Nutrition is the science that explains the interactivity of nutrients and other substances in food in relation to maintenance, growth, reproduction, health and disease of an individual. It includes food intake, assimilation, biosynthesis, catabolism and excretion.  

The diet of an individual is what he/she eats, which is largely determined by the availability and palatability of food stuff. A healthy diet includes the integration of food stuff enriched in nutrients required for the well-being of humans; food preparation and storage methods that preserve nutrients from oxidation, heat or leaching, and that reduces risk of foodborne diseases and illnesses. 

 Unhealthy diet can cause deficiency-related diseases, life threatening complications and chronic systemic diseases and illnesses; this includes anemia, blindness, scurvy, stillbirth, preterm birth, obesity and metabolic syndrome, common chronic systemic diseases such as cardiovascular disease, diabetes, and osteoporosis.

 Undernutrition can lead to body wasting during the acute phase but eventually to malnutrition in chronic phase for example in case of marasmus.

According to the best research evidence, the food we eat has a significant impact on our health. Healthy dietary helps prevent or control many health problems, including obesity, diabetes and certain risk factors for cancer and heart disease, pre and post-natal complications  as well as help prevent or control a varied number of musculoskeletal conditions in infants and adults.

 Scientific studies suggest there are two types of nutrients required by the human body: macro-nutrients which are needed in relatively large quantities, and micronutrients which are needed in smaller quantities. Dietary fiber,a type of carbohydrate, i.e. non-digestible material such as cellulose, is required for both mechanical and biochemical reasons.Some nutrients can be stored, for example the fat-soluble vitamins,while others are required more or less continuously.

Poor health can be caused by a lack of required nutrients, or for some minerals and vitamins, too much of a required nutrient is also a problem to your body.


The macronutrients are Carbohydrates, fiber, protein, fats and water 

The macronutrients (excluding water and fiber) provide structural material (amino acids from which proteins are built, and lipids from which cell membranes and some signaling molecules are built) and energy. Some of the structural material can be used to generate energy internally, and in either case it is measured in Joules or kilocalories. Carbohydrates and proteins provide 17 kJ approximately (4 kcal) of energy per gram, while fats provide 37 kJ (9 kcal) per gram, although the net energy from either depends on factors such as absorption and digestive effort, which may vary occasionally. Vitamins, minerals, fiber, and water do not provide energy, but are required for other reasons.


Carbohydrates may be classified as monosaccharides, disaccharides and polysaccharides depending on the number of monomer (sugar) units they contain. They constitute a large part of foods such as rice, bread, noodles and other grain-based products, such as maize, millet sorghum also potatoes, yams, beans, fruits, fruit juices and vegetables.

 Monosaccharides, disaccharides, and polysaccharides contain one, two, and three or more sugar units, respectively. Polysaccharides (starch) are often referred to as complex carbohydrates because they are typically long, multiple branched chains of sugar units.


Dietary fiber is a carbohydrate that is incompletely absorbed in humans and in some animals. Like all carbohydrates, when it is metabolized it can produce four Calories (kilocalories) of energy per gram. However, in most circumstances it accounts for less than that because of its limited absorption and digestibility. Dietary fiber consists mainly of cellulose, a large carbohydrate polymer which is indigestible as humans do not have the required enzymes to disassemble it.

There are two fiber subcategories: soluble and insoluble fiber.

Soluble fiber is found in whole grains, fruits (especially prunes, plums and figs), and vegetables are good sources of dietary fiber. There are many health benefits of a high-fiber diet. Dietary fiber helps reduce the chance of gastrointestinal problems such as constipation and diarrhea by increasing the weight and size of stool and softening it. Insoluble fiber, found in whole wheat flour, nuts and vegetables, especially stimulates peristalsis. The involuntary rhythmic muscular contractions of the intestines which move, digest along the digestive tract. Soluble fiber, found in oats, peas, beans, and many fruits, dissolves in water in the intestinal tract to produce a gel that slows the movement of food through the intestines. This may help lower blood glucose levels because it can slow the absorption of sugar. Additionally, fiber, perhaps especially that from whole grains, is thought to possibly help lessen insulin spikes, and therefore reduce the risk of type 2 diabetes.


Proteins are structural materials in much of the animal body (e.g. muscles, skin, and hair). They also form the enzymes that control chemical reactions throughout the body. Each protein molecule is composed of amino acids, which are distinguished by inclusion of nitrogen and sometimes Sulphur (these components are responsible for the distinctive smell of burning protein, such as the keratin in hair). The body requires amino acids to produce new proteins (protein retention) and to replace damaged proteins (maintenance). As there is no protein or amino acid storage provision, amino acids must be present in the diet. Excess amino acids are discarded, typically in the urine. For all animals, some amino acids are essential (an animal cannot produce them internally) and some are non-essential (the animal can produce them from other nitrogen-containing compounds). About twenty amino acids are found in the human body, and about ten of these are essential and, therefore, must be included in the diet.

