Using Quality and Timing of Dietary Protein to Your Advantage

Many people are aware that there is more than one kind of carbohydrate or one kind of fat. This is actually very easy to realize if you have ever looked at a food label before. First, with fats you will notice there is a column for “Total Fat” which is then broken down into multiple other columns including: saturated fats, unsaturated fats (which is broken down into monounsaturated and polyunsaturated), and trans fats. With a little research, often from right on the food package, you would quickly realize that you should try to get your dietary recommended intakes (DRIs) of dietary fat from unsaturated fat sources, while keeping saturated fats very low, and trans fats as close to zero as possible. Very simple! Moving on to carbohydrates you will see a similar situation. There is a bolded column for “Total Carbohydrates” which, just like “Total Fat," is broken down into the subcategories fiber (broken down further to soluble and insoluble fiber) and sugars. But what about protein? There is only one category listed on the food label. So protein must be simple to understand, right? Unfortunately it is quite a bit more complicated than that.

Please Note:

This post is advanced and intended more for the fitness professional.   A simplified version is in the works! 

Similar to carbohydrates and fats, there are many different types of proteins that all have different structures and functions. Research on how much protein should be consumed has been investigated relatively deeply. Most research and textbooks agree that exercising athletes should consume somewhere in the range of 1.4-2.0g of protein per kg of bodyweight daily (Campbell et al., 2007; Fink et al. 2009). However, research on which protein is best for various populations and timing of protein ingestion is relatively new and unexplored. Nevertheless, the limited results are showing that the ingestion of specific proteins at certain times may offer significant advantages, especially for the athletic population. Also, the use of protein supplementation has become very widespread and the number of available products is almost endless, making the available proteins to choose from even larger. All together, this leads to two questions that every athlete should ask: What protein should be consumed, and second, at what time should it be consumed?

When determining which proteins to consume, the “quality” must first be considered. The three determinants of a protein’s quality include essential amino acid (EAA) composition, digestibility, and the bioavailability of amino acids.

The first determinant of protein quality, EAA composition, considers the relative proportion of essential amino acids a certain protein contains. EAA are the nine amino acids that cannot by synthesized by the body and must be obtained through diet. If they are not, protein synthesis is impaired and, over time, body protein content decreases (Lemon, 1991) since only EAA are needed to stimulate muscle protein synthesis (Tang et al., 2009). A high quality protein will contain all nine essential amino acids. Proteins are often termed either complete or incomplete, where complete proteins contain all the EAA and incomplete proteins are missing at least one EAA. Most animal proteins are complete while almost all plant proteins are incomplete (soy is an exception). For those consuming only incomplete sources of protein, complementing in the diet is required. Complementing is accomplished by consuming two or more incomplete protein foods that when eaten together provide the full complement of essential amino acids (Campbell et al., 2007). This practice is especially important for vegetarians. Fink et al. (2009) make an important point that although the terms complete and incomplete are often used to categorize protein sources, they should not be inferred to mean "superior" and "inferior." For example, in a study by Tang et al. (2009) on maximizing muscle protein, they noted that animal proteins, which are complete proteins, usually contain high saturated fat and cholesterol. Both of these are considered health risks that are linked heavily to cardiovascular disease.

The second determinant of protein quality, digestibility, is very important to the rating process. Merriam-Webster (2009) defines digestibility as the percentage of a foodstuff taken into the digestive tract that is absorbed into the body. That is, as Hoffman and Falvo (2004) state that "digestibility measures the efficiency of digestion" and therefore allows the consumer to calculate the percent of the total ingested protein that can be utilized.

The third determinant of protein quality is the bioavailability of amino acids. Bioavailability is the degree and rate at which a substance is absorbed into a living system or is made available at the site of physiological activity (Merriam-Webster, 2009). The higher the bioavailability of a protein source, the greater the total absorption and rate of absorption that will occur. When referring to quality of protein, a high quality protein will have a high bioavailability.

To measure these three characteristics (primarily the digestibility and bioavailability) and give proteins a quality rating, five methods can be used. The inferior methods for measuring protein quality that are occasionally used include the Chemical Score, Net Protein Utilization (NPU), and Protein Efficiency Ratio (PER). These methods are considered inferior due to the fact that they do not consider the digestibility and absorption of protein. Therefore the last two methods, Biological Value (BV) and Protein Digestibility Corrected Amino Acid Score (PDCAAS), are the superior testing methods, with PDCAAS being the gold standard, and both measure the digestibility and absorption.

Biological Value is commonly used when advertising foods and especially protein supplements. The BV is considered superior because it measures how much of the consumed protein that actually enters the bloodstream (i.e. digested) is retained in the body (i.e. absorbed). Unfortunately, there are two scales used for scoring BV which can often lead to confusion. The first scale measures the actual percentage of digested proteins that are retained in the body, while the second method measures the same percentage relative to another high quality protein, often an egg. Therefore, the first method can be termed an absolute measure of BV, and the second a relative measure of BV. Using the absolute measure of BV, the maximum score would be 100% where higher scores designate a higher quality protein. A protein that has a BV of 100%, indicates that all of the protein digested was utilized by the body. Whey protein scores a 100%, eggs (~93%), fish (83%), beef (80%), and chicken (79%) (Mase, 2009) when using the absolute measure of BV. When using the relative measure of BV, the protein being measured for quality is compared to a reference protein, which is most often the egg. Since eggs have an absolute protein BV of about 93%, a score of greater than 100% is possible, as is the case for whey protein isolate and concentrate, which score relative BVs of 159% and 104% respectively (Hoffman and Falvo, 2004). Because of the slight variations in the two BV measuring methods, someone who is considering purchasing a protein supplement should be aware of what method was used to rate the BVs of various products.

