Part 3 of Dr. Wagners's series on Protein
by Dr. Rob Wagner
In the last two segments of this post I provided some information on the amount of protein a human can process from a meal. This was based on the concept that we can’t use more than 30 grams of protein, or digest more than 30 gram from a meal. In this final installment I will discuss the effects of the quality and different types of protein on the body and how other nutrients affect protein absorption. I will also provide insight to research on protein and athletes and give you a guideline to follow for protein ingestion.
Quality of protein (nutritional value)
To be effective dietary protein must have all the Essential amino acids. There are nine that the body cannot make or make in sufficient amounts. These must be included in the diet and they are Histine (less important as we age), Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Trytophan, and Valine. Conditionally Essential AA are the six that are important but made by body Arginine, Cystine, Glutamine, Glycine, Proline, Tyrosine. The final five are Non-essential because they are less important and made or converted in body, Alanine, Asparagine, Aspartic Acid, Glutamic Acid, and Serine. Complete proteins have the 9 essential amino acids and are only found in animal protein and soy protein. I know that people say Quiinoa (a grain) is also complete but I can’t verify this. Typically all plant sources w/ the exception of soy are incomplete because they lack one or more of the essentials. High quality proteins contain all the essentials in their proper proportions. I will let you look those proportions up to due space limitations here.
The bioavailability of ingested AA and their Nitrogen is their efficiency in their metabolic utilization. Low quality protein and the incompletes have been shown to increase urea production because they increase the flow of AA going to the Liver. The AA from these sources are not as coveted by the gut (remember that?) and are passed along to the liver for energy usage. The intake of these low quality proteins contributes to lower net protein synthesis. High Quality proteins increase AA usage in the gut which induces AA retention hence they don’t travel to the liver and they can be used for structural purposes which has the opposite effect.
Other nutrients also seem to play roles in the absorption of AA. Fats typically are found to slow the transit time of protein through the digestive system and hence slow the rates at which it is digested. Carbohydrates have probably been studied more than any other nutrient in combination with protein. These studies have looked at the effects of both when taken in combination on AA absorption, insulin release, glycogen replenishment, BCAA function and on and on. Here is the Readers digest version. Carbs when ingested with Protein can dampen the effect of using AA for energy and there is also a greater retention of AA in the gut. This means when carbs and protein are ingested together you positively affect nitrogen balance. Fiber has an interesting role. When research looks at fecal nitrogen (excreted nitrogen) it tends to increase when protein is ingested with fiber. However, the N balance is rarely affected. The belief is that the increase in excreted N is related to the increase in bacterial activity in relation to the presence of fiber in the large intestine.
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Slow vs. Fast
Slow vs. Fast
What makes a fast vs. slow protein? Well it goes back to the rates of absorption I had mentioned in the 2nd installment. Whey protein is a great example of a fast protein. First, it’s soluble (it mixes with water). Anyone in their forties can appreciate a protein that mixes in water, remember the good old days with egg and other protein mixes that globbed up and floated on the top of whatever liquid you were mixing it with. Liquid protein is easier to digest, the enzymes have easier access to it and they break it down much faster due to this. Also, when you add whey isolates you are looking at smaller peptide chains of protein that are easier to break down. Based on the research whey has an absorption rate of about 8-10g/hour. Rates lower than this would be considered slow proteins. Most slows are not liquid and if they are (milk) they coagulate in the stomach (making them into solids like cottage cheese) which again slows the ability of the enzyme action.
Both types of protein have their pros and cons. Fast proteins are considered to have a positive effect on protein synthesis in response to its ingestion (after activity). Slow proteins actually help reduce protein breakdown and this lasts for up to 7 hours after ingestion (Slow protein before bed). This effect also helps maintain protein balance. On the downside fast proteins stimulates AA breakdown. Because they breakdown and release AA faster, these AA enter the liver faster and get used for energy instead of structure. The downside on slow protein is the time it takes to get into the system. Slow protein in the am will give you a steady supply but won’t give you the initial protein feeding your body needs after sleeping (fasting) 7-8 hours. If we consider these numbers they also give some insight into the optimal amounts of protein. Protein absorption at 6-7g/hr. provides the best protein balance. In a 24 hour period this amount would equal 144 -168g/protein/day for an 80k (176lbs. person). These numbers are far lower than the 301-365 gr from the high end intakes discussed in the last installment. Plus those higher protein amounts would require an absorption rate of 12.5 -15 g/h and we know this is not an optimal rate range for protein balance.
