Proteins Chapter 5
Nov 02, 2014
Proteins
Chapter 5
What are proteins?
• Amino acids linked together
• Composed of:
– Carbon
– Hydrogen
– Oxygen
– Nitrogen
Protein Structure
• Peptide bonds
• Structure– Primary– Secondary– Tertiary
Amino Acids
• 20 amino acids• 9 essential amino
acids– Come from diet
• 11 nonessential amino acids
• Conditionally essential amino acids– Tyrosine– Cysteine
Protein Classification
• Number of amino acids– Dipeptide– Tripeptide– Oligopeptide
• Composition– Complete– Incomplete
• Quality– High– Low
High-Quality Protein
• A complete protein
• Contains extra amino acids for protein synthesis
• Good digestibility
• Usually from animal-derived foods
Photo © Mark Adams/Superstock
Low-Quality Protein
• An incomplete protein
• One or more limiting amino acids
• Usually from plant-derived foods
Photos courtesy of the USDA
Complementing Proteins
• Complementing proteins are incomplete proteins that when eaten together provide a full complement of all essential amino acids.
Photo © PhotoDisc
Complementary Protein Combinations
Food examples:•Beans & rice•Peanut butter sandwich on whole grain bread•Lentil soup with whole grain bread
Protein Functions
• Tissue building – builds muscle
• Cell functioning– Enzymes
• Body functioning– Hormones– Immune function– Fluid balance
• Energy source
What is nitrogen balance?
Nitrogen balance is an indicator of nitrogen status and thus protein intake.
Equals: (Nitrogen in) – (Nitrogen out)
How much protein is needed?
Factors Influencing Protein Requirements
• Total energy intake
• Desire to lose or gain weight
• Carbohydrate availability
• Exercise intensity and duration
• Training status/fitness level
• Dietary protein quality
• Age
Protein Sources
Questions to Ask About Protein Supplements
•What is the quantity of protein or amino acids in the product?
•Is the supplement necessary?
•What is the cost?
•Will it enhance performance?
•Does the supplement have any harmful effects?
What should an athlete eat in the hours leading up to competition or training?
• 4 to 24 hours prior to exercise:– Balanced high-
CHO meals/snacks – Familiar foods– CHOs, not proteins,
should predominate
Photo © Photodisc
How much protein should be consumed 4 to 24 hours before competition?
• Depends on how much time before exercise is initiated
• Lean protein sources– 3 to 6 oz turkey, fish, soy
or– 8 to12 fl oz dairy
or– Complementing low-fiber plant sources
How much protein should be consumed 1 to 4 hours before competition?
• Focus should be on CHO• Small amounts of protein okay (i.e., 2–4 oz lean
meat)• Lean protein sources preferable
What about protein consumption during competition?
• Protein can serve as an energy source.
• Consumption during exercise is questionable.
• There is some research support for branched chain amino acids during competition.
What about protein consumption after competition?
• 6 to 20 grams of high-quality protein – Casein– Whey– Soy
• Essential amino acids are key.• Should be consumed within 3 hours after
competition.• Hydrolyzed protein sources are absorbed more
quickly.