chapter 4 proteins

dietary reference intakes

RDA's suggest 10-35% caloric intake from protein

Positive nitrogen balance exists during period of rapid growth (infancy and adolescence)

TRUE

egg protein has a higher biologic value than meat protein

TRUE

healthy adults are in a state of nitrogen balance

TRUE

the primary function of dietary protein is to supply the necessary amino acids to build and repair body tissue

TRUE

when negative nitrogen balance exists, an individual is less able to resist infection and general health deteriorates

TRUE

protein efficiency ration (PER)

based on the weight gain of a growing test animal in relation to its protein intake

stomach

beginning of chemical digestion of proteins. the stomachs chief digestive function overall is the first stage in the enzymatic breakdown of protein.

indispensable amino acids (essential amino acids)

nine amino acids that must be obtained from the diet because the body does not make adequate amounts to support body needs.

amylase

breaks down carbohydrates

amino acids

nitrogen-bearing compounds that form the structural units of protein. when digested, the various food proteins yield their constituent amino acids, which are then available for use by the cells to synthesize specific tissue proteins

small intestine

protein digestion is completed in the alkaline medium of the small intestines. enzymes from secretions of both the pancreas and intestine take part

hydrochloric acid

provides the acid medium necessary to convert pepsinogen to active pepsin, the gastric enzyme specific to proteins. begins the unfolding and denaturing of the complex protein chains

grains and peas, bean or lentils

brown rice and beans, whole-grain bread with pea or lentil soup, wheat or corn tortilla with beans, peanut butter on whole wheat bread, indian dishes of rice and dal (a legume), chinese dishes of tofu and rice

a state of nitrogen balance may occur during periods of

c. injury or surgery

health benefits and risk

-lower levels of dietary saturated fat and cholesterol from animal products -higher levels of carbohydrates, fiber, magnesium, boron, folate, carotenoids, phytochemicals, and antioxidants such as vitamin c and e -lower body mass index and prevalence of obesity -lower rates of death from cardiovascular disease, including ischemic heart disease, high blood cholesterol, and hypertension -lower risk of type 2 diabetes and some forms of cancer 9prostate and colon) -lowered risk of renal disease from high glomerular filtration rates -lowered risk of dementia

excess dietary intake

1. they are often high in saturated fats, a known risk for cardiovascular disease 2. if a person fills up on protein foods, little room is left for fruits, vegetables, and other whole grains packed with essential vitamins, minerals and fiber 3. the kidneys have the extra burden of getting rid of excess nitrogen.

influential factors of protein needs

1. tissue growth 2. quality of the dietary protein 3. additional needs resulting from illness and disease

lacto-ovo vegetarian diet pyramid

2 servings-fats 2 servings-fruits 4 servings-vegetables 5 servings-legumes, nuts, and other protein rich foods 6 servings-grains

because they are smaller, infants and young children need less proteins per unit of body weight than do adults

FALSE

complete proteins of high biologic value are found in whole grains, dried beans and peas, and nuts

FALSE

protein provides a main source of body heat and muscle energy

FALSE

the average american diet contains a relatively small amount of protein

FALSE

high protein diet

a high protein diet generally are higher in total fat, saturated fat, and cholesterol. initial weight loss associated with a high protein, high fat diet is caused by the induction of metabolic ketosis and fluid loss from a lack of carbohydrates. ketosis eventually suppresses the appetite, ultimately leading to reduced caloric intake and weight loss.

nine of the 20 amino acids are indispensable, meaning that

a. the body cannon make them and must obtain them from the diet

enzymes in stomach to break down protein

all enzymes involved in protein digestion (proteases) are stored as inactive proenzymes called zymogens. zymogens are then activated upon need

intestinal secretions

aminopeptidase and dipeptidase are protein splitting enzymes to complete the breakdown and free the remaining amino acids. produced by glands int he intestinal wall

carboxypeptidase

attacks the acid (carboxyl) end of the peptide chains, producing small peptides and some free amino acids. carboxypeptidase also is first released as the inactive proenzyme procarboxypeptidase and is activated by trypsin.

