Thread: The Low-Carb Diet
04-17-2002, 07:35 AM #1
The Low-Carb Diet
The popular media has been promoting a concept for weight loss where you decrease your carbohydrate intake to very low levels to achieve enhanced fat loss. These very rigid diets are called "ketogenic" by the scientific community while the popular media refers to them by their "brand" names such Protein Power, Sugar Busters, The Carbohydrate Addicts Diet, Anabolic Diet or Dr. Atkins New Diet Revolution. However, do not be confused, this type of program is not for beginners to the fitness lifestyle. It is also important to know that many of the individuals who have made progress on these ultra rigid diets are not avid weight trainers. As such the majority of the weight these basically sedentary individuals lose is not body fat by muscle tissue as well. This represents a very big obstacle for the avid bodybuilder or physique enthusiast since their success on any diet is measured in muscle to fat ratios not by the scale alone. However, by utilizing the techniques in this article you will not only better understand the mechanisms by which a low carb diet works but how it must be modified for persons who weight train at a high level.
Keep in mind that you should only consider one of these regimens after you have already successfully utilized a more balanced diet such as one that consists of 40% protein, 40% carbohydrates and roughly 20% fat in addition to several months of weight training and cardiovascular exercise under your belt.
With that in mind, if you choose to use a high-protein, low carbohydrate diet (HP-LC Diet) in order to enhance fat loss this article will allow you to understand its benefits while avoiding the pitfalls associated with it.
So Really What is a High Protein Low Carbohydrate Diet?
The standard protocol for a high-protein, low carbohydrate diet (HP-LC Diet) is to limit daily carbohydrate intake to well less than 100 grams. The remainder of your daily calories must come from protein and fat with an emphasis on protein if you are weight training. It is no secret that when training intensity is high (and of course intensity is key to keeping or increasing muscle size) even 200 grams of carbohydrates per day for larger athletes is tremendously meager. That’s why I never recommend this type of diet to athletes’ long term. Research has shown that a high protein diet in conjunction with low carbohydrate intake creates a metabolic environment called acidosis, which is not conducive to high intensity weight training,. Moreover, a consideration of importance beyond the aspect of performance is the anabolic effect of depressed insulin secretion on muscle protein synthesis. Moderate carbohydrate intake at each meal should stimulate the proper insulin levels needed for maximum muscle protein synthesis. Over time depressed insulin secretion may halt any additional muscular progress.
However, this macronutrient profile can be useful when it is necessary to get an athlete into an accelerated fat burning state but it must be closely monitored (more on that later) and used for only 6-8 weeks. Individuals who use a low carbohydrate diet periodically need to understand how they work so that muscle tissue is spared at the expense of fat loss. In the end, periodically lowering carbohydrate intake can work to reduce body fat. Nevertheless, any good nutrition or exercise strategy can be taken to detrimental extremes. Don’t misunderstand, I realize many successful individuals (especially those who shop at www.allsportnutrition.com) live by the notion of "going for it" but in this case the end result may cause a significant loss of size, strength and overall muscularity.
How Low Carbohydrate Diets Work
If you have ever been on a HP-LC Diet or are just curious about how they work let me give you the short version. First, when you deprive your body of glucose (all carbohydrates eventually become blood glucose) it becomes necessary for your body to use alternate energy sources. This can be a very good strategy because stored body fat is an abundant alternate energy source. In fact, our ancestors did not have an endless supply of carbohydrate foodstuffs at their disposal that prompted our bodies’ to store energy for times of "glucose insufficiency". Athletes should know that the other readily available fuel source is your own skeletal muscle proteins and if you don’t do your homework your body will tear them down to make more glucose. Regardless, tapping into your fat stores provides a virtually endless supply of energy since I cannot recall anyone who is fat free.
Anyway, second on the list of low carb diet attributes is that when carbohydrate intake is decreased—so is your bodies’ secretion of the hormone insulin. Insulin is a storage hormone with the ability to "shuttle" nutrients into several of your bodies’ storage sites including muscle tissue. The dieting benefit associated with reduced insulin secretion lies in the fact that when it is over secreted it can inhibit enzymes that promote fat oxidation, and upgrade the activity of other enzymes that promote body fat accumulation. Indeed, insulin secretion seems to be highest during sleep making more sense out of the notion that carbs at bedtime are counterproductive to fat loss. True to form many of the popular low carb weight loss diets such as The Zone, Protein Power, Atkins and others, regard controlling insulin and carbohydrate intake as equally vital parts of their success equation. The important thing to note is that any diet can work short term. The trick is in knowing the mechanisms by which they work and short circuiting the downside.
The Down Side of Low Carb Dieting
If you’ve ever taken carbohydrate intake levels to between 50 and 100 grams per day you know your muscles can start looking extremely small and flat? The reason for this is that your muscle stores become severely depleted of several key components thus reducing their overall cell volume, which of course affects its size. With that in mind I’ll focus on the special needs of weight trainers that must drive muscle cell storage components upward in the face of a low carbohydrate diet. If that pertains to you then here are some factual nutritional strategies to help you maintain muscle size while achieving ultra low levels of body fat.
