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Protein intake

Human nutrition
Journal of the American Dietetic Association. But they objected, preferring vegetables pulses and water in accordance with their Jewish dietary restrictions. However, more practical, albeit less accurate, methods are often used, such as anthropometry , in which subcutaneous fat at various sites is measured using skinfold calipers; bioelectrical impedance, in which resistance to a low-intensity electrical current is used to estimate body fat; and near infrared interactance, in which an infrared light aimed at the biceps is used to assess fat and protein interaction. Krausw's Food and the Nutrition Care Process 13th ed. New York, New York: Identify deficiency and toxicity symptoms for vitamin C, folate, vitamin A, niacin and B12, among others.

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Nutrition 101: Science of Nutrition

Types of soluble fibre are gums, pectins , some hemicelluloses, and mucilages; fruits especially citrus fruits and apples , oats, barley, and legumes are major food sources. Both soluble and insoluble fibre help delay glucose absorption, thus ensuring a slower and more even supply of blood glucose. Dietary fibre is thought to provide important protection against some gastrointestinal diseases and to reduce the risk of other chronic diseases as well. Lipids also contain carbon, hydrogen, and oxygen but in a different configuration, having considerably fewer oxygen atoms than are found in carbohydrates.

Lipids are soluble in organic solvents such as acetone or ether and insoluble in water, a property that is readily seen when an oil-and-vinegar salad dressing separates quickly upon standing. The lipids of nutritional importance are triglycerides fats and oils , phospholipids e. Lipids in the diet transport the four fat-soluble vitamins vitamins A, D, E, and K and assist in their absorption in the small intestine.

They also carry with them substances that impart sensory appeal and palatability to food and provide satiety value, the feeling of being full and satisfied after eating a meal. Fats in the diet are a more concentrated form of energy than carbohydrates and have an energy yield of 9 kilocalories per gram. Adipose fatty tissue in the fat depots of the body serves as an energy reserve as well as helping to insulate the body and cushion the internal organs.

The major lipids in food and stored in the body as fat are the triglycerides, which consist of three fatty acids attached to a backbone of glycerol an alcohol.

They are classified as saturated or unsaturated according to their chemical structure. A point of unsaturation indicates a double bond between two carbon atoms, rather than the full complement of hydrogen atoms that is present in saturated fatty acids. A monounsaturated fatty acid has one point of unsaturation, while a polyunsaturated fatty acid has two or more. The common fatty acids in foods are listed in the table.

Fatty acids found in the human diet and in body tissues range from a chain length of 4 carbons to 22 or more, each chain having an even number of carbon atoms.

Of particular importance for humans are the carbon polyunsaturated fatty acids alpha-linolenic acid an omega-3 fatty acid and linoleic acid an omega-6 fatty acid ; these are known as essential fatty acids because they are required in small amounts in the diet. The omega designations also referred to as n-3 and n-6 indicate the location of the first double bond from the methyl end of the fatty acid. Other fatty acids can be synthesized in the body and are therefore not essential in the diet.

About a tablespoon daily of an ordinary vegetable oil such as safflower or corn oil or a varied diet that includes grains, nuts , seeds , and vegetables can fulfill the essential fatty acid requirement. Essential fatty acids are needed for the formation of cell membranes and the synthesis of hormone -like compounds called eicosanoids e.

The consumption of fish once or twice a week provides an additional source of omega-3 fatty acids that appears to be healthful. A fat consisting largely of saturated fatty acids, especially long-chain fatty acids, tends to be solid at room temperature; if unsaturated fatty acids predominate, the fat is liquid at room temperature.

Fats and oils usually contain mixtures of fatty acids, although the type of fatty acid in greatest concentration typically gives the food its characteristics. Butter and other animal fats are primarily saturated; olive and canola oils, monounsaturated; and fish, corn , safflower , soybean, and sunflower oils, polyunsaturated. Although plant oils tend to be largely unsaturated, there are notable exceptions, such as coconut fat , which is highly saturated but nevertheless semiliquid at room temperature because its fatty acids are of medium chain length 8 to 14 carbons long.

Saturated fats tend to be more stable than unsaturated ones. The food industry takes advantage of this property during hydrogenation , in which hydrogen molecules are added to a point of unsaturation, thereby making the fatty acid more stable and resistant to rancidity oxidation as well as more solid and spreadable as in margarine.

However, a result of the hydrogenation process is a change in the shape of some unsaturated fatty acids from a configuration known as cis to that known as trans. Trans -fatty acids, which behave more like saturated fatty acids, may also have undesirable health consequences. A phospholipid is similar to a triglyceride except that it contains a phosphate group and a nitrogen -containing compound such as choline instead of one of the fatty acids.

In food, phospholipids are natural emulsifiers , allowing fat and water to mix, and they are used as food additives for this purpose. In the body, phospholipids allow fats to be suspended in fluids such as blood , and they enable lipids to move across cell membranes from one watery compartment to another. The phospholipid lecithin is plentiful in foods such as egg yolks, liver, wheat germ, and peanuts. However, the liver is able to synthesize all the lecithin the body needs if sufficient choline is present in the diet.

