The free amino acid pool is mainly located inside cells and constitutes only about one percent of the body's total amino acid content in the form of proteins. Since the free amino acid pool is smaller than the daily incoming amount of amino acids from food, the consequence of one day of protein deprivation could be disastrous. Luckily, the body has solved this problem by having a very high rate of protein turnover [more than one pound daily], and by keeping a pool of labile [this means they can easily change] proteins which are readily available to be broken down without interrupting normal body functions.9,14,17 By having this high rate of protein turnover, the body can easily change the distribution of proteins, and this is of prime importance. During infection [a form of metabolic stress], for example, when the body needs to synthesize antibodies [which are proteins], the building blocks [amino acids] will be taken mostly from labile proteins, but unfortunately, during longer periods of sickness, starvation, or trauma, muscle protein will also be broken down to provide raw material for new proteins.
By studying the chart, you can see how I came to the conclusion that there are at least four areas we as bodybuilders must target: 1) decrease amino acid breakdown, 2) increase protein synthesis, 3) decrease protein breakdown, and 4) increase the proportion of newly synthesized muscle proteins. All the details about how to accomplish this are too complicated to get into in this article. However, in regard to protein intake, I can mention that degradation, or breakdown, is temporarily suppressed by an increased protein intake,8,16 and synthesis is promoted at intakes above 1.4 grams of protein per kilogram of bodyweight per day [g/kgBW/d].16,21 For a 200-lb lifter, that's about 130 grams of protein per day.
The size of the free amino acid pool is remarkably constant,24 and this, my friends, is bad news for bodybuilders since it has been shown that the amount of free amino acids both inside muscle cells and in the blood6 governs protein synthesis. This pool can be controlled very closely by a "safety valve" called "oxidation."4 By this process, the carbon skeletons from the excess amino acids are used to create energy. This can happen directly or via the synthesis of glucose [gluconeogenesis] or fat.
Another "safety valve" is the up-regulation of the enzymes in the urea cycle. This metabolic cycle takes place in the liver, and its purpose is to eliminate nitrogen [from protein] by converting it into a water-soluble form called urea, which can be excreted in the urine. The urea cycle and other liver enzymes also break down excess amino acids directly.
There are also other "safety valves" or systems the body uses to maintain a constant amino acid and protein balance, but the important thing to remember is that there are a number of systems that are altered for better or worse when you follow a high-protein diet. The consequence of this is that if you habitually consume a high-protein diet, you are setting off multiple "adaptations" and alterations in how your body metabolizes protein—it influences your protein requirement.18,19 In other words, the more protein you ingest, the more you need! This may not sound so bad for a protein lover, but think twice and you will see its downside. Eventually, you will need such a high protein intake in order to generate the positive effects that health problems could occur.
Another consideration is a large amount of protein supplements could be necessary to meet the extraordinary protein requirement you've built up.
And, perhaps most importantly, if you develop this need for a high amount of protein and you miss a meal or during your long overnight fast [the time you don't eat while you're sleeping], your body is quickly thrown into a protein catabolic state. You literally have to eat protein every few hours in order to not go "catabolic."
As we've discussed in previous articles, your body has the ability to adapt to almost anything you subject it to. For example, those individuals [probably not Muscle Media readers] who consume alcohol habitually experience an up-regulation in certain enzymes that metabolize alcohol; thus, the more frequently they drink, the more they need to consume to get intoxicated [drunk]. Follow me?
What you're saying is if I consume 400 grams of protein every day, initially this might cause an anabolic effect, but eventually, if I keep doing this, I'll need 400 grams of protein a day just to maintain my current level of muscle mass. Is this what you're saying?
Exactly. The body adapts by up-regulating enzymes and systems that break down amino acids.
At first glance, a diet dominated by protein seems to be the logical choice for every bodybuilder. After all, there are reasons this macronutrient is called protein—it's Greek for "of prime importance."
In addition to carbon, hydrogen, and oxygen, protein contains nitrogen and some sulfur, which make it different from fats and carbohydrates.
