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Prior to this final installment, we have presented the rationale for experimenting with protein cycling given that one cannot increase one’s protein intake indefinitely to offset parallel decreases in nitrogen-retention efficiency. So, it is with pleasure that we review some proposed protocols for protein cycling. We’ll also present some personal observations with regard to dietary adaptation.

None of the protocols for cycling protein intake have been put forth in scientific journals, although there is scientific literature to buttress some of the proponent’s arguments. To date, body building literature has served as the main vehicle for conveying thoughts on protein cycling. In fact, we are not aware of any discussions of this subject in scientific circles.

Torbjorn Ackerfeldt (1) eloquently proposed a well-supported system of protein cycling and may have been the first author to resurrect the concept in many years. According to Ackerfeldt, because the "primed condition" following the low-protein phase lasts only 2-3 days, he proposes an acutely undulating model whereby a high-protein diet is consumed for 3 days followed by a low-protein diet for 3 days. The cycle then repeats itself. He recommends consuming 3.3 g protein/kg body wt/day on the high-protein days and 1.1 g protein/kg body wt/day on the low-protein days. He recommends consuming very high-quality protein on the low-protein days to maintain levels of glutathione, an important antioxidant. Furthermore, his training recommendations include no weighttraining on the first low-protein day and no aerobic exercise on the second morning. Total caloric consumption is to remain constant, increasing carbohydrate and fat intake on low-protein days to maintain adequate energy intake. Finally, he recommends consuming plenty of water (about 120 oz/day), particularly on the high-protein days. Ackerfeldt does not address the effect of meal frequency and neglects to consider that body builders typically consume very high-quality protein which would allow body builders to consume even less protein during the low-protein days. For example, the RDA for protein (.8 g/kg body wt/day) could be cut by more than half if only egg protein were consumed (2).

Marcus Jones (3) presents a more extreme form of protein cycling. Jones recommends reducing current protein intake by 50% per week until a goal of 20-40 g of protein per day is attained. Deleted calories from reduced protein are replaced only 1/2 to 2/3 with calories from carbohydrates, unless weight loss is noted for more than 4 days. According to Jones, the low-protein phase should last 4 weeks. The protein repletion phase is characterized by consuming 1 g protein/lb body wt/day. For comparison to Ackerfeldt’s recommendation expressed in kilograms, this corresponds to 2.2 g protein/kg body wt/day. Jones suggests the high-protein phase to have a duration of 4-8 weeks until a plateau in progress is reached. He does address the issue of protein feeding frequency, suggesting 4-6 meals during the high protein phase, but offers no suggestions as to how to adjust this variable for the low protein phase. He recommends ingesting protein immediately following training. In the interest of long-term health, one goal of Jones’s protocol by enhancing efficiency of protein utilization is to permanently reduce the maximum quantity of protein ingested compared to protein consumption prior to embarking on protein cycling. Jones doesn’t make specific protein recommendations for the low-protein phase relative to body weight. How does one determine whether to eat 20 or 40 g protein/day? Neither does he address how to alter training volume, intensity, etc. during the various phases. Jones’s article has more hyperbole than the other publications, and he places much emphasis on the effects of protein cycling on growth hormone. Contrary to the widespread belief in the body building community, growth hormone--even at pharmacological doses--has little, if anything, to do with muscle growth in adult humans with or without the presence of resistance exercise, and this viewpoint is supported by several scientific reviews (4-8). (Growth hormone’s mediator, circulating insulin-like growth factor 1 (IGF-1), is equally unimportant in exercise-induced muscle hypertrophy. It’s all about autocrine and paracrine IGF-1 secretion within the muscle, folks!)

One of the authors most critical of the concept of protein cycling is Lyle McDonald, who voiced several criticisms of Jones’s published protocol (9). In his own review of protein metabolism, McDonald (10) discusses protein adaptation studies in animal and human models within the context of protein cycling. He states, "the above data supports [sic] the idea of short (3-12 day cycles of alternating protein intake) far more than it does the idea of a full month of low-protein." McDonald goes on to conclude, "...not only does the body appear to first replete those proteins which were first lost (liver and other organ proteins), but by the time those proteins are repleted, the body has readapted to the current level of protein intake." In the end, McDonald recommends 1 g protein/lb body wt/day or "slightly less." In contrast, we would propose that if copious protein is abruptly consumed during repletion, then there would be enough protein for both restoration of organ stores as well as muscle growth, although this is hypothetical. McDonald’s final recommendation does not address the possibility that by slowly decreasing protein intake over time, a lower-protein diet would work equally well as maintaining a high-protein intake. We recommend McDonald’s series as a well-referenced, thorough review of protein metabolism.

