Protein Requirements and Sources
Currently, the US Recommended Daily Allowance (RDA) for protein in healthy adults is 0.8 g/kg (0.36 g/lb) of body weight per day. Unfortunately, this does not take into account exercise, which adds several levels of complexity. Some factors that need to be considered include protein quality, energy intake, carbohydrate intake, mode and intensity of exercise, and the timing of the protein intake. The RDA for protein is estimated to be sufficient to meet the need of most (97.5%) of healthy men and women age 19 years and older.
For exercising individuals, this may not be enough protein to offset the oxidation of protein/amino acids, which is approximately 1-5% of the total energy cost of exercise, nor is it sufficient for lean muscle growth or for the repair of exercise induced muscle damage.
Protein recommendations are based on nitrogen balance assessment and amino acid tracer studies. Insufficient amounts of protein in exercising individuals may cause a negative nitrogen balance, which will lead to increased catabolism (muscle breakdown) and impaired recovery from exercise.
For endurance exercise, recommended protein intakes range from 1.0 to 1.6 g/kg (0.45 to 0.73 g/lb) per day depending on the intensity and duration of the exercise and the training status of the individual. For example, elite endurance athletes require protein intakes towards the upper end of the preceding range. Additionally, as endurance exercise increases in intensity and duration, there is an increased oxidation of branched-chain amino acids, which creates a demand within the body for protein intakes at the upper end of this range.
For strength/power exercise, protein requirements are thought to be even higher, particularly during the initial stages of training and/or sharp increases in volume. Typical recommendations for strength training range from 1.6 to 2.0 g/kg (0.73 to 0.91 g/lb) per day.
Popular media often mistakenly reports that a chronically high protein intake is unhealthy and may result in unnecessary metabolic strain on the kidneys. Another concern that is cited is that high protein diets increase the excretion of calcium thereby increasing the risk for osteoporosis. Both of these concerns are unfounded as there is no substantive evidence that protein intakes in the ranges suggested above will have adverse effects in healthy, exercising individuals.
The majority of scientific evidence cited was generated from animal models and patients with co-existing kidney disease. In a well designed prospective cohort study, it was surmised that high protein intake was not associated with kidney functional decline in women with normally operating kidneys.
As for increasing the risk of osteoporosis, it is now known that the phosphate content of protein foods (and supplements fortified with calcium and phosphorous) negates this effect.
To obtain supplemental dietary protein, exercising individuals often ingest protein powders, which are convenient and can be cost-efficient. Common sources of protein include milk, whey, casein, egg, and soy-based powders. Different protein sources and purification methods may affect the bioavailability of amino acids. The amino acid bioavailability of a protein source is best conceptualized as the amount and variety of amino acids that are digested and absorbed into the bloodstream after a protein is ingested. Consideration of the bioavailability of amino acids into the blood, as well as their delivery to the target tissue(s), is of greatest importance when planning a regimen of pre- and post-exercise protein ingestion.
The quality of a protein source can be determined by the protein digestibility corrected amino acid score (PDCAAS). Milk-derived whey protein isolate has the highest PDCAAS out of all of the common protein sources due to its high content of essential and branched chain amino acids.
Commercially, the two most popular types of proteins in supplemental form are whey and casein. Recent investigations have detailed the serum amino acid responses to ingesting different protein types. Using amino acid tracer methodology, it was demonstrated that why protein elicits a sharp, rapid increase of plasma amino acids following ingestion. Consumption of casein induces a moderate, prolonged increase in plasma amino acids that was sustained over a 7 hour period after eating.
The (International Society of Sport Nutrition) ISSN recommends that exercising individuals consume approximately 1.4 to 2.0 g/kg (0.64 to 0.91 g/lb) of body weight per day. An attempt should be made to obtain protein requirements from whole foods, but supplemental protein is a safe and convenient method of ingesting high quality dietary protein. When supplements are ingested, the ISSN recommends that the protein contain both whey and casein components.
Sphere It125 views
Related posts:
- Soy Protein May Not Be So Bad
- Prevent Diabetes With A Low-Carb Diet
- Weekly Nutrition Tip #14
Did you enjoy this post? Why not leave a comment below and continue the conversation, or subscribe to my feed and get articles like this delivered automatically each day to your feed reader.
Trackbacks & Pingbacks
[...] It appears that soy protein supplementation does not cause an increase in estrogen in men. Personally, I use a more high quality protein source such as whey or casein. This supplies more BCAAs and provides a more conducive diet for muscle growth. For more information on protein requirements check out a previous post here. [...]
Comments
Leave a comment
Line and paragraph breaks automatic, e-mail address never displayed, HTML allowed:
<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>