Exercise data
The effects exercise has on the body and its need for protein is actually quite interesting. Common sense would have one think that when you increase activity you increase caloric needs so you should increase protein. However, the human body works to preserve itself. It is always focused on maintaining homeostasis. This is the one part of our genetics that has allowed to evolve into a top of the food chain organism. Before I delve into this let’s first look at the ACSM guidelines for protein intake in athletes. Endurance athletes are recommended to take in 1.2-1.4 g/kg-1 (.54 - .63g/lbs.) of bodyweight per day. Strength athletes need 1.2-1.8 g/kg-1 (.54 - .82g/lbs.) of bodyweight/day. These numbers seem quite low when compared to the protein recommendations from the muscle mags and training gurus. But there’s the rub. The ACSM guidelines are based unbiased research and this research is not driven by supplement company research subsidies or an individual that has something to sell.
Now back to our body. I mentioned that the body’s goal is preservation. Some examples of this are the clotting of our blood when we are cut and the healing of bones when they break. But how about our metabolic systems, how are they affected by changes in diet and activity? We know that when we move to a colder environment our body increases its metabolic machinery most likely to maintain body temp. The appetite will adjust to keep pace with this new demand (again survival). The same happens with sedentary folks that start to exercise, if the diet isn’t controlled they tend to gain or maintain their weight due to the increase in appetite in response to the increase in energy usage, not from the exercise bout but from the 5-10% increase in energy usage in response to the workout. So here is some evidence from protein and exercise specifically: Protein turnover becomes more efficient with endurance training when energy balance is maintained (same caloric levels). The body’s demands for repair might override using protein as an energy source. If the calorie needs are being met, than AA will not be used for energy. This is a response to the training itself. The same occurs for strength athletes as well. There is the evidence of better protein turnover efficiency in response to training. In some situations protein needs have been shown to get lower as a response to a consistent training program. Response to protein ingestion has also been shown to be consistent regardless of delivery of Protein (whole food vs. supplements) in relation to resistance training. I can recall reading studies, in preparation for my doctoral comps, which showed that muscle cells will hypertrophy in response to resistance training regardless of post workout nutrition. The idea here is that the body is making better use of the available protein.
Resistance exercise has been shown to reduce protein breakdown and protein synthesis, while at the same time it has been shown to increase net protein balance. This means novices’ requirements after training would be lower, not higher. Other studies have shown that untrained subjects burn more protein when on High Protein diets while others have shown habitual high protein elevates protein needs. Don’t get me wrong I would be a hypocrite if I didn’t tell you I went down the high protein-low carb path and found it very effective for weight control and loss, but in hind sight I was burning a lot of expensive AA for energy. In the body’s increased protein efficiency in response to exercise there seems to be one AA that plays a big role. Leucine is one of the essential AA and is also a Branched Chain AA (BCAA). It has been found to play more roles in maintaining muscle tissue integrity than the other amino acids. Leucine ingestion increases muscle protein synthesis after exercise. Research has also shown increases in muscle hypertrophy in energy deficient diets when Leucine is ample. Check out Ori Hofmeckler’s writings for more information.
While the typical logic would be to increase protein in response to training, the research has shown that this logic may be flawed. It seems the body becomes more efficient at using the available protein sources when individuals are also training. Activity also seems to play a role in regulating things like protein synthesis and hypertrophy making them independent from dietary protein intake. So this brings me to the point. When you look at the high protein quantities typically suggested they don’t match the research. Recall quickly the 6-7g per hour concept of maintaining N balance. Remember this would give us a range of 144 gram – 168g/day for an 80kg person. If you look at the ACSM guidelines for strength athletes they would be 95g/day – 144g/day for that same 80kg person. Interesting overlap isn’t it? The lower end numbers provided by the ACSM meet the guidelines for optimal Nitrogen balance presented. The high end of those Nitrogen balance numbers would still be less than 1g/lbs. and would come in at .95/lbs. BW.
In summarizing this three part post, there is still one standing question. Can your body handle more than 30 grams of protein in a meal? I think based on the info I presented the answer is a resounding yes. However, there are some important points to review. The rate at which proteins are absorbed is based on the protein type, protein quality, protein source, the status of the intestinal needs for AA, what other foods/nutrients are being eaten in addition to the protein, the type of training you do and how long you have been training. All of these play a role in these rates. In one respect the idea of absorbing 30 grams in an hour may in fact have some merit since we can see that most foods don’t enter the system this quickly and according to our Nitrogen balance approach you wouldn’t want them to. So the next time you’re dining and after eating a 12 oz. T bone with 84 g of protein and your dining partner says “you know you can’t absorb more than 30 grams of protein from a meal.” Tell him he’s right, smile in satisfaction and enjoy knowing you are about to start an 8-10 hour infusion of quality AA.
