# Human Physiology/Nutrition

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## The Community and Nutrition Programs

Harvard's Food Pyramid

Connections between nutrition and health have probably been understood, at least to some degree, among all people of all places and times. For example, around 400 BC Hippocrates said, "Let food be your medicine and medicine be your food." Understanding the physiological needs of our cells helps us understand why food has such an impact on overall health. In this chapter we introduce nutrition by examining how cells use different nutrients and then discuss disease conditions that are tied to nutritional problems.

## Nutrition and Health in the Community

The nutritional status of people in our communities is a concern not only for quality of life, but also for economics (treating illness costs far more than preventing it). Various public health agencies are striving to prevent nutritional deficiencies and improve overall health. In the U.S., the government supplies a variety of resources such as state assistance, WIC (Women Infant and Child), and so forth. In addition, there have been many government agencies and voluntary health and scientific associations, such as the American Heart Association, that focus on life style and dietary factors that prevent chronic and life-threatening diseases. The U.S. Department of Agriculture (USDA) and the U.S. Department of Health and Human Services (USDHHS) developed dietary guidelines in 1977 that were compiled and displayed as the food guide pyramid. The food guide pyramid was revised as "My Pyramid," but this new chart is confusing to most people. Harvard School of Public Health developed an alternative healthy eating pyramid (shown at left) based on long-term nutritional studies. This pyramid differs from the old USDA pyramid in several key aspects: for example, exercise is at the bottom to remind us of its important role in our health. Also, not all carbohydrates are at the bottom (white bread, white rice, and potatoes are now at the top with sugars), and not all oils are at the top (plant oils are at the bottom). Other resource, such as the Recommended Daily Allowance (RDA) have helped people become more aware of nutritional needs, yet obesity and chronic health problems continue to rise.

## Nutritional Requirements

Our bodies have both caloric and nutritional needs. Living tissue is kept alive by the expenditure of energy in ATP molecules, which energy came from the break down of food molecules. Caloric need refers to the energy needed each day to carry out the varied chemical reactions in each cell. When looking at a nutritional label, we can easily see how many Calories are in a serving. These Calories (big "C") are actually kilocalories (1000 calories). Technically, a calorie (little "c") is the amount of energy needed to raise the temperature of 1 mL of water by 1 °C. How many Calories a person needs daily varies greatly by age, sex, height, and physical activity levels. If the amount of energy taken in exceeds the amount of energy used, then the excess energy is stored as adipose tissue (fat), regardless of the source of the energy.

In addition to daily energy needs, there are nutritional needs to prevent the body from losing its own fats, carbohydrates, and proteins. Such molecules are continuously broken down, and must be replaced regularly. Essential amino acids and essential fatty acids are particularly important building blocks in replacing these molecules. Vitamins and minerals are not used as energy, but are essential in tissue and enzyme structure or reactions.

## Carbohydrates

Macronutrient
An energy-yielding nutrient. Macronutrients are those nutrients that together provide the vast majority of metabolic energy to an organism. The three main macronutrients are carbohydrates, proteins, and fat.
Micronutrients
Microminerals or trace elements, are dietary minerals needed by the human body in very small quantities (generally less than 100mg/day) as opposed to macrominerals which are required in larger quantities.

Functions

Glucose it is the most easily used by the body. It is a simple carbohydrate that circulates in the blood and is the main source of energy for the muscles, central nervous system, and brain (the brain can also use ketone bodies).

Carbohydrates are made of organic compounds carbon, hydrogen, and oxygen.

There are three sizes of carbohydrate and they are distinguished by a classification of two that is, simple carbohydrates (mono saccharides and disaccharides) and complex carbohydrates (polysaccharides). Polysaccharides are the most abundant carbohydrate in the body along with glycogen.

The break down of polysaccharides goes as follows: Polysaccharides are digested into monosaccharides including glucose which goes into the intestinal epithelium and into the bloodstream. The molecules of glucose are taken by glucose transporters and delivered into the cells of the body. While glucose is in the cells it can be oxidized for energy or provide substrates to other metabolic reactions or of course into glycogen for storage.

A. Monosaccharides = Single carbohydrate unit such as, Glucose, Fructose, and Galactose.
B. Disaccharides = Two single carbohydrates bound together such as, Sucrose, Maltose, and Lactose.
C. Polysaccharides = Have many units of monosaccharides joined together such as, Starch and Fiber.

Fiber

Fiber is carbohydrates that cannot be digested. It is in all eatable plants such as fruits vegetables, grains and Legumes. There are many ways of categorizing fiber types. First, from the foods they come from such as grains, which is called cereal fiber. Second, if they are soluble fiber or insoluble fiber. Soluble fiber partially dissolves in water and insoluble fiber does not.

Adults need about 21-38 grams of fiber a day. Children ages 1 and up need 19 grams a day. On average Americans eat only 15 grams a day.

Fiber helps reduce the chances of having the following conditions: colon cancer, heart disease, type 2 diabetes, diverticular disease, and constipation.

Glycemic Index

Glycemic Index is a new way of classifying carbohydrates. It measures how fast and how far blood sugar will rise after consuming carbohydrates. Foods that are considered to have a high glycemic index are converted almost immediately to blood sugar which causes it to rise rapidly. Foods that are considered to have a low glycemic index are digested slower causing a slower rise in blood sugar. Examples of high glycemic index foods are potatoes, white rice, white flour, anything refined, anything with a lot of sugar which includes high fructose corn syrup. Examples of low glycemic index foods are whole grains (brown rice, 100% whole wheat bread, whole grain pasta, high fiber cereals), high fiber fruits and vegetables, and many legumes. According to the Harvard School of Public Health, "The most comprehensive list of the glycemic index of foods was published in the July, 2002, issue of the American Journal of Clinical Nutrition. A searchable database maintained by the University of Sydney is available online."