 A diet that contains adequate amounts of amino acids (especially those that are essential) is particularly important in situations like; during early development and maturation, pregnancy, lactation, or injury (a burn, for instance). A complete protein source contains all the essential amino acids while an incomplete protein source lacks one or more of the essential amino acids.

It is possible to combine two incomplete protein sources e.g., rice and beans, to make a complete protein source. Characteristic combinations are the basis of definite and different cultural cooking traditions. Complementary sources of protein do not need to be eaten in the same meal as they are used together with the body excess amino acids from protein and can be converted into glucose and used for fuel through a process called gluconeogenesis .


A molecule of dietary fat typically consists of several fatty acids (containing long chains of carbon and hydrogen atoms), bonded to a glycerol. They are typically found as triglycerides (three fatty acids attached to one glycerol backbone).

Fats may be classified as saturated or unsaturated basing on the detailed structure of the fatty acids involved. Saturated fats have all of the carbon atoms in their fatty acid chains bonded to hydrogen atoms, whereas unsaturated fats have some of these carbon atoms double- bonded, their molecules have relatively fewer hydrogen atoms than a saturated fatty acid of the same length. Unsaturated fats may be further classified as monounsaturated (one double-bond) or polyunsaturated (many double-bonds). Furthermore, depending on the location of the double-bond in the fatty acid chain, unsaturated fatty acids are classified as omega-3 or omega-6 fatty acids. The trans fats are a type of unsaturated fat with trans-isomer bonds; these are rare in nature and in foods from natural sources; they are typically created in an industrial process called hydrogenation There are nine kilocalories in each gram of fat. Fatty acids such as conjugated linoleic acid, eleostearic acid, catalpic acid, and punicc acid, other than providing energy, represent potent immune modulatory molecules.

Saturated fats (typically from animal sources) have been a staple in many world cultures for millennia. Unsaturated fats (e. g., vegetable oil) are considered healthier, while Trans fats are to be avoided. Saturated and some Trans fats are typically solid at room temperature (such as butter or lard), unsaturated fats are typically liquids (such as olive oil or flaxseed oil).Trans fats are very rare in nature, and have been shown to be highly detrimental to human health, but have properties useful in the food processing industry, such as rancidity resistance.

Most fatty acids are non-essential, meaning that the body can produce them as needed, generally from other fatty acids and always by disbursing energy to do so. For humans, at least two fatty acids are essential and must be included in the diet. Appropriate balance of essential fatty acids i.e.  Omega-3 and omega-6 is important for health. Both of these "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins, which have roles throughout the human body. They are hormones, in some respects. The omega-3 eicosapentaenoic acid (EPA), which can be made in the human body from the omega-3 essential fatty acid alpha-linolenic acid (ALA), or taken in through marine food sources, serves as a building block for series 3 prostaglandins (e.g., weakly inflammatory PGE3). The omega-6 dihomo-gamma-linolenic acid (DGLA) serves as a building block for series 1 prostaglandins (e.g. anti-inflammatory PGE1), whereas arachidonic acid (AA) serves as a building block for series 2 prostaglandins (e.g. pro-inflammatory PGE 2). Both DGLA and AA can be made from the omega-6 linoleic (LA) in the human body, or can be taken in directly through food. An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different prostaglandins, which is one reason why a balance between omega-3 and omega-6 is believed important for cardiovascular health. In industrialized societies, people typically consume large quantities of processed vegetable oils, which have reduced amounts of the essential fatty acids along with too much of omega-6 fatty acids relative to omega-3 fatty acids.


Water is essential for chemical processes to partake in human body and it constitutes the highest percentage in body cells, tissues and even blood which plays a key role in nourishment of the entire body systems 

Early recommendations for the amount of water required for maintenance of good health suggested that 6–8 glasses of water daily is the minimum to maintain the proper state of body hydration. However, the notion that a person should consume eight glasses of water per day cannot be traced to a credible scientific source.

Water is rid off from the body in multiple forms; including water vapour in exhaled breath, sweating, urine and feces. It is therefore, necessary and most importantly to adequately rehydrate to replace lost fluids from the body systems as water plays a vital role for the well-being and systems operation. 


Pure ethanol provides calories per gram. Wine and beer contain a similar range of ethanol for servings of 5 ounces and 12 ounces, respectively, but these beverages also contain non-ethanol calories. A 5 ounce serving of wine contains 100 to 130 calories. A 12 ounce serving of beer contains 95 to 200 calories. Alcoholic beverages are considered empty calories foods because other than calories, these contribute no essential nutrients.


