Transcript Chapter 4
Judith E. Brown www.cengage.com/nutrition/brown Proteins and Amino Acids Unit 15 Prof. Albia Dugger • Miami-Dade College Protein • Protein is an essential component of all living matter, and is involved in almost every biological process in the body • Protein • Chemical substance in foods • Made up of chains of amino acids Protein’s Image • Most people in the US get more than enough protein in their diets • High protein diets are usually high in fat and low in fiber Fat Content of “Lean” Meats Functions of Protein Functions of Proteins cont. • A 154-pound man contains about 24 pounds of protein – about half in muscle • Also in skin, heart, liver, intestines, other organs, blood, enzymes, and immunoproteins • All proteins in the body are continually broken down and rebuilt Functions of Proteins cont. • Red blood cells and fibrin (which helps blood clot) are made primarily from protein Proteins as an Energy Source • Protein can serve as an energy source • 4 calories/gram • Not a primary energy source • Does not have a storage form in the body • For proteins to be used as energy, nitrogen must be removed from amino acids • Excess nitrogen is excreted in urine Amino Acids • Proteins are made of amino acids that have been linked into chains • • • • • 20 common amino acids Order of amino acids is determined by DNA Chains can have >2,500 amino acids Chains fold into complex shapes Order and shape determine protein function Key Terms • DNA (deoxyribonucleic acid) • Genetic material contained in cells that initiates and directs protein production in the body Key Terms • Essential (indispensable) amino acids • Cannot be synthesized in adequate amounts by humans – must be obtained from the diet • Nonessential (dispensable) amino acids • Can be readily produced by humans from components of the diet Amino Acids Forming Proteins Proteins Differ in Quality • High quality protein contains all essential amino acids in the amounts needed for protein tissue formation • If one amino acid is missing, all proteinproduction shuts down • We need to consume sufficient amounts of all essential amino acids every day Complete Proteins • Complete proteins • Contain all of the essential amino acids in amounts needed to support growth and tissue maintenance • Found in animal products such as meat, milk, and eggs Incomplete Proteins • Incomplete proteins • Proteins that are deficient in one or more essential amino acids • Proteins in plants are incomplete • “Complementary” plants sources can be combined to form a “complete” source of protein Complementary Plant Food Combinations Vegetarian Diets • Vegetarian diets consisting only of plant foods can provide an adequate amount of complete proteins • A variety of complementary protein sources must be eaten each day Amino Acid Supplements • High intakes of individual amino acids can disrupt normal protein production • Example: methionine • • • • Worsens symptoms of schizophrenia Promotes hardening of arteries Impairs fetal and infant development Causes nausea, vomiting Amino Acid Supplements • Adverse effects have been reported with several amino acid supplements Supplements and Muscle Mass • Athletes take amino acid supplements to increase muscle mass and strength • The real key is resistance training followed by high-quality protein foods Food as a Source of Protein • In US, average protein intake exceeds RDAs • 70% of protein comes from animal products • Plant sources of protein are lower in fat • Dried beans, grains • Most food sources of protein also provide vitamins and minerals Food Sources of Proteins Protein Plus • Beef and pork are also good sources of iron Too Little Protein • Protein deficiency can occur by itself, or with a deficiency of calories and nutrients • Iron, zinc, vitamin B12, niacin • Body protein is used as an energy source during starvation • Reduces strength, lowers immunity, causes abnormal organ functions and death Key Terms • Kwashiorkor • A form of severe protein-energy malnutrition in young children (associated with starvation) • Characterized by swelling, fatty liver, profound apathy, susceptibility to infection, poor appetite • Not corrected by improving protein intake Too Much Protein • Consumption of 45% of total calories from protein is considered too high • Causes nausea, weakness, diarrhea • High-protein diets • Result in weak bones, kidney stones, cancer, heart disease, obesity • Very high-protein diets • Such as “rabbit fever,” may cause death