Sterols are unique among lipids in that they have a multiple-ring structure. The well-known sterol cholesterol is found only in foods of animal origin—meat, egg yolk , fish , poultry , and dairy products. There are a number of sterols in shellfish but not as much cholesterol as was once thought. Cholesterol is essential to the structure of cell membranes and is also used to make other important sterols in the body, among them the sex hormones, adrenal hormones , bile acids, and vitamin D.

However, cholesterol can be synthesized in the liver , so there is no need to consume it in the diet. Cholesterol-containing deposits may build up in the walls of arteries, leading to a condition known as atherosclerosis , which contributes to myocardial infarction heart attack and stroke. Furthermore, because elevated levels of blood cholesterol, especially the form known as low-density lipoprotein LDL cholesterol, have been associated with an increased risk of cardiovascular disease , a limited intake of saturated fat—particularly medium-chain saturated fatty acids, which act to raise LDL cholesterol levels—is advised.

Trans-fatty acids also raise LDL cholesterol, while monounsaturated and polyunsaturated cis fats tend to lower LDL cholesterol levels. The complex relationships between various dietary lipids and blood cholesterol levels, as well as the possible health consequences of different dietary lipid patterns, are discussed in the article nutritional disease.

Proteins , like carbohydrates and fats, contain carbon, hydrogen, and oxygen, but they also contain nitrogen , a component of the amino chemical group NH 2 , and in some cases sulfur.

Proteins serve as the basic structural material of the body as well as being biochemical catalysts and regulators of genes. Aside from water, protein constitutes the major part of muscles, bones, internal organs, and the skin , nails , and hair.

Protein is also an important part of cell membranes and blood e. Enzymes , which catalyze chemical reactions in the body, are also protein, as are antibodies , collagen in connective tissue, and many hormones, such as insulin. Tissue proteins are in a dynamic equilibrium with proteins in the blood, with input from proteins in the diet and losses through urine , feces , and skin. In a healthy adult, adjustments are made so that the amount of protein lost is in balance with the amount of protein ingested.

However, during periods of rapid growth, pregnancy and lactation , or recuperation after illness or depletion, the body is in positive nitrogen balance, as more protein is being retained than excreted. The opposite is true during illness or wasting, when there is negative nitrogen balance as more tissue is being broken down than synthesized. Each gene makes one or more proteins, each with a unique sequence of amino acids and precise three-dimensional configuration. Amino acids are also required for the synthesis of other important nonprotein compounds, such as peptide hormones, some neurotransmitters , and creatine.

Food contains approximately 20 common amino acids, 9 of which are considered essential, or indispensable, for humans; i. The essential amino acids for humans are histidine , isoleucine , leucine , lysine , methionine , phenylalanine , threonine , tryptophan , and valine.

Conditionally indispensable amino acids include arginine , cysteine , and tyrosine , which may need to be provided under special circumstances, such as in premature infants or in people with liver disease, because of impaired conversion from precursors.

The relative proportions of different amino acids vary from food to food see table. Foods of animal origin— meat , fish , eggs , and dairy products —are sources of good quality, or complete, protein; i. Gelatin , which lacks the amino acid tryptophan , is an exception. Individual foods of plant origin, with the exception of soybeans , are lower quality, or incomplete, protein sources.

Lysine , methionine , and tryptophan are the primary limiting amino acids; i. However, a varied vegetarian diet can readily fulfill human protein requirements if the protein-containing foods are balanced such that their essential amino acids complement each other. For example, legumes such as beans are high in lysine and low in methionine, while grains have complementary strengths and weaknesses.

Thus, if beans and rice are eaten over the course of a day, their joint amino acid patterns will supplement each other and provide a higher quality protein than would either food alone. Traditional food patterns in native cultures have made good use of protein complementarity.

However, careful balancing of plant proteins is necessary only for those whose protein intake is marginal or inadequate. In affluent populations, where protein intake is greatly in excess of needs, obtaining sufficient good quality protein is usually only a concern for young children who are not provided with animal proteins.

The World Health Organization recommends a daily intake of 0. Thus, a kg pound man would need This recommendation, based on nitrogen balance studies, assumes an adequate energy intake. Infants, children, and pregnant and lactating women have additional protein needs to support synthesis of new tissue or milk production. Protein requirements of endurance athletes and bodybuilders may be slightly higher than those of sedentary individuals, but this has no practical significance because athletes typically consume much more protein than they need.

During conditions of fasting , starvation , or insufficient dietary intake of protein, lean tissue is broken down to supply amino acids for vital body functions. Persistent protein inadequacy results in suboptimal metabolic function with increased risk of infection and disease. Vitamins are organic compounds found in very small amounts in food and required for normal functioning—indeed, for survival.

Humans are able to synthesize certain vitamins to some extent. For example, vitamin D is produced when the skin is exposed to sunlight ; niacin can be synthesized from the amino acid tryptophan; and vitamin K and biotin are synthesized by bacteria living in the gut. However, in general, humans depend on their diet to supply vitamins.

