Proteins

Chapter 5

What are proteins?

• Amino acids linked together

• Composed of:

– Carbon

– Hydrogen

– Oxygen

– Nitrogen

Protein Structure

• Peptide bonds

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

• 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.

• It’s not necessary to eat complementing protein sources together at same meal but at least within same day.

Photo © PhotoDisc

Complementary Protein Combinations

Examples of complementary protein combinations:

Rice and beansPeanut butter on whole wheat bread

Protein Functions• Tissue building: important for athletes trying to put

on muscle mass.

• Cell functioning

– Enzymes

• Body functioning

– Hormones

– Immune function

– Fluid balance

• Energy source: prefer not to use protein as energy source but if athlete isn’t taking in enough calories then protein will be diverted from other important functions to be used for energy.

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.