Protein can be used to create carbohydrates, and with some difficulties, it can be converted to fat, but carbohydrates and fats can never be turned into proteins unless nitrogen is present, and as we've already discussed, nitrogen comes only from protein.
Strangely enough, the current United States Recommended Daily Allowance (RDA) does not include an additional amount of protein for those who regularly engage in physical exercise.15 Several recent studies, however, indicate that dietary protein intake in excess of the current RDA [.8 g/kgBW/d—that's only 72 grams a day for a 200-lb bodybuilder] is likely needed for optimal muscle growth. For example, in one study, heavy resistance-training young adult men consuming 3.3 g/kgBW/d [which is about 300 grams per day for a 200-lb guy] versus 1.3 [about 120 grams a day] gained 2.2 more pounds of bodyweight in just 14 days4!
Another study found protein synthesis in strength-training subjects went up when protein intake was increased from .9 to 2.4 g/kgBW/d.21 These studies concluded that 2.4 and 3.3 g/kgBW/d, respectively, were in excess of the amount needed for optimal muscle growth. For example, in the study using 3.3 g/kgBW/d, the "safety valve," called oxidation, increased by 159%.4 These and other researchers now think that the "optimal" protein intake for strength-training athletes might be 1.8 g/kgBW/d11,21 [about 160 grams of protein for a 200-lb lifter].
I strongly disagree with this theory. I do not believe the subjects who put on an additional 2.2 lbs of mass in 14 days by increasing their protein intake to 3.3 g/kgBW/d4 would have been equally successful if they had increased it only to 1.8 g/kgBW/d.
I think the answer lies in how we would define the word "optimal." For bodybuilders, it means maximum muscle growth, while for scientists, it means, more or less, the level at which "safety valves" are induced disproportionately to increased protein intake.25 This discrepancy can be explained within the anabolic drive theory, which was developed by a scientist named D.J. Millward, who has developed other interesting theories on muscle growth which we've discussed in earlier parts of this article series.
Dr. Millward believes dietary protein is a key active nutritional regulator. In short, his anabolic drive theory states that "excessive dietary indispensable [essential] amino acids, prior to their oxidation, exert an important transient regulatory influence on growth, development, and protein turnover, through their activation of various hormonal and metabolic responses, which collectively constitute the anabolic drive."12
The response he's referring to consists of an increase in anabolic hormones, including thyroid hormone [T3] which, in small amounts, is anabolic in muscle tissue. The metabolic response is a direct effect of enzymes stimulating protein synthesis and inhibiting protein degradation.
Notice that Millward mentioned this is a transient phenomenon, giving evidence that the anabolic drive theory is very much in line with my protein cycling theory.
Basically, what it all amounts to is that there are pros and cons associated with a high protein intake—the way to get the positive without the negative is to cycle protein intake.
1 G. Bounous, et al., "The Influence of Dietary Whey Protein on Tissue Glutathione and the Diseases of Aging," Clin. Invest. Med. 12.6 (1989) : 343-349.
2 F. Carraro, et al., "Urea Kinetics in Humans at Two Levels of Exercise Intensity," J. Appl. Physiol. 75.3 (1993) : 1180-1185.
3 E. Estornell, et al., "Improved Nitrogen Metabolism in Rats Fed on Lipid-Rich Liquid Diets," Br. J. Nutr. 71.3 (1994) : 361-373.
4 E.B. Fern, et al., "Effects of Exaggerated Amino Acid and Protein Supply in Man," Experientia 47.2 (1991) : 168-172.
5 G.B. Forbes, et al., "Hormonal Response to Overfeeding," Am. J. Clin. Nutr. 49.4 (1989) : 608-611.
6 D.A. Fryburg, et al., "Insulin and Insulin-Like Growth Factor-1 Enhance Human Skeletal Muscle Protein Anabolism During Hyperaminoacidemia by Different Mechanisms," J. Clin. Invest. 96.4 (1995) : 1722-1729.
7 P.J. Garlick, et al., "The Effect of Protein Deprivation and Starvation on the Rate of Protein Synthesis in Tissue of the Rat," Biochim. Biophys. Acta 414.1 (1975) : 71-84.