The Mirror-Key to Monitoring Low Carb Diet Success
Using changes in the appearance of your muscles to gauge your nutritional status and or needs is extremely useful on a low carbohydrate diet because they are very time sensitive. What I mean by this is once you understand which nutrients alter the volume of your muscles you can make adjustments literally day by day. These visible signs are more than ever significant when you understand that as a rule HP-LC Diets cause an overall loss of cell volume making the scale an unreliable measuring tool. Your visual goal will be to keep your muscles looking FIT not flat, which we will cover in detail later. If you desire muscles that are fuller, rounder and gorging with vascularity then forget using a HP-LC Diet. For that you’ll need to come off your dieting phase and incorporate a well thought out higher carb over feeding strategy. This is similar to what competitive bodybuilders do right before a competition. On the other hand, if your goal is to attain maximum muscularity and avoid looking flat and stringy then this article can get you there.
Monitoring the "appearance" of your muscles is an art form that has been practiced for years by trial and error. Hey, it’s no accident that when you look around any commercial gym all you see is a wall of mirrors. However, beauty is more than skin deep. Today science has uncovered tons of the reasons why gauging muscularity by the mirror is essential to success.
So What Do I Look For?
The main storage compound in skeletal muscle is glycogen, which is measured in millimoles per kilogram of muscle (mmol/kg). Luckily, several researchers have found some relevant data regarding glycogen stores to help athletes gauge their cell volume. Here is what we know:
An individual following a normal mixed diet will maintain glycogen levels around 80-100 mmol/kg. Athletes following a mixed diet have higher levels, around 110-130 mmol/kg, which would represent a fuller looking muscle. As a rule weight trainers and active individuals classify a normal mixed diet as 40% protein, 40% carbs, and 20% fat. So then an active individual on a HP-LC Diet should aim for "fit" looking muscles which is represented by glycogen levels around 70 mmol/kg. If you are using other cell volumizing techniques described below, your muscles should look a little fuller than non-exercising individuals on a normal mixed diet or about 85 mmol/kg. At these levels of glycogen, fat oxidation increases both at rest and during exercise. Monitoring the "appearance" of your muscles is a very non-scientific measuring tool so it is necessary to use visualization. Picture "fit" muscles on a HP-LC Diet to look about 35 % smaller in overall cell volume than when you are not dieting (see fig.1). If you’re still unclear remember how you looked when you were eating more carbs and compare that to these warning signs that tell you’re spiraling out of control:
A flat or stringy looking muscle would represent about a 70% decrease in your overall cell volume (glycogen at 40 mmol/kg). At this level workout, performance is largely impaired and protein can become an important fuel source during exercise.
Total exhaustion during exercise occurs when your muscles are about 85% under volumized (glycogen at 15-25 mmol/kg) which is not an environment conducive to favorable changes in body composition.
Cell Volumization Techniques for Low Carb Dieters
For those restricting carbohydrates, the most likely missing nutrient in your muscle cells is stored glycogen! Glycogen is the storage form of glucose (blood sugar), of which 2/3 of total glycogen stores are found in skeletal muscle (the other 1/3 being found in the liver). The glycogen found in muscle is generally used for the muscle only and not to maintain blood sugar levels. Several movement studies have shown that anaerobic threshold and power output are markedly decreased in muscles that are glycogen depleted. In addition each particle of stored glycogen dramatically increases water content inside your muscle cells, which researchers believe is part of an osmotic (water balance) signaling mechanism to regulate whole body protein metabolism.
Glutamine, Glycogen Storage and Muscle Protein Breakdown
Since glycogen is an essential component for muscular performance and cell volume, the question arises as to how can we get more inside our muscles without resorting to eating more carbohydrates. The solution here is glutamine and post exercise carbohydrate feedings. Researchers have been looking into the stimulatory effects of diets high in glutamine as a zero carbohydrate means to increase glycogen storage. Although the mechanism is not fully understood, initial work suggests that after exercise the increased availability of glutamine promotes muscle glycogen accumulation by mechanisms possibly including the diversion of glutamine carbon to glycogen,. In addition, low glutamine status is quite common for those on low carb diets due to its use an important biochemical fuel. When energy stores are depleted glutamine is released by skeletal muscle and fulfills several functions in human metabolism making this nutrient even more vital. This may be why researchers theorize that the size of the glutamine pool (intracellular glutamine stores) is part of an osmotic signaling mechanism to regulate whole body protein metabolism.