## Proteins

Functions

Protein forms hormones, enzymes, and antibodies. It is part of fluid and electrolyte regulation, the buffering effect for pH, and transporter of nutrients. A good example of a protein is the oxygen carrying hemoglobin found in red blood cells.

Proteins are made of carbon, hydrogen, oxygen, and nitrogen, an inorganic molecule, the thing that clearly distinguishes them from the other macronutrients.

A. Amino acids are the building blocks of proteins.

B. Polypeptide are a group of amino acids bonded together 10-100 or more.

The body requires amino acids to produce new body protein (protein retention) and to replace damaged proteins (maintenance) that are lost in the urine.

Proteins are relatively large molecules made of amino acids joined together in chains by peptide bonds. Amino acids are the basic structural building units of proteins. They form short polymer chains called peptides or longer poly-peptides which in turn form structures called proteins. The process of protein synthesis is controlled by an mRNA template. In this process tRNA transfers amino acids to the mRNA to form protein chains.

There are twenty standard amino acids used by cells in making proteins. Vertebrates, including humans, are able to synthesize 11 of these amino acids from other molecules. The remaining nine amino acids cannot be synthesized by our cells, and are termed "'essential amino acids'". These essential amino acids must be obtained from foods.

The 9 Essential Amino Acids have the following names: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine

You can remember these with this saying “Hey It's Like Lovely Material; Please Touch The Velvet”.

The 11 Non-essential Amino Acids are as follows:

Alanine, Arginine, Aspartic acid, Cysteine, Cystine, Glutamic acid, Glutamine, Glycine, Proline, Serine, Tyrosine

How about this memory device, "Almost Always Aunt Cindy Can Get Great Gum Popping Sounds Together" (This section needs to be corrected. Cystine is not one of the 20 common amino acids. It should be replaced by asparagine which is missing from the list. Also histidine is not essential for adults while cysteine, tyrosine, histidine, and arginine are required for infants and growing children. Some amino acids are also essential for specific subpopulations, e.g., tyrosine for individuals with PKU.)

### The 20 Amino Acids and What They Do!

Amino Acid Abbrev. Remarks
Alanine A Ala Very abundant, very versatile. More stiff than glycine, but small enough to pose only small steric limits for the protein conformation. It behaves fairly neutrally, can be located in both hydrophilic regions on the protein outside and the hydrophobic areas inside.
Cysteine C Cys The sulfur atom binds readily to heavy metal ions. Under oxidizing conditions, two cysteines can join together in a disulfide bond to form the amino acid cystine. When cystines are part of a protein, insulin for example, this stabilizes tertiary structure and makes the protein more resistant to denaturation; disulphide bridges are therefore common in proteins that have to function in harsh environments including digestive enzymes (e.g., pepsin and chymotrypsin) and structural proteins (e.g., keratin). Disulphides are also found in peptides too small to hold a stable shape on their own (e.g., insulin).
Aspartic acid D Asp Behaves similarly to glutamic acid. Carries a hydrophilic acidic group with strong negative charge. Usually is located on the outer surface of the protein, making it water-soluble. Binds to positively-charged molecules and ions, often used in enzymes to fix the metal ion. When located inside of the protein, aspartate and glutamate are usually paired with arginine and lysine.
Glutamate E Glu Behaves similar to aspartic acid. Has longer, slightly more flexible side chain. Also serves as an excitatory neurotransmitter in the CNS.
Phenylalanine F Phe Essential for humans. Phenylalanine, tyrosine, and tryptophan contain large rigid aromatic group on the side chain. These are the biggest amino acids. Like isoleucine, leucine and valine, these are hydrophobic and tend to orient towards the interior of the folded protein molecule.
Glycine G Gly Because of the two hydrogen atoms at the α carbon, glycine is not optically active. It is the smallest amino acid, rotates easily, adds flexibility to the protein chain. It is able to fit into the tightest spaces, e.g., the triple helix of collagen. As too much flexibility is usually not desired, as a structural component it is less common than alanine.
Histidine H His In even slightly acidic conditions protonation of the nitrogen occurs, changing the properties of histidine and the polypeptide as a whole. It is used by many proteins as a regulatory mechanism, changing the conformation and behavior of the polypeptide in acidic regions such as the late endosome or lysosome, enforcing conformation change in enzymes. However only a few histidines are needed for this, so it is comparatively scarce.
Isoleucine I Ile Essential for humans. Isoleucine, leucine and valine have large aliphatic hydrophobic side chains. Their molecules are rigid, and their mutual hydrophobic interactions are important for the correct folding of proteins, as these chains tend to be located inside of the protein molecule.
Lysine K Lys Essential for humans. Behaves similarly to arginine. Contains a long flexible side-chain with a positively-charged end. The flexibility of the chain makes lysine and arginine suitable for binding to molecules with many negative charges on their surfaces. E.g., DNA-binding proteins have their active regions rich with arginine and lysine. The strong charge makes these two amino acids prone to be located on the outer hydrophilic surfaces of the proteins; when they are found inside, they are usually paired with a corresponding negatively-charged amino acid, e.g., aspartate or glutamate.
Leucine L Leu Essential for humans. Behaves similar to isoleucine and valine. See isoleucine.
Methionine M Met Essential for humans. Always the first amino acid to be incorporated into a protein; sometimes removed after translation. Like cysteine, contains sulfur, but with a methyl group instead of hydrogen. This methyl group can be activated, and is used in many reactions where a new carbon atom is being added to another molecule.
Asparagine N Asn Similar to aspartic acid. Asn contains an amide group where Asp has a carboxyl.
Proline P Pro Contains an unusual ring to the N-end amine group, which forces the CO-NH amide sequence into a fixed conformation. Can disrupt protein folding structures like α helix or β sheet, forcing the desired kink in the protein chain. Common in collagen, where it often undergoes a post-translational modification to hydroxyproline. Uncommon elsewhere.
Glutamine Q Gln Similar to glutamic acid. Gln contains an amide group where Glu has a carboxyl. Used in proteins and as a storage for ammonia.
Arginine R Arg Functionally similar to lysine.
Serine S Ser Serine and threonine have a short group ended with a hydroxyl group. Its hydrogen is easy to remove, so serine and threonine often act as hydrogen donors in enzymes. Both are very hydrophilic, therefore the outer regions of soluble proteins tend to be rich with them.
Threonine T Thr Essential for humans. Behaves similarly to serine.
Valine V Val Essential for humans. Behaves similarly to isoleucine and leucine. See isoleucine.
Tryptophan W Trp Essential for humans. Behaves similarly to phenylalanine and tyrosine (see phenylalanine). Precursor of serotonin.
Tyrosine Y Tyr Behaves similarly to phenylalanine and tryptophan (see phenylalanine). Precursor of melanin, epinephrine, and thyroid hormones.

