Individual amino acid requirements

It is hard to define amino acid requirements because various estimates have been proposed. When determining requirements for individual circumstances, test reliability and the body’s adaptive abilities must be considered. When looking at requirements, understand that there is probably a difference in requirements for people concerned with maintenance issues versus individuals looking to enhance performance, strength, or hypertrophy.

To determine whether an amino acid is indispensable, it is omitted from the diet while all the other amino acids are included. If the omission results in a negative nitrogen balance, the amino acid is considered indispensable. In the absence of this single amino acid, the body has been unable to synthesize certain proteins so that the nitrogen that would have been used in the synthesis is excreted. By this criterion, the amino acids isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine are indispensable in humans.

However, not all of the other amino acids can be considered dispensable at all times. Under certain circumstances, certain dispensable amino acids may become rate limiting for protein synthesis. These amino acids become conditionally essential (indispensable). For example, histidine is known to be required for normal growth in a child. Proline and glutamine are other amino acids that may be conditionally essential (they may be needed in higher levels during lactation because of their unique contributions to milk protein synthesis). Phenylalanine and methionine are indispensable amino acids. If they are available in the diet at or below minimal requirement levels, tyrosine and cysteine can become indispensable amino acids because the lack of precursor amino acids decreases the body’s ability to produce these amino acids. They then become rate limiting for protein synthesis.

Below is a chart giving indispensable amino acids requirements from the 1985 FAO/WHO/UNU. The recommendations are given for four age groups. These values indicate that the requirements per unit of body weight decline substantially between infancy and adulthood with the requirement for the total of the (IAA) falling from 714 mg· kg·d in 3–4 month old infants to 84 mg·kg·d in the adult. When expressed per unit of safe protein intake (less histidine), the pattern of change with growth development is also marked in that there is a fall in the total IAA to protein ratio with the value for infants being 434 mg·g protein compared with adults in whom the comparative value is 111 mg·g protein (chart is given in Protein Essentials).

What matters to athletes is how to get a sufficient quantity of indispensable amino acids. If protein intake is sufficient, there should not be a problem getting the amount needed. High quality protein foods have a sufficient quantity of IAA to support needs. In fact, if you are consuming the amount of protein suggested earlier in the book, you are probably getting more IAA than you can utilize. It is often suggested that one protein is superior to another in terms of quality due to a higher content of a particular amino acid. In reality, this matters very little if the quantity of the amino acid (in the protein with the lower amino acid content) is sufficient to meet needs. Once needs are met going higher is not necessarily better.

The values given in the tables above weren’t designated for athletes. Recent studies have validated the need for higher protein intake (meaning higher amino acid intake) in strength and endurance athletes. Studies have also indicated that particular amino acids may be needed in higher quantities under certain circumstances (mentioned earlier). One example would be during exercise and dieting (particularly BCAAS and glutamine). In reality, eating a sufficient quantity of high quality proteins will probably cover the body’s needs. Is one protein better than another? Assuming that sufficient quality and quantities are being ingested, there is probably little difference in the benefits.

thanks,
Coach Hale
www.maxcondition.com