The timing of ingested carbohydrates if of great importance when trying to improve glycogen stores while staying in a desirable fat burning mode. Research again shows us that post-exercise meals can contain liberal amounts of carbohydrate without spilling carbohydrate calories over into our fat cells. This is due to the fact that up to 2 hours after intense training muscle glycogen re-synthesis takes precedence over liver and other storage sites, such as our fat cells. Several studies have shown that creatine and insulin producing carbohydrates taken post exercise will improve glycogen stores 18% more than when taking carbs alone. In addition, there is a net energy cost of about 10% (of the carbohydrate calories) in creating ATP out of glycogen. In that sense it is even wiser to ingest carbs post–exercise. I have also discussed this topic with Lyle McDonald, the author of "The Ketogenic Diet" which is an excellent reference tool for athletes on low carb diets. He has devised a simple option for low carb dieters who train with weights called Targeted Ketogenic Dieting or TKD. Basically his work validates the fact that carbs taken around 30-60 minutes before or immediately after exercise will not lessen the fat burning effects of the diet. I suggest you try it because not only it makes good sense scientifically but also your workouts will be much more intense.
Maximizing ATP Levels on Low Carb Diets
In a carbohydrate-restricted state muscle-glycogen and glutamine levels are not the only important elements that can become insufficient. Several studies have shown that dietary restrictions may weaken your muscles by causing a deficit in Phosphocreatine or PC. PC is made from creatine and phosphate and is an energy-supporting compound found inside your muscle cells. PC provides a key to energy production, necessary to perform short-term high intensity work like lifting weights or sprinting etc. When creatine is deposited into your muscle cells, water follows, thereby promoting the rehydration of your muscles after exercise, and stimulating anabolic (building) processes dependent on hydration. Increasing the water content of your cells stimulates the formation of glycogen and protein. At the same time, having more PC in our muscles means we can spare muscle glycogen and delay fatigue. That’s especially important not only for those restricting their carbohydrate intake, but also for anyone concerned about getting results from their training. Although further studies on creatine with HP-LC Dieters are needed it seems logical that maximizing ATP levels on these regimens offers many anabolic and protective mechanisms.
The importance of avoiding flat looking muscles is at the very essence of monitoring your progress on a fat loss approach such as the HP-LC Diet. Some supplements and recommendations will allow you to successfully reach your goals.
Lemon, P.R. and J.P. Mullin "Effect of initial muscle glycogen level on protein catabolism during exercise" J Appl Physiol (1980) 48: 624-629.
Langfort J, Zarzeczny R, Pilis W, Nazar K, Kaciuba-Uscitko H The effect of a low-carbohydrate diet on performance, hormonal and metabolic responses to a 30-s bout of supramaximal exercise. Eur J Appl Physiol 1997;76(2):128-33
D. Häussinger, et al., "Amino Acid Transport, Cell Volume and Regulation of Cell Growth," Mammalian Amino Acid Transport (New York: Plenum Press, 1992).
Varnier M, Leese GP, Thompson J, Rennie MJ, et al. (1995). Stimulatory effect of glutamine on glycogen accumulation in human skeletal muscle. Am. J. Physiol. 269(2), E309-E315
Nurjhan N, Bucci A, Perriello G, Stumvoll M, Dailey G, Bier DM, Toft I, Jenssen TG, Gerich JE Glutamine: a major gluconeogenic precursor and vehicle for interorgan carbon transport in man. J Clin Invest 1995 Jan;95(1):272-7
Wagenmakers AJ Protein and amino acid metabolism in human muscle. Adv Exp Med Biol 1998; 441:307-19
Maehlum S, Felig P, Wahren J Splanchnic glucose and muscle glycogen metabolism after glucose feeding during postexercise recovery Am J Physiol 1978 Sep;235(3):E255-60
Green A, Sewell D, Simpson L, Hulman E, Macdonald I, Greenhaff P. Creatine ingestion augments muscle creatine uptake and glycogen synthesis during carbohydrate feeding in man. J Physiol 1996;491:63. Abstract
Flatt JP. The biochemistry of energy expenditure. In: Bray G, ed. Recent advances in obesity research II. London: Newmann Publ, 1978:211-28
Ziegunfuss T, Lemon PWR, Rogers M, Ross R, Yarasheski K. Acute Fluid Volume Changes in Men During Three Days of Creatine Supplementation. Journal of Exercise Physiology Online. 1998;1: In press.
Green A, Simpson E, Littlewood J, Macdonald I, Greenhaff P. Carbohydrate ingestion augments creatine retention during creatine feedings in humans. Acta Physiol Scand 1996;158:195-202
Pascoe DD, Costill DL, Fink WJ, et al. (1993). Glycogen resynthesis in skeletal muscle following resistive exercise. Med Sci Sports Exerc 25(3), 349-354
Borel MJ, Williams PE, Jabbour K, Hibbard JC, Flakoll PJ Maintaining muscle protein anabolism after a metabolic stress: role of dextrose vs. amino acid availability. Am J Physiol 1997 Jan;272(1 Pt 1):E36-44
Users Browsing this Thread
There are currently 1 users browsing this thread. (0 members and 1 guests)