading to iron deficiency). 
• Phosphorus
• What it does - component of bones and energy processing. 
• Deficiency - hypophosphatemia, an example is rickets. 
• Excess - hyperphosphatemia, often a result of kidney failure. 
• Magnesium
• What it does - processes ATP and required for good bones. 
• Deficiency - hypomagnesemia (irritability of the nervous system with spasms of the hands and feet, muscular twitching and cramps, and larynx spasms). 
• Excess - hypermagnesemia (nausea, vomiting, impaired breathing, low blood pressure). Very rare, and may occur if patient has renal problems. 
• Zinc
• What it does - required by several enzymes. 
• Deficiency - short stature, anemia, increased pigmentation of skin, enlarged liver and spleen, impaired gonadal function, impaired wound healing, and immune deficiency. 
• Excess - suppresses copper and iron absorption. 
• Iron
• What it does - required for proteins and enzymes, especially hemoglobin. 
• Deficiency - anemia. 
• Excess - iron overload disorder; iron deposits can form in organs, particularly the heart. 
• Manganese
• What it does - a cofactor in enzyme functions. 
• Deficiency - wobbliness, fainting, hearing loss, weak tendons and ligaments. Less commonly, can be cause of diabetes. 
• Excess - interferes with the absorption of dietary iron. 
• Copper
• What it does - component of many redox (reduction and oxidation) enzymes. 
• Deficiency - anemia or pancytopenia (reduction in the number of red and white blood cells, as well as platelets) and a neurodegeneration. 
• Excess - can interfere with body's formation of blood cellular components; in severe cases convulsions, palsy, and insensibility and eventually death (similar to arsenic poisoning). 
• Iodine
• What it does - required for the biosynthesis of thyroxine (a form of thyroid hormone). 
• Deficiency - developmental delays, among other problems. 
• Excess - can affect functioning of thyroid gland. 
• Selenium
• What it does - cofactor essential to activity of antioxidant enzymes. 
• Deficiency - Keshan disease (myocardial necrosis leading to weakening of the heart), Kashing-Beck disease (atrophy degeneration and necrosis of cartilage tissue). 
• Excess - garlic-smelling breath, gastrointestinal disorders, hair loss, sloughing of nails, fatigue, irritability, and neurological damage. 
• Molybdenum
• What it does - vital part of three important enzyme systems, xanthine oxidase, aldehyde oxidase, and sulfite oxidase. It has a vital role in uric acid formation and iron utilization, in carbohydrate metabolism, and sulfite detoxification. 
• Deficiency - may affect metabolism and blood counts, but as this deficiency is often alongside other mineral deficiencies, such as copper, it is hard to say which one was the cause of the health problem. 
• Excess - there is very little data on toxicity, therefore excess is probably not an issue.

• Vitamins
• These are organic compounds we require in tiny amounts. An organic compound is any molecule that contains carbon. It is called a vitamin when our bodies cannot synthesize (produce) enough or any of it. So we have to obtain it from our food. Vitamins are classified by what they do biologically - their biological and chemical activity - and not their structure.

• Vitamins are classified as water soluble (they can dissolve in water) or fat soluble (they can dissolve in fat). For humans there are 4 fat-soluble (A, D, E, and K) and 9 water-soluble (8 B vitamins and vitamin C) vitamins - a total of 13.
• Water soluble vitamins need to be consumed more regularly because they are eliminated faster and are not readily stored. Urinary output is a good predictor of water soluble vitamin consumption. Several water-soluble vitamins are manufactured by bacteria.
• Fat soluble vitamins are absorbed through the intestines with the help of fats (lipids). They are more likely to accumulate in the body because they are harder to eliminate quickly. Excess levels of fat soluble vitamins are more likely than with water-soluble vitamins - this condition is called hypervitaminosis. Patients with cystic fibrosis need to have their levels of fat-soluble vitamins closely monitored.
• We know that most vitamins have many different reactions, which means they have several different functions. Below is a list of vitamins, and some details we know about them:
• Vitamin A
• chemical names - retinol, retinoids and carotenoids.
• Solubility - fat.
• Deficiency disease - Night-blindness.
• Overdose disease - Keratomalacia (degeneration of the cornea).
• Vitamin B1
• chemical name - thiamine.
• Solubility - water.
• Deficiency disease - beriberi, Wernicke-Korsakoff syndrome.
• Overdose disease - rare hypersensitive reactions resembling anaphylactic shock when overdose is due to injection. Drowsiness.

• Vitamin B2
• chemical name - riboflavin
• Solubility - water
• Deficiency disease - ariboflanisosis (mouth lesions, seborrhea, and vascularization of the cornea).
• Overdose disease - no known complications. Excess is excreted in urine.
• Vitamin B3
• chemical name - niacin.
• Solubility - water.
• Deficiency disease - pellagra.
• Overdose disease - liver damage, skin problems, and gastrointestinal complaints, plus other problems.
• Vitamin B5
• chemical name -pantothenic acid.
• Solubility - water.
• Deficiency disease - paresthesia (tingling, pricking, or numbness of the skin with no apparent long-term physical effect).
• Overdose disease - none reported.
• Vitamin B6
• chemical name - pyridoxamine, pyridoxal.
• Solubility - water.
• Deficiency disease - anemia, peripheral neuropathy.
• Overdose disease - nerve damage, proprioception is impaired (ability to sense stimuli within your own body is undermined).
• Vitamin B7
• chemical name - biotin.
• Solubility - water.
• Deficiency disease - dermatitis, enteritis.
• Overdose disease - none reported.
• Vitamin B9
• chemical name - folinic acid.
• Solubility - water.
• Deficiency disease - birth defects during pregnancy, such as neural tube.
• Overdose disease - seizure threshold possibly diminished.
• Vitamin B12
• chemical name - cyanocobalamin, hydroxycobalamin, methylcobalamin.
• Solubility - water.
• Deficiency disease - megaloblastic anemia (red blood cells without nucleus).
• Overdose disease - none reported.
• Vitamin C
• chemical name - ascorbic acid.
• Solubility - water.
• Deficiency disease - scurvy, which can lead to a large number of complications.
• Overdose disease - vitamin C megadosage - diarrhea, nausea, skin irritation, burning upon urination, depletion of the mineral copper, and higher risk of kidney stones.
• Vitamin D
• chemical name - ergocalciferol, cholecalciferol.
• Solubility - fat.
• Deficiency disease - rickets, osteomalacia (softening of bone), recent studies indicate higher risk of some cancers.
• Overdose disease - hypervitaminosis D (headache, weakness, disturbed digestion, increased blood pressure, and tissue calcification).
• Vitamin E
• chemical name - tocotrienols.
• Solubility - fat.
• Deficiency disease - very rare, may include hemolytic anemia in newborn babies.
• Overdose disease - one study reported higher risk of congestive heart failure.
• Vitamin K
• chemical name - phylloquinone, menaquinones.
• Solubility - fat.
• Deficiency disease - greater tendency to bleed.
• Overdose disease - may undermine effects of warfarin.Most foods contain a combination of some, or all of the seven nutrient classes. We require some nutrients regularly, and others less frequently. Poor health may be the result of either not enough or too much of a nutrient, or some nutrients - an imbalance.