Dietary proteins fall into two categories: complete proteins and incomplete proteins. Complete proteins include ample amounts of all essential amino acids. Examples of foods that will include these great complete proteins are meat, fish, poultry, cheese, eggs, and milk. Incomplete proteins contain some but not all of the essential amino acids required by the human body. Examples of incomplete proteins include legumes, rice, and leafy green vegetables. Someone who chooses a vegan lifestyle must be careful to combine various plant proteins to obtain all the essential amino acids on a daily basis, but it can be accomplished.

Ingested proteins are broken down into amino acids during digestion. They are then absorbed by the villi of the small intestine and enter the blood stream. Our cells use these amino acids to assemble new proteins that are used as enzymes, cell receptors, hormones, and structural features. Each protein has its own unique amino acid sequence that is specified by the nucleotide sequence of the gene encoding that protein (see Genetics and Inheritance). If we are deficient in even a single amino acid, then our cells cannot make the proteins they require.

## Lipids

Macronutrient
Provides 9 Kcalories per gram; it is an energy-yielding nutrient.

Functions are stored energy (adipose tissue), organ protection, temperature regulator, insulation such as myelin that covers nerve cells, lipid membrane around cells, and emulsifiers to keep fats dispersed in body fluids.

Lipids are made of organic molecules carbon, hydrogen, and oxygen. Fats consist of glycerol fatty acids joined by an ester bond.

• A. Triglycerides - composed of three fatty acids and one glycerol molecule.
• B. Saturated fatty acid - fatty acid with carbon chains fully saturated with hydrogen.
• C. Monounsaturated fatty acid - fatty acid that has a carbon chain with one unsaturated double bond.
• D. Polyunsaturated fatty acid - fatty acid that has two or more double bonds on the carbon chain.

Essential fatty acids part of the polyunsaturated fatty acids

• E. Linoleic acid an essential polyunsaturated fatty acid, its first double bond is at the 6th carbon and this is why it can be called Omega 6.
• F. Linolenic acid an essential polyunsaturated fatty acid, its first double bond is at the 3rd carbon and this is why it can be called Omega 3, and is the main member of the omega-3 family.
• G. Eicosapentaenoic acid (EPA) , may be derived inefficiently from linolenic acid and is the main fatty acid found in fish, also called omega 3.
• H. Docosahexaenoic acid (DHA), is an omega 3 fatty acid, is synthesized in body from alph-linolenic acid, and is present in fish. DHA is present in retina and brain.
Nonessential
• I. Sterols serve a vital function in the body, are produced by the body, and are not essential nutrients. This structure of a lipid is cholesterol which is a waxy substance that doesn't look like a triglyceride. It doesn't have a glycerol backbone or fatty acids, but because it is impermeable in water, it is a lipid.
• J. CIS- Trans Fatty acids hydrogenation makes monounsaturated and polyunsaturated fatty acids go from a state of their original form that is cis to a trans form. Addition of hydrogen ions will cause vegetable oil to harden. Additionally, they may stimulate cholesterol synthesis, and are potentially carcinogenic.

Absorption process of triglycerides. This is the fat that your body deals with most of the time. They are absorbed with the transport of chylomicrons into the lymphatic system which in turn will pour into the blood stream at the thoracic duct. Once it enters the blood stream, the chylomicrons take the triglycerides into the cells. The triglycerides that are on the outer part of the chylomicrons are broken down by lipoprotein lipase. Lipoprotein lipase can be found on the walls of capillaries. It is this enzyme that will break it into fatty acids and monoglycerides. The fatty acids are taken by the body's cells while the monoglycerides are taken to the liver to be processed. Medium chain triglycerides (MCTs) bypass chylomicron lipoprotein function allowing the body to quickly utilize them for energy. Due to their shorter chain length, MCTs possess 8.3kcal as opposed to the 9kcal content of long chain triglycerides. MCT consumption due to the immediate utilization by the body also results in the rapid formation of ketones and less ability to be stored as adipose tissue.

• 1. Lipids are structural components found in every cell of the human body. That is, they form the lipid bilayer found in individual cells. They also serve as the myelin sheath found in neurons.
• 2. Lipids provide us with energy. Most of that energy is in the form of triacylglycerols.
• 3. Both lipids and lipid derivatives serve as vitamins and hormones.
• 4. Lipophilic bile acids aid in lipid solubility.

