Human Nutrition

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Carbohydrates range from simple monosaccharides glucose, fructose and galactose to complex polysaccharides starch. Fats are triglycerides , made of assorted fatty acid monomers bound to a glycerol backbone. Some fatty acids, but not all, are essential in the diet: Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen.

The fundamental components of protein are nitrogen-containing amino acids , some of which are essential in the sense that humans cannot make them internally. Some of the amino acids are convertible with the expenditure of energy to glucose and can be used for energy production, just as ordinary glucose, in a process known as gluconeogenesis. By breaking down existing protein, the carbon skeleton of the various amino acids can be metabolized to intermediates in cellular respiration; the remaining ammonia is discarded primarily as urea in urine.

Carbohydrates may be classified as monosaccharides , disaccharides , or polysaccharides depending on the number of monomer sugar units they contain. They constitute a large part of foods such as rice , noodles , bread , and other grain -based products, also potatoes , yams, beans, fruits, fruit juices and vegetables. Monosaccharides, disaccharides, and polysaccharides contain one, two, and three or more sugar units, respectively. Polysaccharides are often referred to as complex carbohydrates because they are typically long, multiple branched chains of sugar units.

Traditionally, simple carbohydrates are believed to be absorbed quickly, and therefore to raise blood-glucose levels more rapidly than complex carbohydrates. This, however, is not accurate. 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.

Utilization of food by the body

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 subcategories: Whole grains, fruits especially plums , prunes , 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 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. The link between increased fiber consumption and a decreased risk of colorectal cancer is still uncertain. 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 depending 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 , so 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. 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 partial hydrogenation. There are nine kilocalories in each gram of fat. Fatty acids such as conjugated linoleic acid , catalpic acid, eleostearic acid and punicic acid , in addition to providing energy, represent potent immune modulatory molecules.

Saturated fats typically from animal sources have been a staple in many world cultures for millennia. Saturated and some trans fats are typically solid at room temperature such as butter or lard , while 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 the body can produce them as needed, generally from other fatty acids and always by expending energy to do so.

However, in humans, at least two fatty acids are essential and must be included in the diet.

An appropriate balance of essential fatty acids— omega-3 and omega-6 fatty acids —seems also important for health, although definitive experimental demonstration has been elusive. 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. The omega-6 dihomo-gamma-linolenic acid DGLA serves as a building block for series 1 prostaglandins e. 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 amounts 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. Moreover, the conversion desaturation of DGLA to AA is controlled by the enzyme deltadesaturase , which in turn is controlled by hormones such as insulin up-regulation and glucagon down-regulation. The amount and type of carbohydrates consumed, along with some types of amino acid, can influence processes involving insulin, glucagon, and other hormones; therefore, the ratio of omega-3 versus omega-6 has wide effects on general health, and specific effects on immune function and inflammation , and mitosis i.

Proteins are structural materials in much of the animal body e. They also form the enzymes that control chemical reactions throughout the body. Each protein molecule is composed of amino acids , which are characterized 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 some situations: A complete protein source contains all the essential amino acids; an incomplete protein source lacks one or more of the essential amino acids.

It is possible with protein combinations of two incomplete protein sources e. However, complementary sources of protein do not need to be eaten at the same meal to be used together by the body. Water is excreted from the body in multiple forms; including urine and feces , sweating , and by water vapour in the exhaled breath. Therefore, it is necessary to adequately rehydrate to replace lost fluids. Early recommendations for the quantity of water required for maintenance of good health suggested that 6—8 glasses of water daily is the minimum to maintain proper hydration.

Most of this quantity is contained in prepared foods. For healthful hydration, the current EFSA guidelines recommend total water intakes of 2. These reference values include water from drinking water, other beverages, and from food. The EFSA panel also determined intakes for different populations. Recommended intake volumes in the elderly are the same as for adults as despite lower energy consumption, the water requirement of this group is increased due to a reduction in renal concentrating capacity. Dehydration and over-hydration - too little and too much water, respectively - can have harmful consequences.

