Chapter 6

oligopeptides

joining of four to nine amino acids

RDA for the amount of protein required for nearly all adults to maintain protein equilibrium

- 0.8 gram of protein per kilogram of healthy body weight. - Requirements are higher during periods of growth, such as pregnancy and infancy - an increased protein intake of more than 1.0 grams per kilogram of body weight per day has been recommended for older adults as a result of the PROT-AGE Study - 56 grams of protein daily for a typical 70-kilogram (154-pound) man - about 46 grams of protein daily for a typical 57-kilogram (125-pound) woman. - Researchers now recommend that adults consume at least 30 grams of protein at more than one meal in order to maintain healthy muscles and bones.

Nuts & seeds

- 1-ounce serving of nuts or seeds generally supplies 160 to 190 kcal, 6 to 10 grams of protein, and 14 to 19 grams of fat. - Although they are a dense source of calories, nuts and seeds make a powerful contribution to health when consumed in moderation.

Vegan health concerns

- At the forefront of nutritional concerns are riboflavin, vitamin B-12, iron, zinc, iodine, calcium, and vitamin D. - Riboflavin can be obtained from green leafy vegetables, whole grains, yeast, and legumes—components of most vegan plans. - Vitamin B-12 only occurs naturally in animal foods. Vegans can prevent a vitamin B-12 deficiency by finding a reliable source of this vitamin, such as fortified soybean milk, ready-to-eat breakfast cereals, and special nutritional yeast grown on media rich in vitamin B-12. Plants can contain soil or microbial contaminants that provide trace amounts of vitamin B-12, but these are negligible sources of the vitamin. - For iron, the vegan can consume whole grains and ready-to-eat breakfast cereals, dried fruits and nuts, and legumes. The iron in these foods is not absorbed as well as iron in animal foods, but consuming these foods with a good source of vitamin C can enhance iron absorption. Cooking in cast iron. -

negative protein balance

- Consuming less protein than needed - such as when acute illness reduces the desire to eat, causing a person to lose more protein than he or she consumes.

Red and processed meat

- Eating patterns rich in animal products are most likely low in beneficial substances found in plant sources, including fiber, some vitamins (e.g., folate), some minerals (e.g., magnesium), and phytochemicals, and are high in substances such as saturated fat. - shown to be associated with increased risk of kidney disease and cardiovascular disease

Plant Proteins

Per gram of protein, plant foods provide more magnesium, fiber, folate, vitamin E, iron (absorption is increased by the vitamin C also present), and zinc than animal sources of protein, and some calcium

Specific proteins required for

blood clotting fluid balance hormone and enzyme production visual processes transport of many substances in the bloodstream cell repair require specific proteins

protein-calorie malnutrition (PCM)

consuming too few calories as protein

Proteins are crucial for

regulation and maintainance

Which of the following is true about pepsin?

Acid activates pepsin in the stomach.

Protein Functions

- Producing vital body structures - Maintaining fluid balance (osmotic pressure/edema) - Acid/base balance (buffers) - Forming hormones & enzymes - Contributing to immune fn - Forming glucose (In an extreme situation, however, such as in starvation, amino acids from muscle tissue are regularly converted into glucose, which wastes muscle tissue and can produce edema.) - Providing energy (Under most conditions, cells primarily use fats and carbohydrates for energy needs.) - Contribute to satiety (Compared to the other macronutrients, proteins provide the highest feeling of satiety after a meal. Many experts warn against skimping on protein when trying to reduce energy intake to lose weight. Meeting protein needs is still important, and exceeding needs somewhat may provide an additional benefit when dieting to lose weight. - Supplies readily available Nitrogen

Vegetarianism

- Studies show that death rates from some chronic diseases, such as certain forms of cardiovascular disease, hypertension, many forms of cancer, type 2 diabetes, and obesity, are lower for vegetarians than for nonvegetarians. - Vegetarians often live longer, as shown in religious groups that practice vegetarianism - nearly 70% of the grain crop is used for animal feed, and globally 35% of the grain harvest is used to produce animal protein. 3 kg grain for 1 kg meat - Lactovegetarians, ovovegetarians, lactoovovegetarians, pescovegetarians

limiting amino acid

- The essential amino acid in smallest supply in a food or meal in relation to body needs becomes the limiting factor - it limits the amount of protein the body can synthesize. - Typically, 50% of the amino acids in dietary proteins are essential. - adults need only about 11% of their total protein requirement to be supplied by essential amino acids. - estimated requirements for essential amino acids for infants and preschool children are greater (40% of total protein intake) because of the needs of rapid growth and development; however, in later childhood, the need drops to 20%.