Recommendations for Fat Intake: Although there are different types of fat the effect on health and disease, the basic message is simple: leave out the bad fats and replace them with good fats. Try to limit saturated fats in your diet, and try to eliminate trans fats from partially hydrogenated oils.Replace saturated and trans fats with polyunsaturated and monounsaturated fats. As of January 1, 2006, trans fat must be listed on food labels. More and more "trans-fat" free products are becoming available. Keep in mind, though, that according to the FDA, a product claiming to have zero trans fat can actually contain up to a half gram. You may still want to scan the ingredient list for "partially hydrogenated vegetable oil" and "vegetable shortening," and look for an alternative product without those words.

## Vitamins and Minerals

Fruits and vegetables are often a good source of vitamins.

We all need micronutrients in small quantities to sustain health. Micronutrients include dietary minerals and vitamins. While all minerals and vitamins can be obtained through food, many people do not consume enough to meet their micronutrient needs and instead may take a supplement.

Microminerals or trace elements include at least iron, cobalt, chromium, copper, iodine, manganese, selenium, zinc, and molybdenum. They are dietary minerals needed by the human body in very small quantities (generally less than 100mg/day) as opposed to macrominerals which are required in larger quantities. (Note that the use of the term "mineral" here is distinct from the usage in the geological sciences.)

### Vitamins

Vitamins are organic compounds that are essential for our body to function properly. Most vitamins are obtained from what you consume, because the body is unable to manufacture most of the essential vitamins that you need to survive. Here are types of vitamins and their roles:

Vitamin Food Sources Functions Problems When Deficient Problems With Taking Too Much
A (retinol) Ingested in a precursor form. Found in animal sources such as milk and eggs. Also found in carrots and spinach (contain pro vitamin A carotenoids). Vitamin A is a fat-soluble vitamin. It helps cells differentiate, also lowering your risk of getting cancer. Vitamin A helps to keep vision healthy. It is required during pregnancy. Vitamin A also influences the function and development of sperm, ovaries and placenta and is a vital component of the reproductive process. Night blindness, impaired growth of bones and teeth Headache, dizziness, nausea, hair loss, abnormal development of fetus
B1 (thiamine) Found in wheat germ, whole wheat, peas, beans, enriched flour, fish, peanuts and meats. Vitamin B1 is a water-soluble vitamin that the body requires to break down carbohydrates, fat and protein. The body needs vitamin b in order to make adenine triphosphate (ATP). Vitamin B1 is also essential for the proper functioning of nerve cells. Beriberi, muscular weakness, enlarged heart Can interfere with the absorption of other vitamins
B2 (riboflavin) Found in milk cheese, leafy green vegetables, liver, soybeans yeast and almonds. Exposure to light destroys riboflavin. Vitamin B2 is a water-soluble vitamin that helps the body process amino acids and fats. Activated vitamin B6 and folic acid helps convert carbohydrates to adenosine triphosphate (ATP). Sometimes vitamin B2 can act as an antioxidant. Dermatitis, blurred vision, growth failure Unknown
B3 (niacin) Found in beets, brewer's yeast, beef liver, beef kidney, pork, turkey, chicken, veal, fish, salmon, swordfish, tuna, sunflower seeds, and peanuts. Vitamin B3 is required for cell respiration and helps release the energy in carbohydrates, fats, and proteins. It helps with proper circulation and healthy skin, functioning of the nervous system, and normal secretion of bile and stomach fluids. It is used in the synthesis of sex hormones, treating schizophrenia and other mental illnesses, and as a memory-enhancer. Pellagra, diarrhea, mental disorders High blood sugar and uric acid, vasodilation
C (ascorbic acid) Found in citrus fruits such as oranges, grapefruit and lemon. Vitamin C is an essential water-soluble vitamin. It is needed to make collagen. Vitamin C also aids in the formation of liver bile which helps to detoxify alcohol and other substances. Evidence indicates that vitamin C levels in the eye decrease with age and this may be a cause of cataracts. Vitamin C has been reported to reduce activity of the enzyme, aldose reductase, which helps protect people with diabetes. It may also protect the body against accumulation or retention of the toxic mineral, lead. Scurvy, delayed wound healing, infections Gout, kidney stones, diarrhea, decreased copper
D Produced by the human body during exposure to the ultraviolet rays of the sun. Vitamin D is a fat-soluble vitamin that helps maintain blood levels of calcium. Vitamin D is necessary for healthy bones and teeth. Vitamin D plays a role in immunity and blood cell formation and also helps cells differentiate this lowers your chance of getting cancer. Lack of Vitamin D results in rickets for children and osteomalacia for adults. Calcification of soft tissue, diarrhea, possible renal damage
E Found in vegetable oils, nuts, and green leafy vegetables. Fortified cereals are also an important source of vitamin E in the United States. Vitamin E is an antioxidant that protects cell membranes and other fat-soluble parts of the body, such as LDL cholesterol (the “bad” cholesterol), from damage. Unknown Diarrhea, nausea, headaches, fatigue, muscle weakness
K Found in kale, collard greens, spinach, mustard greens, turnip greens and Brussels sprouts. Also found vegetable oils such as soybean, canola, cottonseed, and olive. Additionally, the normal flora of the large intestine produce vitamin K, which our body is able to absorb and use Vitamin K by helping transport Ca, vitamin K is necessary for proper bone growth and blood coagulation. Easy bruising and bleeding Can interfere with anticoagulant medication
Folic acid Found in many vegetables including, broccoli, peas, asparagus, spinach, green leafy types. Also found in fresh fruit, liver and yeast. Coenzyme needed for production of hemoglobin and formation of DNA. Megaloblastic anemia, spina bifida May mask B12 deficiency
B12 Found in meat, fish, eggs and milk but not in vegetables. Vitamin B12 is needed to make red blood cells. Supplements can help some types of anemia. Pernicious anemia Unknown
B6 (pyridoxine) Found in cereals, yeast, liver, and fish. Vitamin B6 is a coenzyme in amino acid synthesis. Rare to be deficient, convulsions, vomiting, seborrhea, muscular weakness Insomnia, neuropathy
Folic acid and cancer prevention

