What Is Nutrition? Why Is Nutrition Important?

Editor's Choice
Main Category: Nutrition / Diet
Also Included In: Biology / Biochemistry
Article Date: 16 Aug 2009 - 0:00 PDT

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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.

What is the difference between a dietician and a nutritionist?

A dietician studied dietetics, while a nutritionist studied nutrition. The two terms are often interchangeable, however they are not 100% identical.

• Dietetics: the interpretation and communication of the science of nutrition so that people can make informed and practical choices about food and lifestyle, in both health and disease. Part of a dietician's course includes both hospital and community settings. The majority of dieticians work in health care, education and research, while a much smaller proportion also work in the food industry. A dietician must have a recognized degree (B.Sc. or M.Sc), or postgraduate degree in nutrition and dietetics to work as a dietician.


• Nutrition: the study of nutrients in food, how the body uses nutrients, and the relationship between diet, health and disease. Major food manufacturers employ nutritionists and food scientists. Nutritionists may also work in journalism, education and research. Many nutritionists work in the field of food science and technology.

There is a lot of overlap between what nutritionists and dieticians do and studied. Some nutritionists work in health care, some dieticians work in the food industry, but a higher percentage of nutritionists work in the food industry and food science and technology, and a higher percentage of dieticians work in health care.

One could very loosely generalize and say that a nutritionist focuses firstly on a food, and then looks at its effects on people, while a dietician looks at the human, and then how that human's health is influenced by food.

If I discovered a new fruit and wanted to find out what it consisted of I would go to a nutritionist. If I found out I had a long-term disease and wanted to know whether I needed to adjust my food intake because of the disease, I would go to a dietician. Please bear in mind that this very loose comparison is both subjective and possibly too geographically bound on my part (British, National Health Service), and is simply aimed at exaggerating the differences so that lay people may see some gap between the two - differences and disagreements in my interpretation will exist in different countries, within regions of a countries, and also from college to college - and many in those areas will disagree with each other.

From what I can glean from hundreds of studies and texts that I read as an editor of a medical journal, in the USA, Australia, and to a lesser extent in the UK and the Republic of Ireland, people who call themselves dieticians are more likely to have full university bachelor's or postgraduate qualifications, while nutritionists mostly do as well, but a higher proportion may not.

In the US, dietitians are registered or licensed with the Commission for Dietetic Registration and the American Dietetic Association, and are only able to use the title dietitian as described by the business and professions codes of each respective state, when they have met specific educational and work experience requirements and passed a national registration or licensure examination, respectively.

Everyone in medicine is involved in nutrition

If you ask any health care professional, be it a doctor, nurse, psychologist, or dentist to identify a part of medicine that is not at all related to nutrition, there will be a long silence as they scratch their heads.

Nutrition is present in all processes of life. Right from the very moment the sperm fertilizes an egg, through fetal development in the uterus, to the birth, human growth, maturity, old age, and eventual death. Even after death the human body serves as nutrition for other organisms. Anything that involves life and chemical or biochemical movement has nutrition at its core.

Anything that lives is dependent on energy, which results from the combustion of food.

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. For more details go to What is fiber? What is dietary fiber?


• 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.

A brief history of nutrition

• The Bible, Book of Daniel - Daniel was captured by the King of Babylon and had to serve in the King's court. Daniel objected to being fed fine foods and wine, saying he preferred vegetables, pulses and water. The chief steward reluctantly agreed to a trial, comparing Daniel's dietary preference to those of the court of the King of Babylon. For ten days Daniel and his men had their vegetarian diet, while the King's men had theirs. The trial revealed that Daniel and his men were healthier and fitter, so they were allowed to carry on with their diet.


• Hippocrates (Greece, ca460BC - ca370BC), one nutrient theory - according to Hippocrates everybody is the same, no matter what they have been eating, or where they have lived. He concluded that every food must contain one nutrient which makes us the way we are. This one-nutrient myth continued for thousands of years. Hippocrates is also famous for having said "Let thy food be thy medicine and thy medicine be thy food."