Protein in the North American diet

- The top five contributors have traditionally been beef, poultry, milk, white bread, and cheese. - Food consumption surveys have revealed, however, a steady drop in U.S. meat and poultry consumption. - According to the USDA, the average American consumed 202 pounds of red meat and poultry in 2014, 8% less than in 2004. - This decrease was primarily related to a sharp drop in beef consumption. - In 2014, the U.S. beef consumption per person of 54.2 pounds, was down 18% from 10 years ago and down about 30% from 1980. - The downward trend seems to be a result of the rising cost of beef as well as conscious decisions to eat less red meat for health, environmental, and social reasons.

Marasmus

- Victims have a "skin-and-bones" appearance, with little or no subcutaneous fat -

complementary proteins.

- When two or more protein sources are combined in a meal or snack to compensate for deficiencies in their essential amino acid contents - legumes and grains, such as beans and rice - vegetables, which are limited in methionine, can be combined with nuts, which are limited in lysine - need not be consumed at the same meal

phenylketonuria (PKU)

- a genetic disorder in which a nonessential amino acid becomes conditionally essential. - A person with PKU has a limited ability to metabolize the essential amino acid phenylalanine. - Normally, the body uses an enzyme to convert much of our dietary phenylalanine intake into tyrosine. - In PKU-diagnosed persons, the activity of the enzyme used in processing phenylalanine to tyrosine is insufficient. - The results are that (1) tyrosine becomes essential (it must be obtained from the diet); whereas (2) phenylalanine from the diet builds up to toxic levels in the blood. - Elevated phenylalanine disrupts brain function, leading to mental retardation. - PKU is treated with a special diet that limits phenylalanine

Legumes

- a plant family with pods that contain a single row of seeds. - ½-cup serving of legumes provides 100 to 150 kcal, 5 to 10 grams of protein, less than 1 gram of fat, and about 5 grams of fiber. - Gas production can be decreased by soaking dry beans in water to leach the indigestible carbohydrates into the water, which then can be disposed.

protein turnover

- a process by which a cell can respond to its changing environment by making proteins that are needed and disassembling proteins that are not needed. - Excess protein in the diet does not enhance the synthesis of these body components, but eating too little protein can prevent it. - Most vital body proteins are in a constant state of breakdown, rebuilding, and repair. - During a 24-hour period, an adult turns over (makes and degrades) about 250 grams of protein, recycling many of the amino acids. - Relative to the 65 to 100 grams of protein typically consumed by adults in North America, recycled amino acids make an important contribution to total protein metabolism.

Kwashiorkor

- a word from Ghana that means "the disease that the first child gets when the new child comes." - The major symptoms of kwashiorkor are apathy, diarrhea, listlessness, failure to grow and gain weight, and withdrawal from the environment. - changes in hair color, potassium deficiency, flaky skin, fatty liver, reduced muscle mass, and massive edema in the abdomen and legs. The presence of edema in a child who has some subcutaneous fat (i.e., fat directly under the skin) is the hallmark of kwashiorkor

conditionally essential amino acids.

- amino acids that are normally considered nonessential but become essential under certain circumstances (rapid growth, disease, or metabolic stress) when the body's need for them exceeds the ability to produce them - Arginine and glutamine are two examples

High/Low quality proteins

- are those that are readily digestible and contain the essential amino acids in quantities that human require. - animal proteins (except gelatin) are considered high-quality (also called complete) proteins, which contain sufficient amounts of the nine essential amino acids. - The majority of individual plant sources of proteins are considered lower-quality (also called incomplete) proteins because their amino acid patterns can be quite different from ours.