Women of childbearing age are often encouraged to take a folic acid supplement to help reduce the risk of certain birth defects. Research cited by the Harvard School of Public Health shows that folic acid may have even more benefits, and not just for the developing fetus. Their study shows that people who get more than the recommended amount of folic acid due to diet or supplements can actually lower the risk of developing colon or breast cancer. Since alcohol blocks the absorption of folic acid and inactivates circulating folate, this can be especially important to those who drink alcohol frequently (more than one drink per day). The current recommended intake for folic acid is 400 micrograms per day. There are many excellent sources of folic acid, including prepared breakfast cereals, beans, and fortified grains. So if you would like to reduce your risk of colon or breast cancer, be sure to get more than 400 micrograms per day!

Fat soluble vitamins A, D, E, K

With fat soluble vitamins you need the presence of fat in your diet to absorb them, this is because the bile will not be secreted to help with emulsification and therefore the fat vitamins will not be broken down for absorption. Fat soluble vitamins are stored in organs such as the liver, spleen, and other fatty tissues in the body. Because of this, excessive amounts of fat-soluble vitamins can accumulate in the body resulting in toxicity, but this rarely comes from excessive dietary intake but rather from improper use of vitamin supplements. The other, water-soluble vitamins, do not build up to toxic levels because they are regularly excreted in the urine.

### Minerals

Minerals are atoms of certain chemical elements that are essential for body processes. Minerals are inorganic, meaning that they do not contain the element carbon. They are either produced by our body, or we obtain them by eating certain foods that contain them. They are ions found in blood plasma and cell cytoplasm, such as sodium, potassium, and chloride. In addition, minerals represent much of the chemical composition of bones (calcium, phosphorus, oxygen). They also contribute to nerve and muscle activity (sodium, potassium, calcium). Minerals serve several many other functions as well. There are 21 minerals considered essential for our bodies. Nine of the essential minerals in the body account for less than .01% of your body weight. Because of the small amount of these minerals that our body needs, we call them trace minerals. The 12 most important minerals and their functions are listed below:

Mineral Source Use in the body
Calcium (Ca) Calcium can be found in dairy products, dark green vegetables and legumes. It contributes to bone and teeth formation. In addition, calcium also contributes to nerve and muscle action, and blood clotting.
Chloride (Cl) Chloride is mainly found in table salt. It plays a role in the acid-base balance, stomach acid formation, and body water balance.
Copper (Cu) Copper can be found in seafood, nuts, and legumes. It participates in the synthesis of hemoglobin and melanin.
Fluorine (F) Fluorine is evident in fluoridated water, tea, and seafood. It accounts for the maintenance of teeth, and perhaps the maintenance of bone as well.
Iodine (I) Iodine is a component in iodized salt, marine fish and shellfish. Although a very small amount is needed for our body, according to some, iodine still plays a role in our body's function. It can also be found in seaweed. It is needed for the thyroid hormone.
Iron (Fe) Iron can be found in green leafy vegetables, whole grains foods, legumes, meats, and eggs. It is needed for composition of hemoglobin, myoglobin, and certain enzymes.
Magnesium (Mg) Magnesium is found in whole grains foods, and in green leafy vegetables. It is the coenzyme found in several enzymes.
Phosphorus (P) Phosphorus can be found in meat, poultry, and whole grain foods. It serves as components of bones, teeth, phospholipids, ATP, and nucleic acids.
Potassium (K) Potassium is widespread in the diet, especially in meats and grains. It deals with muscle and nerve function, and also is a major component of intracellular fluid.
Sodium (Na) Sodium is found in table salt, is a major component of water and also widespread in the diet. It participates in the functioning of muscles and nerves.
Sulfur (S) Sulfur is found in meat and diary products. It is a component of many proteins.
Zinc (Zn) Zinc is found in whole grain foods, meats, and seafood. It is a component of many enzymes.

## Nutritional Disorders

Body Mass Index became popular during the early 1980s as obesity started to become a discernible issue in prosperous Western society. BMI provided a simple numeric measure of a person's "fatness" or "thinness", allowing health professionals to discuss the problems of over- and under-weight more objectively with their patients. However, BMI has become controversial because many people, including physicians, have come to rely on its apparent numerical "authority" for medical diagnosis – but that has never been the BMI's purpose. It is meant to be used as a simple means of classifying sedentary (physically inactive) individuals with an average body composition.[1] For these individuals, the current value settings are as follows: a BMI of 18.5 to 25 may indicate optimal weight; a BMI lower than 18.5 suggests the person is underweight while a number above 25 may indicate the person is overweight; a BMI below 15 may indicate the person has an eating disorder; a number above 30 suggests the person is obese (over 40, morbidly obese).

In physiology, the term “weight” is used interchangeably with “mass”. For a given body shape and given density, the BMI will be proportional to weight e.g. if all body weight increase by 50%, the BMI increases by 50%.

BMI is defined as the individual's body weight divided by the square of their height. The formulas universally used in medicine produce a unit of measure that is not dimensionless; it has units of kg/m2. Body mass index may be accurately calculated using any of the formulas below.