When a vitamin is in short supply or is not able to be utilized properly, a specific deficiency syndrome results. When the deficient vitamin is resupplied before irreversible damage occurs, the signs and symptoms are reversed. The amounts of vitamins in foods and the amounts required on a daily basis are measured in milligrams and micrograms.

Unlike the macronutrients, vitamins do not serve as an energy source for the body or provide raw materials for tissue building. Rather, they assist in energy-yielding reactions and facilitate metabolic and physiologic processes throughout the body.

Vitamin A , for example, is required for embryonic development, growth, reproduction, proper immune function, and the integrity of epithelial cells, in addition to its role in vision. The B vitamins function as coenzymes that assist in energy metabolism; folic acid folate , one of the B vitamins, helps protect against birth defects in the early stages of pregnancy.

Vitamin C plays a role in building connective tissue as well as being an antioxidant that helps protect against damage by reactive molecules free radicals. Now considered to be a hormone , vitamin D is involved in calcium and phosphorus homeostasis and bone metabolism. Vitamin E , another antioxidant, protects against free radical damage in lipid systems, and vitamin K plays a key role in blood clotting. Although vitamins are often discussed individually, many of their functions are interrelated, and a deficiency of one can influence the function of another.

Vitamin nomenclature is somewhat complex, with chemical names gradually replacing the original letter designations created in the era of vitamin discovery during the first half of the 20th century. Nomenclature is further complicated by the recognition that vitamins are parts of families with, in some cases, multiple active forms.

Some vitamins are found in foods in precursor forms that must be activated in the body before they can properly fulfill their function. The 13 vitamins known to be required by human beings are categorized into two groups according to their solubility.

The four fat-soluble vitamins soluble in nonpolar solvents are vitamins A, D, E, and K. Although now known to behave as a hormone, the activated form of vitamin D, vitamin D hormone calcitriol , is still grouped with the vitamins as well. The nine water-soluble vitamins soluble in polar solvents are vitamin C and the eight B-complex vitamins: Choline is a vitamin-like dietary component that is clearly required for normal metabolism but that can be synthesized by the body.

Although choline may be necessary in the diet of premature infants and possibly of those with certain medical conditions, it has not been established as essential in the human diet throughout life. Different vitamins are more or less susceptible to destruction by environmental conditions and chemical agents.

For example, thiamin is especially vulnerable to prolonged heating, riboflavin to ultraviolet or fluorescent light, and vitamin C to oxidation as when a piece of fruit is cut open and the vitamin is exposed to air. In general, water-soluble vitamins are more easily destroyed during cooking than are fat-soluble vitamins. Check out this page for more information on Study. Pre-Exam Checklist Before taking the exam, all of the following requirements must be met: A College Accelerator Study.

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This card has been declined. Please use a different card. Prepaid cards not accepted. Expiration is not a valid, future date. Year Expiration Year is required. Zip Code Zip code is required. Lesson 1 - What is Nutrition? Lesson 2 - Energy-Yielding Nutrients: Lesson 3 - Organic vs Inorganic Nutrients: Lesson 5 - Dietary Reference Intakes: How to Avoid Disease. Lesson 1 - Healthy Diet Planning Guidelines: Lesson 3 - What Drives Us to Eat?

Lesson 4 - Factors that Influence Dietary Choices: Lesson 6 - The American Diet: Lesson 7 - Determining Your Nutritional Needs.

Lesson 8 - Calories: Lesson 9 - How to Read Food Labels: Lesson 10 - Making Healthy Nutritional Choices: Lesson 1 - Structure and Function of Carbohydrates.

Lesson 2 - What Are Carbohydrates? Lesson 3 - The Importance of Carbohydrates: Lesson 4 - Lactose Intolerance and the Major Disaccharides: Lesson 5 - Regulation of Blood Glucose: Lesson 7 - Insoluble and Soluble Fiber: Lesson 1 - Structure and Function of Lipids.

Lesson 2 - Lipids: Lesson 4 - Lipoproteins: Lesson 6 - Recommended Dietary Intakes of Lipids. Lesson 7 - Health Effects Associated with Lipids. Lesson 4 - Primary Functions of Protein in the Body.

Lesson 5 - Proteins: Lesson 7 - Health Effects Associated with Proteins. Lesson 1 - Water's Role as a Nutrient: Lesson 2 - Water Balance in the Body: Lesson 1 - Classification of Minerals: Lesson 3 - Minerals in Our Food: Lesson 5 - Mineral Supplements: Lesson 3 - Copper: Lesson 5 - Selenium: Lesson 7 - Chromium: Lesson 9 - Iron: Lesson 10 - Zinc: Lesson 11 - Iodine: Lesson 12 - Fluoride: Lesson 13 - Manganese: Moving from the histology of skeletal muscle, now we need to know about cardiac muscle tissues and smooth muscle tissue.

This is Lesson 3 in our Muscular System series. This is part of our Anatomy and Physiology lecture series. From YouTube , produced by m. Welcome to the Muscular System! In this video we look at the histology of skeletal muscle tissue and the functions of skeletal muscle. This is Lesson 1 in our Muscular System series. In this video we take a look at the types of muscle contractions: We also cover the relationship muscles have with each other, specifically the agonist, synergists, antagonist, and fixator.

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