• Antoine Lavoisier (France, 1743-1794) - became known as the father of chemistry and also the father of nutrition. He became famous for the statement "Life is a chemical process". He also designed the "calorimeter", a device which measured heat produced by the body from work and consumption from different amounts and types of foods. At the age of 24 he became a member of the French Academy of Science. In 1794, during the French Revolution, he was beheaded.


• Christiaan Eijkman (Holland, 1858-1930) - a famous physician and pathologist (doctor who identifies diseases by studying cells and tissues under a microscope). He noticed that some of the people in Java developed Beriberi, a disease which leads to heart problems and paralysis. When he fed chickens a diet consisting mainly of white rice they also developed Beriberi type symptoms, but the chickens fed unprocessed brown rice did not. White rice has the outer bran removed, while brown rice does not. When he fed brown rice to patients with Beriberi they were cured. Many years later it was found that the outer husks (outer bran) in rice contain thiamine, or vitamin B₁. Together with Sir Frederick Hopkins, he received the Nobel Prize for Physiology/Medicine.


• Dr. James Lind (Scotland, 1716-1794) - a pioneer on hygiene in the Scottish and Royal (British) navies. He stressed the importance of good ventilation, cleanliness of sailor's bodies, clean bedding, below deck fumigation, fresh water by distilling sea water, and the consumption of citrus fruits to prevent and cure scurvy. He is well respected today for his work in improving practices in preventive medicine and improved nutrition. He published his Treatise on Scurvy. Many decades later British sailors were known as Limeys because they regularly consumed lime juice and enjoyed better health and vigor than sailors in most other navies.


• Dr. William Beaumont (USA, 1785-1853) - a surgeon in the US Army. He became known as the Father of gastric physiology for his research on human digestion. Beaumont met Alexio St. Martin, a French trapper who was shot in the stomach. Beaumont treated him but was unable to close the hole in his stomach, which healed with an opening to the outside (a fistula). St. Martin allowed Beaumont to make observations periodically, even allowing him to fiddle around with his innards, which must have been painful. This allowed Beaumont to conduct several experiments and make some important discoveries and conclusions, including:
  
  
  • The stomach is not a grinder.
  • There is no internal "spirit" selecting good purpose foods one way and discarding bad purpose foods to waste.
  • Digestion occurs because of digestive juices which are secreted from the stomach.
  • Foods are not digested separately and sequentially, but rather all the time and at different rates.
  • Stomach rumblings are caused by stomach contractions, and nothing else.
  • Fat is digested slowly.


• Dr. Stephen Babcock (USA, 1843-1931) - an agricultural chemist. He is known for his Babcock test which determines dairy butterfat in milk and cheese processing. He is also known for the single-grain experiment that eventually led to the development of nutrition as a science.
  
  Babcock had the idea of feeding dairy cattle with just one food source, either all corn plant or all wheat plant. He placed two heifers on either diet. However, when one of his animals died they were all taken away and he was not allowed to continue researching.
  
  Eventually, Babcock's associates, Hart, Humphrey, McCollum, and Steenbock conducted the experiments again. Four five-month-old heifers were each fed either exclusively feed from corn plant, wheat plant, oat plant, or all three mixed together. They all put on weight at approximately the same rate during the first 12 months. However, the corn-fed cows went on to have normal calves, while the wheat-fed cows gave birth to either dead calves or calves that died soon after birth. They also noted that the corn-fed cows produced three times as much milk as the wheat-fed ones. They concluded that:
  
  
  either
  
  • the wheat contained something that was bad for the cows
  or
  
  • the corn had an essential nutrient that wheat did not have
  
  A succession of discoveries eventually found that something in the fat soluble portion of the corn affected reproduction. The scientists called this factor A - What we know today as Vitamin A.


• Kazimierz Funk (Poland,1884- 1967) - a biochemist. Funk mistakenly thought these new things being discovered, such as factor A contained animes. As these animes were vital, he coined the term vitamins (vital animes).