 SI units US units UK mixed units $\mathrm{BMI} = \frac{\mathit{weight} \ \mathrm{(kg)}}{\mathit{height}^2 (\mathrm{m^2})}$ $\mathrm{BMI} = 703\cdot \frac{\mathit{weight} \ (\mathrm{lb})}{\mathit{height}^2 \ (\mathrm{in^2})}$ $\mathrm{BMI} = 6.35\cdot \frac{\mathit{weight} \ (\mathrm{stone})}{\mathit{height}^2 \ (\mathrm{m^2})}$
BMI Weight Status
Below 18.5 Underweight
18.5 - 24.9 Normal
25.0 - 29.9 Overweight
30.0 and Above Obese
Either way can be a disorder.

The U.S. National Health and Nutrition Examination Survey of 1994 indicates that 59% of American men and 49% of women have BMIs over 25. Extreme obesity — a BMI of 40 or more — was found in 2% of the men and 4% of the women. There are differing opinions on the threshold for being underweight in females, doctors quote anything from 18.5 to 20 as being the lowest weight, the most frequently stated being 19. A BMI nearing 15 is usually used as an indicator for starvation and the health risks involved, with a BMI <17.5 being one of the criteria for the diagnosis of anorexia nervosa.

Anorexia nervosa: is a psychiatric diagnosis that describes an eating disorder characterized by low body weight and body image distortion with an obsessive fear of gaining weight. Individuals with anorexia often control body weight by voluntary starvation, purging, vomiting, excessive exercise, or other weight control measures, such as diet pills or diuretic drugs. It primarily affects young adolescent girls in the Western world and has one of the highest mortality rates of any psychiatric condition, with approximately 10% of people diagnosed with the condition eventually dying due to related factors.[1] Anorexia nervosa is a complex condition, involving psychological, neurobiological, and sociological components.[2]

Bulimia nervosa: commonly known as bulimia, is generally considered a psychological condition in which the subject engages in recurrent binge eating followed by an intentional purging. This purging is done in order to compensate for the excessive intake of the food and to prevent weight gain. Purging typically takes the form of vomiting; inappropriate use of laxatives, enemas, diuretics or other medication, and excessive physical exercise.

## Metabolism

Absorptive and post absorptive stage of metabolism

The body has two phases to its metabolic cycle. The first is known as the absorptive stage. This stage happens 3-4 hours after a typical meal. During this phase nutrients are absorbed by the body. In other words this is the stage where energy is stored into macromolecules. During the post-absorptive stage the nutrients are not being absorbed instead this is the stage where it is being mobilized.

Insulin

The changes in the body that occur between the absorptive and post-absorptive stages are triggered by the changes in the plasma concentration of insulin. Insulin encourages the synthesis of energy storage molecules. When plasma glucose levels in the bloodstream increase during the absorptive stage, insulin is secreted from the pancreas. When the plasma glucose levels decrease, the post-absorptive phase begins. Insulin acts on several different tissues in the body and influences almost every major aspect of energy metabolism. Insulin supports and promotes all aspects of the absorptive phase by helping store energy in all tissues. It also inhibits the reactions of the post-absorptive phase. Insulin also affects the transport of nutrients across the membrane of ALL body cells except for those located in the liver and CNS. Insulin also has a part in growth where it needs to be present in the blood stream in order for the hormones to effect normally.

Epinephrine and sympathetic nervous activity on metabolism

The sympathetic system and epinephrine suppress insulin and stimulate glucagon secretion. This effects the post absorptive phase by making metabolic adjustments. During the post absorptive phase, plasma glucose levels decrease and cause an increase of glycogen secretion. It also acts directly on glucose receptors in the CNS. This causes a rise in epinephrine secretion by the adrenal medulla. The rise in epinephrine creates a cascade event where the body sends signals to all the tissues (except skeletal muscles) to switch to the post absorptive phase.

## Diabetes

Diabetes Mellitus

Diabetes is essentially any condition which is characterized by an increase in urine production and secretion. The Random House Webster's Unabridged Dictionary defines it as the following... "A disorder of carbohydrate metabolism, usually occurring in genetically predisposed individuals, characterized by inadequate production or utilization of insulin and resulting in excessive amounts of glucose in the blood and urine, excessive thirst, weight loss, and in some cases progressive destruction of small blood vessels leading to such complications as infections and gangrene of the limbs or blindness." In other words, when food is put into the body you get high levels of glucose in your blood stream thus resulting in the release of Insulin to take up and metabolize this glucose. It also stimulates the liver to store the glucose as glycogen, thus resulting in the storage of nutrients and the lowering of glucose levels in the blood. On the flip side you have Glucagon which helps in the breakdown of the stored nutrients when you need them, thus having the opposite effect of Insulin. People who are unable to produce insulin on their own, or are lacking/have damaged their insulin receptors develop what is known as "Diabetes Mellitus." There are two types of Diabetes Mellitus: Type I, aka, Insulin Dependent Diabetes Mellitus (IDDM), and Type II, aka, Non-Insulin Diabetes Mellitus (NIDDM).

Type I diabetes is believed to be an autoimmune disease which has been present since birth or has been brought on by exposure to a virus which causes insulin production by the pancreas to be impaired. This usually results in a person having to receive insulin from an external source. Without this external administration, the body would turn to the metabolism of fat, which leads to the build up of Ketones in the blood, which leads to blood acidosis and could result in a coma or possible death. The onset of Type I diabetes is most commonly seen under the age of 25.