Drinking too much water is one of the possible causes of hyponatremia , i. Pure ethanol provides 7 calories per gram. For distilled spirits , a standard serving in the United States is 1. A 5 ounce serving of wine contains to calories. A 12 ounce serving of beer contains 95 to calories. Alcoholic beverages are considered empty calorie foods because other than calories, these contribute no essential nutrients.

The micronutrients are minerals , vitamins , and others. Dietary minerals are inorganic chemical elements required by living organisms, [72] other than the four elements carbon , hydrogen , nitrogen , and oxygen that 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.

Some 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. On the other hand, minerals are often artificially added to the diet as supplements; the most famous is likely iodine in iodized salt which prevents goiter.

Many elements are essential nutrients called dietary minerals. Some have roles as cofactors , while others are electrolytes. Many elements are required in trace amounts, usually because they play a catalytic role in enzymes.

Programme structure:

Vitamins are essential nutrients, [72] necessary in the diet for good health. Vitamin D is an exception, as it can be synthesized in the skin in the presence of UVB radiation , and many animal species can synthesize vitamin C. Vitamin deficiencies may result in disease conditions, including goitre , scurvy , osteoporosis , impaired immune system, disorders of cell metabolism, certain forms of cancer, symptoms of premature aging, and poor psychological health , among many others. Phytochemicals such as polyphenols are compounds produced naturally in plants phyto means "plant" in Greek.

In general, the term identifies compounds that are prevalent in plant foods, but are not proven to be essential for human nutrition, as of There is no conclusive evidence in humans that polyphenols or other non-nutrient compounds from plants confer health benefits, mainly because these compounds have poor bioavailability , i,e. While 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.

Health effects of non-nutrient phytochemicals such as polyphenols were not assessed in this review. Animal intestines contain a large population of gut flora. In humans, the four dominant phyla are Firmicutes , Bacteroidetes , Actinobacteria , and Proteobacteria. 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 B 12 , and defending against some infectious diseases.

There is not yet a scientific consensus as to health benefits accruing from probiotics or prebiotics. Carnivore and herbivore diets are contrasting, with basic nitrogen and carbon proportions vary for their particular foods. Many herbivores rely on bacterial fermentation to create digestible nutrients from indigestible plant cellulose, while obligate carnivores must eat animal meats to obtain certain vitamins or nutrients their bodies cannot otherwise synthesize.

Plant nutrition is the study of the chemical elements that are necessary for plant growth.

Some elements are directly involved in plant metabolism. However, this principle does not account for the so-called beneficial elements, whose presence, while not required, has clear positive effects on plant growth. A nutrient that is able to limit plant growth according to Liebig's law of the minimum is considered an essential plant nutrient if the plant cannot complete its full life cycle without it. There are 16 essential plant soil nutrients, besides the three major elemental nutrients carbon and oxygen that are obtained by photosynthetic plants from carbon dioxide in air, and hydrogen , which is obtained from water.

Plants uptake essential elements from the soil through their roots and from the air consisting of mainly nitrogen and oxygen through their leaves. Green plants obtain their carbohydrate supply from the carbon dioxide in the air by the process of photosynthesis. Carbon and oxygen are absorbed from the air, while other nutrients are absorbed from the soil.

These hydrogen ions displace cations attached to negatively charged soil particles so that the cations are available for uptake by the root. In the leaves, stomata open to take in carbon dioxide and expel oxygen. The carbon dioxide molecules are used as the carbon source in photosynthesis. Although nitrogen is plentiful in the Earth's atmosphere, very few plants can use this directly.

Most plants, therefore, require nitrogen compounds to be present in the soil in which they grow. This is made possible by the fact that largely inert atmospheric nitrogen is changed in a nitrogen fixation process to biologically usable forms in the soil by bacteria. Plant nutrition is a difficult subject to understand completely, partially because of the variation between different plants and even between different species or individuals of a given clone.

