The Metabolic Roller Coaster
When we restrict our body from getting the energy (calories) it needs, the brain gets ticked off and takes control of the situation. One of the first things the brain does is slow down the body's metabolic rate. You've likely heard this before, but let me throw some numbers at you to illustrate the point. When five middle-aged men and women followed a 500 calorie per day diet for two weeks, resting metabolism decreased by 13% (1), which equates to a 220 reduction in calories burned for most women and around 280 calories for most men each day. Also, a 15% decrease has been reported after 3 weeks of following a 450 calorie per day diet (2). I'll admit these diet practices are intense, but even when normal-weight men ate 1,000 calories/day for 2-3 weeks they experienced a 20-24% reduction in their resting metabolic rates (3). To make matters worse, studies have shown this decrease isn't solely an immediate response, but rather can last for as long as five weeks if calories are still being restricted (4). Even worse, the loss of lean (muscle) tissue is scary! In one study, two weeks of dieting resulted in a 3% loss of lean tissue (~5 pounds of muscle for a 160-pound individual) and that 3% was more than 60% of the total amount of weight that was lost (1). A second study reduced caloric intake by 50% for 3 weeks and of the lost weight, over 50% of it was muscle tissue (5). So, sure go ahead, cut your calories and watch the pounds drop on the scale, but you're losing mostly your hard-earned muscle and crashing your metabolism as well.
An easy way to help offset this response is to exercise while dieting. Some (but not all) studies have shown a modest ability of daily aerobic exercise to help offset the loss of lean tissue while cutting calories (4, 6, 7). Resistance training, however, has been shown to help minimize the loss of lean tissue that occurs while dieting (8, 9), which is largely associated with muscles' greater rate of metabolic activity when compared to fat. This difference is not as large as once thought and for this reason, recent studies have suggested that your diet may play an extremely important role in sparing your muscle tissue when restricting calories (10, 11). In this respect and since it's not recommended to just cut your calories to ridiculously low levels, eating a diet high in protein has become popular for its ability to promote weight loss and improve body composition while also improving important markers of health found in our blood, such as glucose, insulin, triglycerides and HDL cholesterol.
The exact manner in which greater protein levels promotes weight loss and improves body composition and health aren't entirely known. But researchers at the University of Illinois have published multiple studies investigating this concept (10, 12, 13). In one of their first studies, participants consumed a diet consisting of 1,700 calories each day (a much more realistic amount), which was approximately 500 calories lower than their daily needs. One of the diets provided protein and carbohydrates in a ratio of 3.5:1, meaning for every one gram of carbohydrate eaten in the diet, 3.5 grams of protein were eaten which resulted in a daily intake that provided around 1.6 grams of protein per kilogram of body mass. The other diet provided protein and carbohydrate in a ratio of 1.5:1, resulting in a protein intake of 0.8 grams of protein per kilogram of body mass each day. All other nutrient levels were similar and after 16 weeks, the authors found that the higher protein group lost significantly more weight, lost more fat and retained more muscle (10). A number of studies support these conclusions, but from a health perspective, higher protein intakes can also improve how the body responds to insulin (a key metabolic hormone linked to diabetes), reduces the amount of fat (triglycerides) in your blood and improves good (HDL) cholesterol (12). In fact one study found that in people who have high triglyceride levels the amount of weight they lost was greater when higher protein was ingested when compared to greater levels of carbohydrates (14).
So How Much Protein Do I Need?
You would think a simple, logical question like this would have an easy answer, but it doesn't. Great debate exists regarding the optimal protein and amino acid requirements (15-17). Currently, the recommended daily allowance (RDA) for protein is 0.8 grams of protein for every kilogram of body mass each day (g/kg/day) or around 60 grams of protein for a 160-pound individual. While this article is not going to turn into a long diatribe over how much protein is too much or what is the optimal amount, I will say, however, that the RDA was developed for a normal-sized person who is sedentary. If you're reading this article because you want to learn how to maximize muscle gain while minimizing fat loss and currently exercise to lose weight, build muscle or both, you are NOT one of those people! In fact, previous reports state that during catabolic conditions, such as periods of cutting or dieting (likely things you are currently doing, have done or will do), individual amino acid requirements can change markedly (15). So for those people who voluntarily expose their body and muscles to this delicate scenario (that's YOU), eating a diet with higher levels of protein and/or supplementation with amino acids and high-quality protein sources can enhance anabolic signaling and retention of lean mass.
