Although low-carbohydrate dieting is one of the most popular approaches today, it’s nothing new to bodybuilders, who have used it since the early ’60s. Vince Gironda, perhaps the premier trainer of that era and owner of the fabled Vince’s Gym in Studio City, California, was an advocate of low-carb dieting. He used it himself when he competed in bodybuilding contests in the early 1950s.
In fact, eating that way produced such prominent vascularity and muscle striations on Vince that bodybuilding judges were confused as to how to place him. There just wasn’t anyone around then who looked like that. The bodybuilding world wasn’t ready for it.
The basis of the low-carb diet is simple: insulin control. Although insulin has numerous functions, it is primarily a storage hormone, and one of the things it helps to store is fat. The nutrient that is most potent at eliciting an insulin release is carbohydrate, particularly simple, or so-called high-glycemic-index, carb foods. They are foods that lack fiber or contain large amounts of easily digested starch that enter the blood rapidly, which triggers the release of insulin. If you eat excess calories, the insulin helps convert them into bodyfat.
Conversely, when insulin release is controlled, as occurs during a low-carb diet, the metabolic door is opened to increased use of fat as fuel—which leads to less bodyfat.
The idea of low-carb dieting dates back to the 1860s, when a corpulent man named Banting, on the advice of his doctor, cut most of the carbs from his diet and lost a lot of bodyfat. He wrote a small book about his experiences, which became a best seller. Since then numerous incarnations of the low-carb diet have appeared under various catchy names; however, they all have one thing in common: They reduce carbs to reduce insulin release.
A major controversy of low-carb dieting is the effect on physical performance. Most people are surprised to learn that carbohydrates are not essential in human nutrition. The body actually requires glucose or alternative fuel sources, such as ketones from fat metabolism, lactate and even glycerol, which makes up 10 percent of triglyceride structure. All of those can either substitute for glucose or be converted into glucose in the liver.
Among the possible substrates for the conversion to glucose are amino acids derived from protein foods—or, in a worst-case scenario, from muscle tissue. That’s one reason that higher protein is often suggested for low-carb diets. Any excess protein that you take in can be converted in the liver into glucose. In fact, about 57 percent of excess protein eaten winds up being converted into glucose, most of which is oxidized, or burned, in the liver.
Low-carb diets are well-known for producing ketosis, which involves an increased production of ketone bodies. Ketones result from the incomplete metabolism of fat. That can occur under pathological conditions, as an effect of uncontrolled diabetes, but when it happens during a low-carb diet, it is considered not only safe but also desirable. The ketones supply an alternative energy source to glucose that can be used readily by both the brain and the muscles.
In muscle, ketones exert an anticatabolic activity, helping to prevent muscle loss. Certain parts of the central nervous system, as well as red blood cells, still demand glucose, but that’s easily supplied through the conversion of excess food amino acids into glucose. Some amino acids, such a glutamine and alanine, are particularly efficient at that. Leucine, a branched-chain amino acid noted for being the primary stimulator of muscle protein synthesis, can also help to maintain blood glucose levels during a diet.
Much of the confusion about the necessity of carbs for exercise comes from research done on endurance athletes. Endurance events are far more apt to deplete muscle and liver glycogen, which we know leads to a drop in performance. Athletes refer to it as “hitting the wall,” since that’s the way it feels. Early studies that compared carbohydrate-rich diets and low-carb diets usually found that getting more carbs led to less fatigue and better performance. Indeed, recognition of that eventually led to the concept of carb loading as a way to improve performance through enhanced glycogen production in muscles.
Carb loading involved dropping to a low-carb intake first, followed by a high-carb intake, in the period leading up to an athletic event. Later versions replaced the low-carb phase with moderate carbs combined with increased activity to deplete muscle glycogen stores, which favors supercompensation once you shift to the high-carb phase.
The truth, however, is that many endurance events take a lot of time and so favor carb depletion. What about lifting weights? That involves anaerobic metabolism, which does favor the use of glucose and glycogen as energy. Indeed, studies that have measured glycogen use during weight training show muscle glycogen depletion of 24 to 40 percent, depending on how long and how intense the workout is. One study found that doing only three sets of biceps curls led to a 40 percent depletion in glycogen in the biceps. It would appear that carbs are required for optimal training intensity, since bodybuilding workouts are fueled primarily by muscle glycogen and secondarily by circulating glucose in the blood.