Elements present at low levels may cause deficiency symptoms, and toxicity is possible at levels that are too high. Furthermore, deficiency of one element may present as symptoms of toxicity from another element, and vice versa. Canada's Food Guide is an example of a government-run nutrition program.

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Produced by Health Canada , the guide advises food quantities, provides education on balanced nutrition, and promotes physical activity in accordance with government-mandated nutrient needs. Like other nutrition programs around the world, Canada's Food Guide divides nutrition into four main food groups: Dietary and physical activity guidelines from the USDA are presented in the concept of MyPlate , which superseded the food pyramid , which replaced the Four Food Groups.

Department of Health and Human Services provides a sample week-long menu that fulfills the nutritional recommendations of the government. Governmental organisations have been working on nutrition literacy interventions in non-primary health care settings to address the nutrition information problem in the U.

The FNP has developed a series of tools to help families participating in the Food Stamp Program stretch their food dollar and form healthful eating habits including nutrition education. It is designed to assist limited-resource audiences in acquiring the knowledge, skills, attitudes, and changed behavior necessary for nutritionally sound diets, and to contribute to their personal development and the improvement of the total family diet and nutritional well-being.

Launched in , this program promotes lifelong healthful eating patterns and physically active lifestyles for children and their families. It is an interactive educational program designed to help prevent childhood obesity through classroom activities that teach children healthful eating habits and physical exercise.

Nutrition is taught in schools in many countries. In England and Wales , the Personal and Social Education and Food Technology curricula include nutrition, stressing the importance of a balanced diet and teaching how to read nutrition labels on packaging. In many schools, a Nutrition class will fall within the Family and Consumer Science or Health departments.

In some American schools, students are required to take a certain number of FCS or Health related classes. Nutrition is offered at many schools, and, if it is not a class of its own, nutrition is included in other FCS or Health classes such as: In many Nutrition classes, students learn about the food groups, the food pyramid, Daily Recommended Allowances, calories, vitamins, minerals, malnutrition, physical activity, healthful food choices, portion sizes, and how to live a healthy life.

In the US, Registered dietitian nutritionists RDs or RDNs [94] are health professionals qualified to provide safe, evidence-based dietary advice which includes a review of what is eaten, a thorough review of nutritional health, and a personalized nutritional treatment plan. They also provide preventive and therapeutic programs at work places, schools and similar institutions. Certified Clinical Nutritionists or CCNs, are trained health professionals who also offer dietary advice on the role of nutrition in chronic disease, including possible prevention or remediation by addressing nutritional deficiencies before resorting to drugs.

These Board Certified Nutritionists typically specialize in obesity and chronic disease. In order to become board certified, potential CNS candidate must pass an examination, much like Registered Dieticians. This exam covers specific domains within the health sphere including; Clinical Intervention and Human Health.

The study found that health literacy increases with education and people living below the level of poverty have lower health literacy than those above it. Another study examining the health and nutrition literacy status of residents of the lower Mississippi Delta found that 52 percent of participants had a high likelihood of limited literacy skills. For example, only 12 percent of study participants identified the My Pyramid graphic two years after it had been launched by the USDA.

The study also found significant relationships between nutrition literacy and income level and nutrition literacy and educational attainment [98] further delineating priorities for the region. Among these problems are the lack of information about food choices, a lack of understanding of nutritional information and its application to individual circumstances, limited or difficult access to healthful foods, and a range of cultural influences and socioeconomic constraints such as low levels of education and high levels of poverty that decrease opportunities for healthful eating and living.

The links between low health literacy and poor health outcomes has been widely documented [99] and there is evidence that some interventions to improve health literacy have produced successful results in the primary care setting. More must be done to further our understanding of nutrition literacy specific interventions in non-primary care settings [98] in order to achieve better health outcomes.