The Amino Acid Leucine and The Role It Plays When Dieting Or Cutting Calories
Many specific nutrients found within our common protein sources such as animal meats, dairy products and nutritional supplementation are tossed around for the potential added benefit they may provide, but one nutrient has been getting as much press as the Pratt's (You know Spencer and Heidi, the punk couple that everyone loves, or hates depending on who you ask, and can seemingly find a camera at all hours of the day). That nutrient is leucine, and to nutrition geeks like myself, it is known as an essential amino acid, which means our bodies cannot produce it, so its supply to the body is 100% dependent on dietary sources (15). In the bodybuilding and weight loss worlds, leucine's status continues to rise and for good reason (18). Studies have illustrated that leucine is a powerful anticatabolic agent meaning it helps prevent the loss of precious muscle tissue (19). Leucine has also been shown to be a valuable source of fuel for muscle, which is extremely important when considering a diet phase that is cutting back on calories to help shed your excess poundage (13). Lastly, leucine operates effectively as a signal for the muscle cell to promote an anabolic (muscle-building) environment, but is also an important aspect of helping to promote optimal control over our sugar (glucose) levels in our blood (20, 21). This last aspect may likely be its most important consideration as this suggests optimal leucine intake may be important in the management of obesity, diabetes, and other metabolic conditions which hundreds of thousands develop each year (22).
Amazingly, studies involving leucine in humans for weight loss are relative scarce, but this is beginning to change. Initially, two studies using laboratory rats investigated the role of leucine in promoting optimal changes in muscle growth. When rats were supplemented with either a carbohydrate mixture or a carbohydrate mixture with added leucine, the rats who received the added leucine reported a 40% increase in protein synthesis while the carbohydrate only group experienced no such change (19). Similarly, when rats were given a diet with a 50% greater amount of leucine, but had their caloric intake reduced by 50% for 6 weeks, they were found to have greater lean mass when compared to a normal diet (23). These last two studies are great news, but research with humans is the gold standard. In this respect, a study on 25 competitive wrestlers compared the impact of a high-protein, energy-restricted diet in combination with supplementation of amino acids including leucine to a normal diet. Now some of you may not know, but wrestlers are a crazy breed. Their sport is an extremely intense form of exercise, and they combine this with prolonged periods of extreme calorie reduction to lose weight. Researchers found that when wrestlers ate the high-protein, amino acid-supplemented diet they burned greater amounts of fat and retained their muscle mass which resulted in their continued ability to produce maximal power during an exercise test (24). While most of us aren't wrestlers, these study results are impressive and certainly should make people notice of the potential for added leucine and protein to the loss of fat while maintaining their muscle mass during periods of exercising and dieting.
Prolibra®: An Advanced New Kind Of Transformational Protein
As we discussed before, several studies have reported positive effects for eating a diet high in protein (10, 11, 25), but few studies have added protein in the form of a dietary supplement to determine its ability to promote fat loss and maintain muscle mass. Recently a new study was published that did just that, and what they found was beyond exciting for those people who work tirelessly at the gym to lose weight and improve their body composition (26). Investigators guided participants through ingesting a daily diet that met American Heart Association guidelines (55% carbohydrate, 15% protein, 30% fat), but was 500 calories lower than their daily needs for a period of 12 weeks. As part of this diet, one group consumed twice daily (once before breakfast and once before dinner) a dietary supplement containing a specialized whey fraction called Prolibra® that contained high quality protein with added levels of leucine, bioactive peptides and milk calcium. What investigators found after 12 weeks was impressive, especially when considering that an exercise program was not followed. While both groups lost a similar amount of weight (and should have because they both were following a reduced calorie diet), the Prolibra group lost significantly more of their weight as fat (~8 lbs) when compared to the control subjects (~4.5 lbs). Furthermore, the Prolibra participants lost less muscle mass and overall lost almost 4 times more fat than muscle, and again this occurred with just reducing caloric intake and no exercise!
When exercising and restricting calories to melt fat and keep your muscle, added protein is extremely important but just as important may be a protein source that contains a scientifically validated formulation which includes high levels of leucine. Currently, access to Prolibra® is limited, but PRO-SOURCE was the first company to release Vectron™, a powerful, high quality product that contains Prolibra® as its protein source. While many alternatives exist regarding protein or weight loss supplements, few match the quality and research support surrounding Vectron™ and Prolibra®. Sure, you can decide to go cheap when it comes to your protein and save a few bucks, but the scientific literature speaks for itself. As more studies become available investigating the ingredients found in Vectron™, it should become clearer and clearer that adding Vectron™ to your daily regimen should be one of the first considerations you make.
This article was written by Chad Kerksick, Ph.D., an Assistant Professor of Exercise Physiology and Director of the Applied Biochemistry and Molecular Physiology Laboratory in the Health & Exercise Science department at the University of Oklahoma. Like most readers, he loves to get his fair share of exercise in the form of running, biking, swimming and lifting weights while acting like his diet doesn't need as much as improvement as it actually does. Fortunately, he loves studying and researching various exercise and nutritional interventions to help build muscle, prevent muscle loss and improve the health of not just those people who are healthy but more passionately for those that aren't.
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