enzymatic digestion of protein

- begins in the stomach - Proteins are first denatured by stomach acid. - Pepsin, a major stomach enzyme for digesting proteins, then goes to work on the unraveled polypeptide chains. Pepsin breaks the polypeptide into shorter chains of amino acids because it can break only a few of the many peptide bonds found in these large molecules. - The release of pepsin is controlled by the hormone gastrin. - Thinking about food or chewing food stimulates gastrin release in the stomach. Gastrin then stimulates the stomach to produce acid and release pepsin. - Once in the small intestine, the partially digested proteins (and any fats accompanying them) trigger the release of the hormone cholecystokinin (CCK) from the walls of the small intestine. - CCK, in turn, travels through the bloodstream to the pancreas, where it causes the pancreas to release protein-splitting enzymes, such as trypsin. - These digestive enzymes further divide the chains of amino acids into segments of two to three amino acids and some individual amino acids. - Eventually, this mixture is digested into amino acids, using other enzymes from the lining of the small intestine and enzymes present in the absorptive cells themselves.

Amino acids

- compounds that serve as the building blocks for proteins. They are chemically unique in that they contain nitrogen along with carbon, oxygen, and hydrogen - There are 20, - 9 are essential: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine - 11 are nonessential: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine - Each amino acid has an "acid" group, an "amino" group, and a "side" or R group specific to the amino acid. - Sources: Animal sources of protein, such as meat and dairy products, and plant sources of protein, such as beans, nuts, and seeds

Allergies

- food allergies occur in up to 8% of children 4 years of age or younger and in up to 2% of adults. - Eight foods account for 90%: soy, peanuts, tree nuts, wheat, milk, eggs, fish, and shellfish

peptide bonds

- form btw amino acids to form proteins - form between the amino group of one amino acid and the acid (carboxyl) group of another.

polypeptides

- joining of 10 or more amino acids - Most proteins are polypeptides ranging from about 50 to 2000 amino acids.

branched-chain amino acids

- leucine, isoleucine, and valine. - The branched-chain amino acids are the primary amino acids that promote and signal protein synthesis and turnover in muscles. - Whey protein (from milk) is popular among strength-training athletes because it is particularly rich in branched-chain amino acids

positive protein balance

- necessary when a body is growing or recovering from an illness or injury - To achieve this, a person must eat more protein daily than he or she loses. - the hormones insulin, growth hormone, and testosterone all stimulate positive protein balance. Resistance exercise (weight training) also enhances positive protein balance.

Sickle cell disease (also called sickle cell anemia)

- one example of a genetic disease in which amino acids are out of order on a protein. - In North America, people of African descent are especially prone to this genetic disease. - Sickle cell anemia is not a nutritional disease but is caused by a mutation in the genetic code for hemoglobin. The mutation causes the amino acid glutamic acid to be replaced with the amino acid valine. - Sickle red blood cells become hard and sticky, which causes them to clog blood flow and break apart. - This can cause severe bone and joint pain, abdominal pain, headache, convulsions, paralysis, and even death due to the lack of oxygen.

Absorption of proteins

- taken up by active transport into the absorptive cells lining the small intestine. - Any remaining peptide bonds are broken inside intestinal cells to yield individual amino acids. - amino acids are water-soluble and so travel to the liver via the portal vein - In the liver, individual amino acids can undergo several modifications, depending on the needs of various body tissues. Individual amino acids may be (1) combined into the proteins needed by specific cells (2) broken down for energy needs (3) released into the bloodstream (4) converted into nonessential amino acids, glucose, or fat. With excess protein intake, amino acids are converted into fat as a last resort. - Except during infancy, it is uncommon for intact proteins to be absorbed from the digestive tract. - In infants up to 4 to 5 months of age, the gastrointestinal tract is somewhat permeable to small proteins, so some whole proteins can be absorbed.

Acceptable Macronutrient Distribution Range for protein

10% to 35%

Amino Acid Supplements

The amino acids methionine, cysteine, and histidine are most likely to cause toxicity when consumed in large amounts. - Due to this potential for imbalances and toxicities, the best advice to ensure adequacy is to stick to whole foods as sources of amino acids rather than supplements. - Amino acid supplements also have a disagreeable odor and flavor and are much more expensive than food protein.

Denaturation

The process of altering a proteins 3-D structure by Exposure to acid or alkaline substances, heat, or agitation

When there is a need for increased dietary protein during pregnancy or lactation, which of the following foods would be least desirable?

gelatin

A child with marasmus

is very susceptible to infections.

tripeptides

joining of three amino acids

dipeptides

joining of two amino acids

Undernutrition

marasmus is worse than kwashiorkor