As research evolved and further active properties were found, the water soluble ones were labeled B. It became obvious that more than one thing was involved in the water soluble substance, leading to the labels B1, B2, B3, etc. Some turned out not to be vitamins, while others were found to be the same as others - this explains why B vitamin numbers suddenly jump from 9 to 12, or 7 to 9. Vitamin B₁₂ was discovered in 1948 by Karl A. Folkers (USA) and Alexander R. Todd (UK) and reported in 1949. They isolated the active ingredient, a cobalamin. It could also be injected straight into muscle as a treatment for pernicious (potentially fatal) anemia.

Vitamin C was clarified thanks to research carried out with guinea pigs. Very few animals, including humans, guinea pigs, primates, some bats, some birds, and some reptiles require vitamin C from food - all other animals are able to synthesize it internally (produce it themselves).

The era of discovering disease-preventing essential nutrients ended in 1948/49 with the discovery of Vitamin B₁₂. Some other substances have since been discovered outside this "era" of great discoveries.

Some other famous people in the history of nutrition:

• 1925 - Edwin B. Hart discovered that trace amounts of copper are essential for iron absorption.


• 1927 - Adolf Otto Reinhold Windaus synthesized Vitamin D, for which he won the Nobel Prize in Chemistry.


• 1928 - Albert Szent-Györgyi isolated ascorbic acid (Vitamin C). In 1932 he proved that it was Vitamin C by preventing scurvy. In 1937 he synthesized Vitamin C and won the Nobel Prize.


• 1930s - William Cumming Rose identified essential amino acids which the body cannot synthesize, but which are necessary protein components.


• 1935 - Eric John Underwood and Hedley Marston discovered the necessity of cobalt. They were not working together - the discoveries were made independently.


• 1936 - Eugene Floyd Dubois demonstrated that school and work performance are linked to caloric intake.


• 1938 - Erhard Ferhnholz discovered the structure of Vitamin E, which was later synthesized by Paul Karrer.


• 1940 - Elsie Widdowson drew up the nutritional principles for rationing which took place in the United Kingdom during and after World War II. Widdowson also oversaw the government mandated addition of vitamins to food during World War II and some post-war years. Widdowson and Robert McCance coauthored The Chemical Composition of Foods in 1940, which became the basis for modern nutritional thinking.


• 1941 - The National Research Council (USA) set up the first RDAs (Recommended Dietary Allowances).


• 1968 - Linus Pauling coined the term orthomolecular nutrition. He proposed that by giving the body the right molecules in the right concentration - optimum nutrition - these nutrients would be better utilized and provide superior health and contribute towards longer lives. Pauling's work was the basis for future research which eventually led to large intravenous doses of Vitamin C for improving survival times and quality of life of some terminal cancer patients. Pauling was awarded the Nobel Prize in Chemistry.


• 1992 - the Department of Agriculture (USA) set up the Food Guide Pyramid, which was to be subsequently criticized by nutritionists throughout the world for different reasons.


• 2002 - a link between violent behavior and nutrition was revealed in a Natural Justice study (USA).


• 2005 - researchers found that the adenovirus is a cause of obesity, as well as bad nutrition.

Nutrition in medical education

Historically, experts in medical education - people who decide what medical students should learn - have all agreed that some aspects of nutrition should be included in courses. However, the greatest obstacle for a very long time was agreeing about what to teach. In 1989 the American Society for Clinical Nutrition Committee on Medical/Dental School and Residency Nutrition Education published a list of 26 high-priority topics that should form part of the medical curriculum. Those given the highest priority were:

• Obesity
• Diet
• Hypelipidemias and atherosclerosis
• Diet and diabetes
• Pregnancy and lactation

Roland L Weinsier et al
"Priorities for nutrition content in a medical school curriculum: a national consensus of medical educators13"
(Am J Clin Nutr 1989; Vol 50, 707-712).

In 1996 the Nutrition and Preventative Medicine Task Force of the American Medical Student Association formed the Nutrition Curriculum Project, and developed a list of 92 topics deemed essential for developing physicians' competency in nutrition.

"Essentials of nutrition education in medical schools: a national consensus. American Medical Student Association's Nutrition Curriculum Project"
(Academic Medicine. 71(9):969-71, September 1996).

Written by Christian Nordqvist


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