Even Dr. Robert Atkins, considered the guru of low-carb diets, advised that those engaged in intense exercise require some carbs. The problem is that nearly all studies that have found a drop in exercise performance on low-carb diets were short term, lasting from three days to two weeks. It takes some time for the body to make a metabolic switch from using mainly carbs to other fuel sources, such as ketones. During the initial few days on a severely restricted carb intake, most people will experience premature fatigue during high-intensity training. Typically, you feel fine during the first set but fade considerably during the second and succeeding sets. That relates to a depletion in muscle glycogen brought on by eliminating carbs.
After three to four weeks on even a ketogenic diet (30 grams or less a day of carbs), the body adjusts to using alternative fuel sources, mainly ketones. When that happens, training becomes significantly easier, although never as efficient as when the muscles are fully loaded with glycogen. An important point here is that if you eat carbs intermittently during the initial changeover, the body doesn’t efficiently adjust to the alternative fuels. A common practice among bodybuilders is to have a carb day once or twice a week when they’re on a low-carb or ketogenic diet, the rationale being to help replace depleted glycogen and enable them to train harder. While that works, it also prevents the full adjustment to using ketones and other alternative energy sources. The net effect is that fat loss slows a bit—but not enough to offset the benefits of the diet on body composition.
A lot of the stress of low-carb dieting could be relieved by taking into account the fact that it takes about a month for the body to adjust to using fuel sources other than carbs. Much of the initial fatigue and weakness that occurs results from a diuretic effect induced by the diet. Since each gram of glycogen is stored with 2.7 grams of water, when glycogen begins to break down in response to the lack of carbs, the water is excreted. Along with it go electrolytes, minerals that are vital to muscle function, mainly sodium, potassium and magnesium. It’s the loss of those minerals that produces the feelings of fatigue at the start of low-carb diets. The easy remedy is to make sure you take in three to four grams of sodium a day, along with at least 1,000 milligrams of potassium and 600 milligrams of magnesium, which is required to retain the potassium in muscle.
Another way to avoid problems during low-carb diets is to make sure you get enough protein. You need to increase protein intake during low-calorie and low-carb diets to prevent losing muscle. Getting more protein also provides a satiety effect, reducing appetite and making the diet a bit easier. In practical terms, we’re talking about a gram of protein per pound of bodyweight per day.
Getting too much protein, however, will prevent ketosis, since the excess will be converted into glucose. The extra protein will not slow the diet progress, however, since most of it will be oxidized in the liver.
A recent study of elite artistic gymnasts compared the effects of eating a diet containing less than 20 grams of carb a day with a typical high-fat, high-carb Western diet for 30 days.1 Of interest to bodybuilders, it focused on any negative effects of the low-carb plan on strength and power performance. The gymnasts underwent various tests of strength and power both before and after the test period.
At the end of 30 days the results showed no performance differences between the ketogenic diet and the high-carb, high-fat Western diet. The gymnasts did, however, supplement both sodium and potassium, as well as taking several other vitamin and mineral supplements and herbs. They also ate a high-protein diet: 2.8 grams per kilogram—2.2 pounds—of bodyweight.
Should you consider staying on low carbs year-round? While it’s definitely the way to go in terms of losing excess bodyfat, the diet is not ideal for building muscle. If you stay on it and avoid carb days, you won’t get the benefits of insulin, which include an anticatabolic action in muscle as well as an anabolic effect in the presence of high blood amino acids. In addition, you need some carb for muscle glycogen repletion. Without it, your muscles won’t fully recover between training sessions. While ketones and other sources of energy, such as lactate and glycerol, can help to replete depleted muscle glycogen stores, that may not be enough for many people.
Carbs also promote the activity of intramuscular IGF-1, an anabolic hormone required for complete muscle recovery and growth. Last, but not least, for long-term high-intensity training, nothing beats carbs as an energy source and for preventing premature muscle fatigue. The optimal intake of carbs for nondieting bodybuilding purposes is four to seven grams per kilogram of bodyweight daily, depending on body size and how much training you do.
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1 Paoli, A., et al. (2012). Ketogenic diet does not affect strength performance in elite artistic gymnasts. J Int Soc Sports Nut. 9:34.