Although Type II Diabetes is like Type I in many ways, it's onset is usually the result of poor lifestyle choices, particularly eating a diet high in sugars and fats while getting little or no physical exercise. Following this routine will quickly lead to damaging or the shutting down of your insulin receptors completely, thus resulting in the lack of glucose storage and the expulsion of essential nutrients from the body via urination. Just like with Type I Diabetes, Type II can have detrimental effects on the body including blindness, kidney disease, atherosclerosis, and again, even lead to the loss of extremities due to gangrene.

Doctors have projected that upwards of seven million Americans may have diabetes, yet many may not know it. If you or someone you know has been suffering from such things as: frequent urination, especially at night; unusual hunger and/or thirst; unexplained weight gain or loss; blurred vision; sores that don't heal; or excessive fatigue then it is highly recommended that you have your fasting blood glucose level checked by a physician. Maintaining an active lifestyle and making sound nutritional choices may greatly extend your life by protecting you from the ills of diabetes.

## Calories, Exercise, and Weight

Energy Balance and Body Weight

Energy is measured in units called calories. A calorie is the amount of energy that is needed to raise the temperature of 1 gram of water by one degree Celsius. Because a calorie is such a small amount, scientists use a larger unit to measure intake, called a kilocalorie. A kilocalorie is also referred to often as a capital "C" Calorie, and is equal to 1000 calories. When we "count" calories, we are actually counting the big Calories.

The old saying, "you are what you eat" is very much true. According to scientists, the average adult consumes 900,000 calories per year. Most people tend to take in more calories than their body needs. An intake of 120 extra calories a day, or around 5% excess in calories, yields an annual increase of 12 extra pounds of body weight. The more developed countries tend to consume more calories than others because of the increasing availability and dieting habits of eating refined foods with little nutrition in them and lots of saturated fat. In our society, there is a huge emphasis put on a person's image and how thin they are, and less emphasis put on what's most important--the nutrition our body receives. While our body do need calories every day to keep us going, we need to watch the amount of calories we consume in order to maintain good health and proper body weight.

Our Caloric intake is linked directly to our health status. Being overweight is generally defined as being 15-20% above ideal body weight, while obesity is defined as being more than 20% above it. People who weigh 10% less than ideal are considered underweight. This is less common in the more developed countries. In less developed countries such as South Africa, being underweight is quite common because they lack the nutrition to maintain good health.

How do we gain weight? When we consume more calories than our body can burn in a day, the excess energy is stored in specialized cells as fat. It is also important to know that the three classes of nutrients have different Caloric contents. Carbohydrates and proteins contain only four Calories per gram, while fat contains about nine. Because of this, it is essential that we watch our amount of fat intake. If we continuously feed our body more calories than is needed, our body will produce more fat cells, to store the excess energy. This contributes to gaining weight.

It is more difficult for chronically overweight persons to lose weight than normal-weight persons. This is because they are constantly fighting the body's own weight-control system, which responds as if the excess weight were normal. Our body is capable of measuring how much we intake, and maintaining our weight. When an overweight person goes on a diet, and consumes less calories, their body will respond as if they are starving, and try to save energy where it can to make up for the decrease in received calories.

Exercise is a great way to maintain healthy body weight.

Maintaining a healthy body weight

To maintain a stable body weight, our consumption of calories needs to be equal to the amount of calories we use in a day. You can determine your daily energy needs by determining your basal metabolic rate (BMR). Your BMR is the energy your body needs to perform essential activities. Some examples of essential activities are breathing, and maintaining organ function. Your metabolic rate can be influenced by your age, gender, muscular activity, body surface area and environmental temperature.

Physical Activity: An efficient way to use calories

Although the BMR stays about the same, we can dramatically change the amount of calories we burn in a day by participating in physical activity. It is important to note that heavier people do more work per hour than normal-weight people, for the same level of activity. We must spend about 3,500 Calories to lose one pound of fat. The best approach to weight loss, recommended by nutritionists, is to reduce the Caloric intake by a small amount each day while gradually increasing your amount of physical activity.

BMR: Determining how many calories we need

There are several factors that influence the BMR. Each person's body has different needs. BMR needs vary with gender and body composition. Muscle tissue consumes more energy than fat tissue. Typically, males need more calories than females, because they generally have more muscle tissue. Males use up calories faster than women. BMR also varies with your age as well. As we age, our body needs less and less calories. In addition, some health conditions can contribute to our needed calories. Health conditions such as fever, infections, and hyperthyroidism are examples of health conditions that lower your BMR. Our stress level effects our needed calorie intake as well. So does our increase or decrease in consumption, and our rate of metabolism, which varies with individual genetics.

Here are the steps to determining your BMR, or, the amount of energy your body needs to perform essential activities:

1. First calculate your weight into kilograms. This is obtained by dividing the number of pounds by 2.2.

2. For Males: multiply your weight in kilograms by 1.0. For Females: multiply your weight in kilograms by 0.9.

3. This number approximates the number of Calories you consumer per hour. Now multiply this number by 24 to estimate how many Calories you need per day to support basic metabolic functions.

4. The end result is your personal basal metabolic rate!

Exercise

Living a healthy, well-balanced life involves good nutrition and adequate exercise. They work hand in hand.

