From the results of few studies which have been done, experience with my own gains and from working with others from varied levels of bodybuilding, I feel that protein quality and regularity is more important, than actual amount of protein in grams eaten per day. By consuming quality protein, in respect of what is actually absorbed, a high protein diet will, in fact, be achieved.
Biological value (BV) of protein is a method of assessing how similar a protein source is, in respect of amino acid profile, to that of human requirements. Proteins are grouped into those of high BV (HBV), generally foods of animal origin and some pulses, and low BV (LBV), like cereal-based foods which we eat more for carbohydrate but do contain some protein. It could be argued that bodybuilders need to consume plenty of HBV protein foods regularly, but there are other important considerations.
Amino acids are the simplest units of protein, and are needed in a specific ratio for optimal muscle growth. Even if one is missing the quality of the amount of protein ingested is reduced, so you actually need more total protein. Some amino acids are considered essential / indispensable, as our bodies cannot synthesise them, therefore we must consume them. There are also conditionally essential amino acids, which under certain circumstances we are unable to make enough, for example during physical stress like trauma or bodybuilding. The remaining amino acids are considered non-essential, though what we obtain from our diet are still used abundantly in the body, and they are still crucial to muscle growth.
How akin the amino acid profile is to human muscle tissue, is one issue, as this is the primary reason why we consume so much protein. Another consideration is how readily a particular protein food is digested and absorbed by the body, then taken up by muscle tissue. In this respect there are sources of protein which are better than others, for example whole eggs, whey and red meat. Other proteins are still have their place, but these are best.
"...protein quality and regularity is more important, than actual amount of protein in grams."
Whey protein is one of the main milk proteins, but is not as abundant in milk as casein. Whey protein can be isolated by a variety of processes, the most efficient being ionexchange filtration, which filters out everything, leaving almost 100 % pure whey protein powder available as a supplement. Not only is the amino acid profile of whey very similar to human muscle tissue, but it is also absorbed very quickly as it is semi-elemental, i.e. partially digested. Amino acids are one of the end products of protein digestion, and much protein is absorbed in this form. Peptides are small chains of a few amino acids from partial digestion, and protein is also absorbed in this form, but by a different mechanism to that which absorbs amino acids. A semi-elemental protein source therefore, such as ionexchange whey, containing amino acids and peptides has optimal absorption, as they are absorbed to two separate methods.
Another, more modern, method for evaluating protein quality is something known as the Protein Digestibility-Corrected Amino Acid Scoring (PDCAAS). This is actually a highly accurate method, although the quality score of proteins measured this way does differ to that of the BV scoring system. PDCAAS takes into account the profile of essential amino acids of the protein in question, as well as its digestibility in humans, rather than in rats. It is the method of assessing protein quality adopted by the World Health Organisation / Food and Agriculture Organisation (WHO/FAO) and the US Food and Drug Administration (FDA).
With PDCAAS, the proteins with a high BV score also rank quite high, but it also ranks isolated soy protein as one of the highest (WHO/FAO 1989), and casein scores higher than whey. Note that it is only isolated soy protein that has the high score, soy protein concentrate (which is used in many poor quality protein powders) does not. Isolated soy protein has also been shown to help boost thyroid hormone levels during calorie-restricted diets, a time when thyroid hormones decline (Barth, et al 1989; Forsythe 1995), thus boosting metabolic rate. A recent study showed isolated soy protein produced antioxidant beneficial effects in athletes who used it, compared with athletes who used whey protein (DiSilvestro 2000).
Confused? I am! Well, this is just one example of many inconsistencies in the science of nutrition. It is another inconclusive fact that dietitians and nutritionists, such as myself, have to convert into relevant information for the public to make use of.
One problem with PDCAAS in respect to bodybuilding nutrition, is the high requirements of all amino acids, not just the essential ones, and this is a downfall of isolated soy protein.
From this, you can conclude that all the proteins that score high from the BV score are of good quality, as is isolated soy protein. The best way to ensure maximum protein quality is by mixing protein sources with each serving. For example, rather than having 200g tuna at one meal, and a chicken breast at the next, try having 100g tuna and half a chicken breast at both meals. This will give a wider spectrum of amino acids, so will be more in line with that of muscle tissue. Although soya and protein from other pulses is of lower quality that animal sources, in this way you can include them in your diet, hence reap their additional health benefits, e.g. have fish and baked beans at a meal.
In some circumstances, e.g. when eating out, it may be inconvenient to mix proteins, in which case supplement the meal with five or six amino acid capsules, thereby improving the amino acid profile available to the body.
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