The micronutrients include: - Vitamins and Minerals (macro-minerals and trace minerals)


Dietary minerals are inorganic chemical elements required by living organisms, the four elements which includes oxygen, carbon, hydrogen and nitrogen, are present in nearly all organic molecules. The term "mineral" is archaic, since the intent is to describe simply the less common elements in the diet. Some are heavier than the four just mentioned, including several metals, which often occur as ions in the body.  Dietitians recommend that these be supplied from foods in which they occur naturally or at least as complex compounds, or sometimes even from natural inorganic sources (such as calcium carbonate from ground oyster shells). Some minerals are absorbed much more readily in the ionic forms found in such sources. Also, minerals are often artificially added to the diet as supplements; the most famous is likely iodine in iodized salt which helps to prevents goiter


Many elements are essential nutrients known as dietary minerals. Some have cofactors roles while others are electrolytes. Below are Elements with recommended dietary allowance greater than 150 mg/day.

·         Calcium, a common electrolyte, and needed structurally (for muscle and digestive system health, bone strength, in some forms neutralize acidity, provides signaling ions for nerve and membrane functions)

·         Phosphorus, required component for building of bones; essential for energy processing

·         Chloride; electrolyte

·         Magnesium, required for processing ATP and related reactions. Builds bone, and facilitates peristalsis.

·         Potassium, an electrolyte (essential for heart and nerve functions)

·         Sodium, an electrolyte; common in food and manufactured beverages, as sodium chloride. Excessive intake of sodium chloride can deplete calcium and magnesium which might lead to high blood pressure.

Trace minerals

Many elements are required in trace amounts; generally, because they play a catalytic role in enzyme activities. Some trace mineral elements are with recommended dietary allowances of < 200 mg/day are listed below.

·         Cobalt required for biosynthesis of vitamin B12 family of coenzymes. Animals cannot biosynthesize B12, and must obtain this cobalt-containing vitamin in their diet.

·         Copper required component of many redox enzymes, including cytochrome c oxidase Chromium is required for sugar metabolism

·         Iodine required not only for the biosynthesis of thyroxine but it is used for other important organs as breast, stomach, salivary glands, thymus, etc. for this reason iodine is needed in larger quantities than others in this list.

·         Iron is required for many enzymes, and for hemoglobin and some other proteins in the body

·         Manganese is needed for processing of oxygen

·         Molybdenum is required for xanthine oxidase and related oxidases

·         Selenium is required for peroxidase (antioxidant proteins)


Vitamins are essential nutrients for the human body necessary in the diet for good health. Vitamin deficiencies may result in disease conditions, such as scurvy osteoporosis goiter, impaired immune system, disorders of cell metabolism, certain forms of cancer, and symptoms of premature aging, mental health problems, and many others. Excess levels of some vitamins are also risky to health. The Food and Nutrition Board of the Institute of Medicine has established Tolerable Upper Intake Levels for seven vitamins.

(Vitamin D is an exception as the body can synthesize in the skin in the presence of UVB radiation).


Phytochemicals for example polyphenols are compounds produced naturally in plants (in Greek phyto means "plant"). Generally, the term associates compounds that are prevalent in plant foods, but are not proven to be essential for human nutrition, as of 2018. There is no conclusive evidence in humans that polyphenols or other non-nutrient compounds from plants confabulate health benefits, mainly because these compounds have indigent bioavailability i.e., following ingestion, they are digested into smaller metabolites with unknown functions, then are quickly eliminated from the body

The initial studies sought to reveal if dietary supplements might promote health, one meta-analysis concluded that supplementation with antioxidant vitamins A and E and beta-carotene did not convey any benefits, and may increase risk of death. Vitamin C and selenium supplements did not impact mortality rate. Health effects of non-nutrient phytochemicals such as polyphenols were not assessed in this review.



In humans, there four dominant phyla, this includes Firmicutes, Bacteroidetes, Actinobacteria and Proteobacteria. They are essential to digestion and are also affected by food that is consumed. Bacteria in the large intestine perform many important functions for humans, including breaking down and aiding in the absorption of fermentable fiber, stimulating cell growth, repressing the growth of harmful bacteria, training the immune system to respond only to pathogens, producing vitamin B12 and defending against some infectious diseases. Probiotics refers to the idea of deliberately consuming live bacteria in an attempt to change the bacterial population in the large intestine, to the health benefit of the host human or animal. Prebiotic refers to the idea that consuming a bacterial energy source such as soluble fiber could support the population of health-beneficial bacteria in the large intestine. There is not yet a scientific consensus as to health benefits accruing from probiotics or prebiotics.