The "gold standard" PDCAAS was adopted by the FDA in 1993 and is the newest method of scoring protein quality. PDCAAS is the method most frequently used in professional resources. Using the PDCAAS method, the protein quality ranking are determined by comparing the amino acid profile of a specific protein against a standard amino acid profile. The key factor in making the PDCAAS method the gold standard is that it allows evaluation of food protein quality based on the needs of humans as it measures the quality of protein based on the amino acid requirements, adjusted for digestibility of a 2- to 5- year old child since they are considered the most nutritionally-demanding age group (Hoffman and Falvo, 2004). The highest score possible is a 1.0, which indicates that after digestion of the protein, it provides 100% or more of the indispensible amino acids required. Proteins can have a score over 1.0, but in 1990 at a WHO meeting it was decided that proteins having values higher than 1.0 would be rounded down to 1.0. Hoffman and Falvo (2004) shared the PDCAAS values of proteins of high interest including , in descending order, whey (1.0), eggs (1.0), casein (1.0), milk (1.0), soy (1.0), beef (0.92), vegetables (0.74), legumes (0.69), whole wheat (0.54), lentils (0.52) and wheat gluten (0.25).

Moving away from protein quality and onto protein timing, a study by Boirie et al. (1997) begins to show just how important timing of protein can be. Their study was aimed to better understand how the speed of absorption of dietary amino acids by the gut varies according to the type of ingested dietary protein. To test this they studied the effect of two milk proteins, whey and casein, on postprandial whole-body protein metabolism. They hypothesized that the speed of absorption by the gut might affect whole body protein synthesis, breakdown, and oxidation, which in turn control protein deposition. Their results showed findings of significant importance.

The subjects who consumed the whey protein were reported to have a "high, rapid, and transient peak" in plasma amino-acid levels. This peak was associated with a pronounced increase in protein synthesis, but no change in protein breakdown. By contrast, the plasma appearance of dietary amino acids after the casein meal was slower and lower, but much more prolonged with a different whole body metabolic response where protein synthesis increased slightly, but protein breakdown was significantly inhibited. In fact, the subjects who consumed casein protein maintained amino acid concentrations above baseline beyond the 7-hour trial.

Taking all this information on the quality of protein, an athlete can begin to answer the questions asked initially; "What kind of protein should be consumed, and when should it be consumed?"

First of all, in any diet, variation is very important. Variation lowers the risk of not obtaining, or dangerously exceeding, DRIs of nutrients. Athletes should however focus on complete proteins with the highest quality ratings. Egg whites, fish, chicken breasts, and lean beef are all great "whole food" sources of high-quality, complete proteins that have high digestibilities and lower saturated fats and cholesterol. These should be staple items of athletes' normal, everyday diets. The very high quality ratings of protein supplements, especially whey, make supplementation very appealing. However, protein supplements, should be used as just their name implies, as a supplement to a normal diet. Arguably, protein supplements seem to be most beneficial when considering timing of protein ingestion.

As for timing, similar to certain carbohydrates being recommended at particular times, protein timing should also be considered, especially by athletes. As mentioned above, research shows the possibly enhanced benefits of consuming certain proteins, especially whey and casein supplements, at certain times (Boirie et al., 1997). To begin with, consider when you sleep. While sleeping, you are not able to eat, and therefore the nitrogen balance will move in a negative direction, which could mean either the breakdown of body tissues (muscle), the inhibition of body tissue growth, or both. If you are only in a negative nitrogen balance for say three hours while sleeping, it is easy to consider that amount of time insignificant. However, consider the amount of potential loss in body tissue that could be incurred over a long period of time from only three hours of negative nitrogen balance per night. In one year that is 1,095 hours or 45.63 days worth of tissue breakdown. After 5 years: 5,475 hours or 228.13 days. And after 10 years: 10,950 hours or 456.25 days. This all of a sudden becomes exceedingly significant to an athlete wishing to improve performance and maximize growth. To minimize the amount of time in negative nitrogen balance while sleeping, consuming 30g of casein protein before sleeping could at least prevent the breakdown of tissue due to the very prolonged rise in blood amino acid levels it provides (Boirie et al., 1997).

In the morning, physiologically and biochemically, it would make sense to consume a protein that provides a quick digesting protein to "break the fast" that occurs during the sleep. Whey protein would appear to be the best choice in this situation since it is digested and absorbed very rapidly. Once again the importance here is to limit the amount of time the body is breaking down tissue, and rather building or, at minimum, maintaining.

Finally, when planning meals around workouts, a combination of both whey and casein protein, or even smaller but more frequent ingestion of whey protein may be most beneficial (Hoffman and Falvo, 2004) when looking to maximize results in athletic performance measures. Casein has been shown to provide the greatest benefit for increases in protein synthesis for prolonged duration, while whey protein has a greater initial benefit for protein synthesis. Studies attempting to determine, which protein is best before and after workout often have conflicting viewpoints, and so the safest method for an athlete wishing to maximize improvements in athletic performance may be to consume a combination of whey and casein before, during, and after exercise.

Hopefully it is evident by now that protein quality and the timing of protein ingestion should be important aspects of any athlete's nutritional plan. When deciding on what protein to consume and at what time to consume it, an athlete can easily become confused due to the often unrealized complexity of proteins. With this, it is critical that coaches, athletic trainers, and nutritionists provide guidance and education for their athletes when it comes to dietary protein. Further studies into this area of research are much needed and would appear to be very appropriate.