aminopeptidase

attacks the nitrogen-containing (amino) end of the peptide chain and releases amino acids one at a time, producing peptides and free amino acids

biological value (BV)

based on nitrogen balance

net protein utilization (NPU)

based on the biological value and the degree of the food proteins digestibility

a complete protein food of high biologic value contains

d. all nine of the indispensable amino acids in correct proportions to meet human requirements

chemical score (CS)

derived from the amino acid pattern of the food. a high quality protein food, such as an egg (with a value of 100) is compared with other foods according to their amino acid ratios

legumes and seeds

falafel, soybeans and pumpkin or sesame seeds, middle eastern hummus (garbanzo beans and sesame seeds) or tahini

pepsin

first produces as an inactive proenzyme, pepsinogen, by a single layer of chief cells in the stomach wall. the hydrochloric acid within gastric juices then changes pepsinogen to the active enzyme pepsin. pepsin begins splitting the links between the proteins amino acids, which changes the large protein into smaller short chains called polypeptides. if the protein were held in the stomach longer, pepsin could continue this breakdown until only the individual amino acids of the protein remained. the normal gastric emptying time, pepsin only completes the first stage of breakdown

dispensable amino acids (non-essential amino acids)

five amino acids that the body can synthesize from other amino acids supplied through the diet and thus do not have to be consumed on a daily basis.

protein energy malnutrition (PEM)

kwashiorkor (protein deficiency) marasmus (caloric deficiency)

trypsin

secreted first as inactive trypsinogen, is activated by the enzyme enterokinase. enterokinase is secreted from the intestinal cells on contract with food entering the duodenum, the fist section of the small intestine. the active trypsin then works on proteins and large polypeptides fragments carried from the stomach. the enzymatic action produces small polypeptides and dipeptides.

chymotrypsin

secreted first as the inactive chymotrypsinogen, is activated by the trypsin already present. the active enzyme then continues the same protein-splitting action of typsin

conditionally indispensable amino acid (conditionally essential amino acid)

six amino acids that normally are considered dispensable amino acid because the body can make them. however, under certain circumstances such as illness, the body cannot make them in high enough quantities and they become indispensable in the diet

functions of protein

structural tissue building source of energy (4kcal/g) water balance through osmotic pressure digestion and metabolism through enzymatic action cell signaling (insulin) and transport (hemoglobin and transferrin) immunity (antibodies)

dipeptidase

the final enzyme in the protein splitting system, completes the large task by breaking the remaining dipeptides into two free amino acids.

rennin

the gastric enzyme only present in infancy and childhood and is especially important in the infants digestion of milk. rennin and calcium act on the casein of milk to produce a curd. by coagulating milk into a more solid curd, rennin prevents the food from passing too rapidly from the infants stomach to the small intestine

mouth

the mechanical breaking down of protein foods occurs by chewing in the mouth. the food particles are mixed with saliva and passed on to the stomach as a semisolid mass

ovo-vegetarians

the only animal foods included in the ovo-vegetarian diet are eggs. because eggs are an excellent source of complete proteins, individuals following this diet do not have to be overly concerned with complementary proteins on a daily basis

lacto-vegetarian

these vegetarians accept only dairy products from animal sources to complement their basic diet of plant food. the use of milk and milk products (cheese) with a varied mixed diet of whole or enriched grains, legumes, nuts, seeds, fruits, and vegetables in sufficient quantities to meet energy needs provide a balanced diet

pancreatic secretions

trypsin, chymotrypsin and carboxypeptidase are enzymes produced by the pancreas continue breaking down proteins into simpler and simpler substances

vegans

vegans follow a strict vegetarian diet and consume no animal foods. their food pattern consist entirely of plant foods. (whole or enriched grains, legumes, nuts, seeds, fruits, and vegetables) the use of soybeans, soy milk, soybean curd (tofu), and processed soy protein products enhances the nutritional value of the diet, and these products are well tolerated and accept. careful planning and sufficient food intake ensure adequate nutrition

lacto-ovo-vegetarian

vegetarians who follow a food pattern that allow dairy products and eggs. their mixed diet of plant and animal food sources, excluding only meat and fish, poses no nutritional concerns

grains and dairy

whole wheat pasta and cheese, yogart and a multigrain muffin, cereal and milk, cheese sandwich with whole grain bread