Malnutrition refers to insufficient, excessive, or imbalanced consumption of nutrients by an organism. In developed countries, the diseases of malnutrition are most often associated with nutritional imbalances or excessive consumption. In developing countries, malnutrition is more likely to be caused by poor access to a range of nutritious foods or inadequate knowledge. The aim was to boost nutrition and livelihoods by producing a product that women could make and sell, and which would be accepted by the local community because of its local heritage.

ULs are set a safe fraction below amounts shown to cause health problems. ULs are part of Dietary Reference Intakes. When too much of one or more nutrients is present in the diet to the exclusion of the proper amount of other nutrients, the diet is said to be unbalanced. High calorie food ingredients such as vegetable oils, sugar and alcohol are referred to as "empty calories" because they displace from the diet foods that also contain protein, vitamins, minerals and fiber.

Health and nutrition appear to have close links with overall educational success. Nutritional supplement treatment may be appropriate for major depression , bipolar disorder , schizophrenia , and obsessive compulsive disorder , the four most common mental disorders in developed countries. Since the Industrial Revolution some two hundred years ago, the food processing industry has invented many technologies that both help keep foods fresh longer and alter the fresh state of food as they appear in nature.

Cooling is the primary technology used to maintain freshness, whereas many more technologies have been invented to allow foods to last longer without becoming spoiled.

These latter technologies include pasteurisation , autoclavation , drying , salting , and separation of various components, all of which appearing to alter the original nutritional contents of food. Pasteurisation and autoclavation heating techniques have no doubt improved the safety of many common foods, preventing epidemics of bacterial infection. But some of the new food processing technologies have downfalls as well.

Modern separation techniques such as milling , centrifugation , and pressing have enabled concentration of particular components of food, yielding flour, oils, juices, and so on, and even separate fatty acids, amino acids, vitamins, and minerals. Inevitably, such large-scale concentration changes the nutritional content of food, saving certain nutrients while removing others.

Heating techniques may also reduce food's content of many heat-labile nutrients such as certain vitamins and phytochemicals, and possibly other yet-to-be-discovered substances. In addition, processed foods often contain potentially harmful substances such as oxidized fats and trans fatty acids. A dramatic example of the effect of food processing on a population's health is the history of epidemics of beri-beri in people subsisting on polished rice.

Removing the outer layer of rice by polishing it removes with it the essential vitamin thiamine , causing beri-beri. Another example is the development of scurvy among infants in the late 19th century in the United States. It turned out that the vast majority of sufferers were being fed milk that had been heat-treated as suggested by Pasteur to control bacterial disease. Pasteurisation was effective against bacteria, but it destroyed the vitamin C.

As mentioned, lifestyle- and obesity-related diseases are becoming increasingly prevalent all around the world. There is little doubt that the increasingly widespread application of some modern food processing technologies has contributed to this development. The food processing industry is a major part of modern economy, and as such it is influential in political decisions e.

In any known profit-driven economy, health considerations are hardly a priority; effective production of cheap foods with a long shelf-life is more the trend. In general, whole, fresh foods have a relatively short shelf-life and are less profitable to produce and sell than are more processed foods. Thus, the consumer is left with the choice between more expensive, but nutritionally superior, whole, fresh foods, and cheap, usually nutritionally inferior, processed foods. Because processed foods are often cheaper, more convenient in both purchasing, storage, and preparation , and more available, the consumption of nutritionally inferior foods has been increasing throughout the world along with many nutrition-related health complications.

From Wikipedia, the free encyclopedia. This article is about Nutrition in general. For Nutrition in humans, see Human nutrition. For Nutrition in animals, see Animal nutrition. For nutrition in plant, see Plant nutrition. This gives the stomach a pH of 1 to 2. This acid kills many bacteria, loosens food, converts pepsinogen into pepsin, and denatures salivary amylase.

When this acid is overproduced it sometimes rises up into the oesophagus. Neutralising the acid with a base such as Rennies can control this condition. As the stomach wall contracts the food is churned and thus digested mechanically. The food becomes a thick milky mixture called chyme. This chyme will leave the stomach and go into the small intestine. To do so, it goes through the pyloric sphincter. The cells of the stomach are replaced very rapidly. A million are produced per minute.