It should be emphasized that any evidence that results from documentation of the effects of any of these protocols is going to be very indirect evidence. For example, increased muscle size and strength is going to be a result of enhanced nitrogen retention which in turn is dependent on the enzymes responsible for protein anabolism or catabolism. Since the increase or decrease in efficiency of protein metabolism is enzyme mediated--both the protein oxidation and protein storage--maybe a better understanding of the time course for enzyme production is what is required for the concept of protein cycling to advance beyond its speculative infancy. Because the half-lives of the catabolic and anabolic enzymes are different, it seems that understanding the enzymes is the key to understanding the proper time course for protein cycling. Perhaps some skinny enzyme biochemist in a hidden laboratory holds key information in this regard.

Clinical investigation of protein cycling, if ever taken seriously by nutrition researchers, could prove very difficult to generate conclusive findings. The difficulty lies in the multitude of possible combinations of daily protein intake (i.e., how low and high should you go?), protein quality, frequency of protein feedings, concurrent caloric consumption, and cycle duration (i.e., how long should each phase last?). Thus, whatever data are generated will have to be viewed cautiously because a lack of benefit to protein cycling could actually be attributed to the exact implementation of the protein cycling protocol rather than the ineffectiveness of protein cycling per se. Just one mismanipulated variable could sabotage the outcomes of the cycling. Much tinkering may be involved in fine-tuning the manipulated variables so that a fruitful combination is achieved. In the meantime, it appears that self-experimentation based on the broad guidelines presented above is the only avenue for individual self-discovery as to the possible benefits of protein cycling.

One of us (D.S.) has engaged in such self-experimentation. We want to make it very clear that these are merely reflections and NOT the result of research and do NOT represent conclusive statements. For "fun," he has tinkered with the protocol of Jones. After the first three weeks of cycling, he reports, "I was VERY hungry the first 2 weeks of decreasing protein cycles (240 g protein/day to 120 g protein/day during week 1, then from 120 g protein/day to 60 g protein/day during week 2). To counteract this hunger, I had to increase carbohydrate levels by at least the same number of grams by which protein was reduced. During the third week, this feeling of hunger subsided, and I was able to reduce my carbohydrate levels some, but did crave a steak or hamburger. My strength remained unaffected..."

Dave, in his 25 years of experience in bodybuilding, has also observed that periods of rapid progress in growth or training seem to occur in three week cycles. For example, his training partner, a powerlifter, recently increased his calorie and protein intake by roughly 30% which yielded strength and weight gains for about three weeks until plateauing. He has observed that after anabolic steroids "kick-in" (usually 2 weeks following pharmacological intervention), the best gains occur for the next three weeks. He notes that after dieting for a bodybuilding contest for 8-12 weeks, upon resuming a normal diet he experiences a surge in growth and strength that lasts 2-3 weeks. Given these observations he reports, "My unresearched, untested ‘gut feel’ is that we are going to see a 10-20 day time frame for complete adaptation, whether it’s to high or low levels of protein consumption."

As you can see, the opinions regarding protein cycling in bodybuilding are many and varied. Regardless of what protein cycling protocol you may choose, document all of your practices carefully so that others and yourself may learn from your self-experimentation. Good luck!

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Dr. Greg Bradley-Popovich holds dual master's degrees in Exercise Physiology and Human Nutrition from West Virginia University as well as a doctorate in Physical Therapy from Creighton University. He is the Director of Clinical Research at Northwest Spine Management, Rehabilitation, and Sports Conditioning in Portland, Oregon.

1. Phillips B. Get ready to grow big time: Part IV of the anabolic burst cycling system: How protein cycling may enhance muscle growth. Muscle Media 1997;61(Aug):100-109.

2. Williams MH. Nutrition for fitness and sport. 4th ed. Dubuque, IA: Brown & Benchmark, 1995:162.

3. Jones M. Protein cycling for maximum gains. [Online]Testosterone 1998;10. www.testosterone.net/html/10maxim.html [1999, Nov 7].

4. Adams G. Role of insulin-like growth factor-I in the regulation of skeletal muscle adaptation to increased loading. In: J. O. Holloszy, ed. Exercise and sport sciences reviews. Baltimore, MD: Williams and Wilkins, 1998.

5. Borer KT. The effects of exercise on growth. Sports Med 1995;20:375-397.

6. Borer KT. Neurohumoral mediation of exercise-induced muscle growth. Med Sci Sport Exerc 1994;26:741-754.

7. Roemmich JM, Rogol AD. Exercise and growth hormone: Does one affect the other? J Ped 1997;131:S75-S80.

8. Zachwieja JJ, Yarasheski KE. Does growth hormone therapy in conjunction with resistance exercise increase muscle force production and muscle mass in men and women aged 60 years or older? Phys Ther 1999;79:76-82.

9. Jones M. Protein cycling revisited. [Online]Testosterone 1998;19. www.testosterone.net/html/19prote.html [1999, Nov 7].

10. McDonald L. Protein, part 4: Amino acid kinetics and adaptations. [Online]Mesomorphosis 1999;2(5). www.mesomorphosis.com/exclusive/mcdonald/protein04.htm [2000, March 15].

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