• There are many benefits to exercising.
• Your chances of living longer increases.
• You decrease your chances of getting diseases such as:
• Heart disease or problems with circulation
• Many types of cancer
• Type 2 diabetes
• Arthritis
• Osteoporosis
• Depression
• Anxiety
• Controls weight
• The costs of being physically active far outweigh the medical costs for those who are not physically active.
• Cardiovascular Exercise
• Thirty minutes a day of moderate intensity exercise or physical activity has been shown to make noticeable increases in breathing and heart rate.
• METs (metabolic equivalents) are the amount of energy it takes while at rest (1 calorie per every 2.2 pounds of body weight per hour). Moderate intensity activities can get you to burn energy 3-6 times more depending upon the activity.
• Walking is ideal for everyone.
• The MET scale chart on the Harvard School of Public Health web site is interesting.
• Feeling what’s right
• A study suggests that those with disabilities, who are older, or who are out of shape get the same benefit from 30 minutes of lower intensity exercise as those who are younger and more fit do from more intense activity.
• Beyond the heart
• There are other areas that benefit from different types of exercise such as strength training. These types of exercises help balance, muscle strength, and overall function.
• Resistance or strength training can possibly decrease the loss of lean muscle tissue and even replace some already lost.
• It can also decrease fat mass and increase resting metabolic rate.
• It is effective in fighting osteoporosis.
• It also helps maintain functional tasks in older populations.
• Flexibility training or stretching exercises increases range of motion, decrease soreness, and injury.

## Glossary

Amino acids
The building blocks of protein in the body. There are nine essential amino acids that are not manufactured by the body and must come from the diet.
Anabolism
Refers the cumulative metabolic intracellular, molecular processes by which every cell repairs itself and grows.(synthesizing).
Anorexia
A common eating disorder characterized by an abnormal loss of the appetite for food
antioxidants
Compounds that protect against cell damage inflicted by molecules called oxygen-free radicals, which are a major cause of disease and aging.
Bulimia Nervosa
Eating disorder characterized by binge eating followed by an intentional purging.
Catabolism
The opposite of Anabolism. The metabolic process that breaks down molecules into smaller units. It is made up of degradative chemical reactions in the living cell.
Cirrhosis of the liver
An irreversible advanced scarring of the liver as a result of chronic inflammation of the liver. Can be caused by alcoholism or obesity.
Complete Proteins
Proteins that contain ample amounts of all of the essential amino acids
Deamination
When an amino acid group breaks off an amino acid that makes a molecule of ammonia and ketoacid.
Diverticulosis
A diet low in dietary fiber increases the risk, this is the pouches called diverticula formation on the outer portion of the large intestine.
Gastric Bypass Surgery
An operation where a small gastric pouch is created and the remainder of the stomach bypassed
Incomplete Proteins
Proteins that contain some but not all of all of the essential amino acids required by the body
Ipecac
A drug used to induce vomiting
Kwashiorkor
A childhood form of malnutrition caused by general lack of protein or deficiency in one or more amino acids. Appearance of a person with this is a swollen belly due to inadequate production of albumin, which causes the blood to have a lower osmotic pressure, resulting in more fluids escaping from the plasma.
Marasmus
malnutrition cause by a lack of kilocalorie intake. Appearance of a person with this is a skeletal one.
Malnutrition
An imbalanced nutrient and or energy intake.
Obesity
A condition in which the natural energy reserve in fatty tissue increased to a point where it is thought to be a risk factor for certain health conditions or increased mortality
Peptide
Two or more amino acids linked together by a bond called a peptide bond.
Polypeptide
A string of amino acids linked together by peptide bonds. A protein is an example of a polypeptide.
Starvation
A severe reduction in vitamin, nutrient, and energy intake, and is the most extreme form of malnutrition

## Review Questions

Answers for these questions can be found here

1. Nonessential amino acids

A) are stored in the body
B) are only needed occasionally
C) can be produced in the body
D) can be taken in supplements

2. Micronutrients include

A) minerals and vitamins
B) lipids and fatty acids
C) amino acids and proteins
D) vitamins and minerals

3. The body requires amino acids to

A) produce new red blood cells
B) produce new protein
C) replace damaged red blood cells
D) replace damaged protein
E) A and C
F) B and D

4. The function of lipids

A) store energy
B) organ protection
C) temperature regulator
D) emulsifiers
E) all of the above

5. This vitamin is a vital component of the reproductive process and lowers the risk of getting cancer

A) B12
B) Folic Acid
C) Niacin
D) Thiamine
E) Retinol

6. This vitamin is needed to make red blood cells

A) B1
B) B2
C) B6
D) B12

7. This participates in the synthesis of hemoglobin and melanin

A) Copper
B) Chloride
C) Calcium
D) Iron
E) Iodine

8. I go to visit my grandmother and see that she has multiple bruises- from this I may assume that

A) she has a vitamin A deficiency
B) she is old and just clumsy
C) she has a vitamin K deficiency
D) she has scurvy
E) she has rickets

9. As a pirate I may get scurvy because

A) I am not getting enough vegetables on the ship
B) I am not getting enough fruit on the ship
C) I am eating too much fish on the ship
D) I am getting too much sun on the ship
E) I am drinking too much rum on the ship

10. I am taking anticoagulant medication and it doesn’t seem to be working, this could be because

A) I have too much vitamin A
B) I have too much B12
C) I have too much sodium
D) I have too much vitamin E
E) I have too much vitamin K

11. Which of these are fat soluble?

A) Vitamin K
B) Vitamin E
C) Vitamin D
D) Vitamin A
E) All of the above

## References

• Van De Graaff (2002) Human Anatomy 6th ed. McGraw-Hill Higher Education
• Windmaier, P.W. Raff, H. Strang, T.S. (2004) Vander, Sherman, & Luciano's Human Physiology, the Mechanisms of Body Function 9th ed. Mcgraw-Hill
• Starr & McMillan (2001) Human Biology 6th ed. Thomson-Brooks/cole.
• Spurlock, Morgan (2004) Super Size Me Hart Sharp Video
• Sylvia S. Mader (2006) Human Biology 9th ed. McGraw-Hill Higher Education
• Anatomy & Physiology Revealed (2007) McGraw-Hill Higher Education
• Random House Webster's Unabridged Dictionary 2nd ed. (2001) Random House