In this way, damaged stomach cells are constantly being replaced. If the defence mechanisms to stop self-digestion of the stomach fail, then peptic ulcers of the stomach form. These cause bleeding and may dissolve the stomach lining all the way through the stomach wall. It is now called a perforated ulcer. This is very dangerous as bacteria may travel through the ulcer and into the body cavity.

In some cases it can cause death. The small intestine is where the food is absorbed into the blood to be taken to the body cells. The small intestine is about 6 metres long.

It is made up of 3 parts. The duodenum, jejunum, and ileum. The duodenum- The main function of the duodenum is to finish the digestive process. The cells lining the duodenum produce digestive enzymes. Also, products from the pancreas and the liver enter the duodenum to do their work. The lining of the small intestine consists of many folds called villi. Each villus has about microvilli. These foldings and microvilli increase the surface area of the small intestine for increased digestion or absorption. Intestinal glands are located between the villi.

These glands produce numerous enzymes, which are collectively called intestinal juices. These enzymes enter the and do their digestive work at the duodenum. They enter the duodenum through the pancreatic duct. Bile is a yellow-green liquid that is produced in the liver and stored in the gall bladder. Bile enters the duodenum through the bile duct. Bile has the following functions:. Emulsifies lipids- It breaks down large fat and oil molecules into tiny droplets. In this way, the surface area of the lipids is increased and enzyme action is more efficient.

By the time the food enters this part of the small intestine it is fully digested. The job of the jejunum and ileum is to absorb the food. The lining of these sections of the small intestine contain many villi. The walls of the villi are only 1 cell thick. There is a rich supply of blood located inside each villus.

The capillaries of each villus absorb nutrients from the food and, in this way, the food gets into the blood supply. Foods such as glucose, amino acids, vitamins, and minerals are absorbed into the blood here.

The food is then taken to the hepatic portal vein which takes it to the liver. Here the food is stored and released when needed by the body. Amino acids are not stored but, those not used by the body, are broken down by the liver and form urea. This process is called deamination. Wastes created at the liver go from the liver to the hepatic vein and then to the kidneys.

Here they are excreted. Fats fatty acids and glycerols are absorbed into the villis lacteals. The lacteals have lymph fluid in them. The large intestine is the last part of the alimentary canal. Here is where the final phase of the nutrition process occurs. The large intestine is larger in diameter than the small intestine. That is why it is called large. It has a diameter of about 6 cm.

Human Nutrition

As compared to the small intestine s diameter of about 3 cm. It s length is about 1. Food stays in the large intestine for varying lengths of time from 10 hours to as long as a few days. The caecum is right below the junction of the large and small intestine. The appendix is at the end of the caecum. The function of them in humans is not known. In herbivores they serve as an area where bacteria exist and aid in the digestion of cellulose. The organs are said to be vestigal organs.

Positively Impacting Health

They have lost their prior use. If bacteria do grow in the appendix or there is a faecal blockage pain is produced in the appendix. If not treated the appendix may burst and cause infection the the abdominal lining. This condition is called peritonitis. Usually the appendix is removed to avoid this serious condition. The colon absorbs water from the remaining food that has past through the alimentary canal. The waste then becomes a semi-solid called faeces. Faeces are stored in the rectum and then egested through the anus. Bacteria that live in the colon feed on the waste and produce some B vitamins as well as Vitamin K.

These vitamins are absorbed into the blood stream at the colon. There are other bacteria in the digestive system that help break down food, especially cellulose. This is a symbiotic relationship. The bacteria obtain nourishment and we obtain vitamins and digested food. From the food we get energy for our bodies to function and protein for growth. The energy content is measured in joules J or kilojoules kJ. The old units of energy were calories or kilocalories. Fats contain about twice as many joules as carbohydrates. There are four food groups. The foods in each food group contain similar nutrients.

See the table below for the food groups and the suggested servings per day for each food group.

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