8 N.R. Gibson, et al., "Influences of Dietary Energy and Protein on Leucine Kinetics During Feeding in Healthy Adults," Am. J. Physiol. 270.2 (1996) : E282-291.
9 A.A. Jackson, "Nutrition Adaptation in Disease and Recovery," Nutritional Adaptation in Man, eds. Sir K.L. Blaxter and J.C. Waterlow (London: Libbey, 1985) 111-126.
10 M. Langran, et al., "Adaptation to a Diet Low in Protein: Effect of Complex Carbohydrate Upon Urea Kinetics in Normal Man," Clin. Sci. 82.2 (1992) : 191-198.
11 P.W. Lemon, et al., "Protein Requirements and Muscle Mass/Strength Changes During Intensive Training in Novice Bodybuilders," J. Appl. Physiol. 73.2 (1992) : 767-775.
12 D.J. Millward and J.P.W. Rivers, "The Need for Indispensable Amino Acids: The Concept of the Anabolic Drive," Diabetes Metab. Rev. 5.2 (1989) : 191-211.
13 C. Moundras, et al., "Dietary Protein Paradox: Decrease of Amino Acid Availability Induced by High-Protein Diets," Am. J. Physiol. 264.6 Pt. 1 (1993) : G1057-1065.
14 H.N. Munro, "General Aspects of the Regulation of Protein Metabolism By Diet and Hormones," Mammalian Protein Metabolism, Vol. 3, eds. H.N. Munro and J.B. Allison (New York: Academic Press, 1964) 381-481.
15 National Research Council, Recommended Daily Allowances, Vol. 10 (Washington, D.C.: National Academy Press, 1989) 52-77.
16 P.J. Pacy, et al., "Nitrogen Homeostasis in Man: The Diurnal Responses of Protein Synthesis and Degradation and Amino Acid Oxidation to Diets With Increasing Protein Intakes," Clin. Sci. 86.1 (1994) : 103-116.
17 J. Peret, "Nitrogen Excretion on Complete Fasting and on a Nitrogen-Free Diet-Endogenous Protein," Protein and Amino Acid Functions, ed. E.J. Bigwood (Oxford: Pergamon Press, 1972) 73-118.
18 G.M. Price, et al., "Nitrogen Homeostasis in Man: Influence of Protein Intake on the Amplitude of Diurnal Cycling of Body Nitrogen," Clin. Sci. 86.1 (1994) : 91-102.
19 M.R. Quevedo, et al., "Nitrogen Homeostasis in Man: Diurnal Changes in Nitrogen Excretion, Leucine Oxidation and Whole Body Leucine Kinetics During a Reduction From a High to a Moderate Protein Intake," Clin. Sci. 86.2 (1994) : 185-193.
20 S.M. Robinson, et al., "Protein Turnover and Thermogenesis in Response to High-Protein and High-Carbohydrate Feeding in Men," Am. J. Clin. Nutr. 52.1 (1990) : 72-80.
21 M.A. Tarnopolsky, et al., "Evaluation of Protein Requirements for Trained Strength Athletes," J. Appl. Physiol. 73.5 (1992) : 1986-1995.
22 M.A. Tarnopolsky, et al., "Influence of Protein Intake and Training Status on Nitrogen Balance and Lean Body Mass," J. Appl. Physiol. 64.1 (1988) : 187-193.
23 N.E. Tawa, Jr., and A.L. Goldberg, "Suppression of Muscle Protein Turnover and Amino Acid Degradation by Dietary Protein Deficiency," Am. J. Physiol. 263.2 (1992) : E317-325.
24 J.C. Waterlow, et al., Protein Turnover in Mammalian Tissue and in the Whole Body (New York: North-Holland, 1978).
25 V.R. Young, et al., "Whole Body Protein and Amino Acid Metabolism: Relation to Protein Quality Evaluation in Human Nutrition," J. Agric. Food Chem. 29.3 (1981) : 440-447.