Exercise builds muscle because it stimulates the production of more muscle protein, but it does it in conjunction with dietary factors, namely taking in essential amino acids. Aminos are the elemental forms of protein, in that protein is broken down and absorbed into the body as amino acids.
Amino acids fall into two general categories: essential and nonessential. Those classified as “essential” cannot be synthesized in the body and must be supplied in the diet. Nonessential aminos are important, but they can be produced in the body from other amino acids. Studies show that you need to take only six to 10 grams of essential amino acids after a workout to trigger the most muscle protein synthesis.
While most high protein foods, such as milk, eggs, beef and fish, are loaded with amino acids, including the essential variety, many bodybuilders still feel the need to slug down concentrated protein supplements. The most popular are those made from whey.
Whey is one of two major milk proteins, with the other being casein. Whey is particularly useful for boosting muscle protein synthesis because it’s rapidly absorbed, and studies show that getting amino acids after a workout gives you a significant head start on that score. Whey is particularly rich in essential amino acids, especially the branched-chain aminos—26 percent content in whey—which are the primary essential amino acids involved in proteins synthesis.
Besides its rich amino acid content, whey provides a number of small but active proteins called bioactive factors that are known to favorably influence health and boost immunity. Some of those factors also influence appetite, which permits easier dieting and thus more rapid fat-loss.
One reason that it’s so important for bodybuilders to maintain a high protein intake when they’re dieting is to preserve muscle. In the usual diet scenario either calories or carbohydrates or both are severely restricted. As fat loss progresses, however, there comes a point when the body starts to catabolize muscle for its amino acid content.
The amino acids then travel to the liver, where they are converted into the most readily available energy source, glucose. To avoid the whole process, it’s vital to boost protein intake. The extra protein will spare muscle protein stores, limiting your muscle loss when you’re dieting. That’s another reason why protein supplements are useful—they provide concentrated protein but without excess calories, fat or carbs that would hamper dieting efforts.
High-protein diets have been shown in numerous studies to promote greater bodyfat losses. One reason to explain that is the increased satiety, a feeling of fullness, that occurs with a high protein intake, which helps to control appetite. Some of the bioactive factors found in milk protein are also known to exert a safe, natural appetite-suppressing effect. Still, a recent study shows that merely getting added protein provides another effect favorable to fat loss: It promotes added fat oxidation, or “burning,” during exercise.
The study consisted of six men and 11 women, all of whom had shown stable weight over the prior two months. In other words, they were neither gaining nor losing weight at the start of the study. The study lasted for three months. The subjects all took in the same amount of calories, but one group got more protein. Those subjects used a milk-based protein supplement, taking it three times a day for a total of 52 extra grams of protein. The other group got a carbohydrate-and-fat concoction. The type of fat used in the drink was olive oil, which some studies show favors fat burning during exercise.
Besides the drinks, the subjects were told to eat at least 200 grams of fruit and 300 grams of vegetables. They were tested at the start of the study to determine the level of exercise that burned the maximum amount of fat. That turned out to be 51 percent of maximum oxygen intake after an overnight fast, a level that equates to a low-moderate exercise intensity.
The primary result of the study was that after three months a high-protein diet appears to stimulate both increased fat oxidation and increased muscle without any change in either bodyweight or exercise activity.
The authors noted that getting more protein causes a shift in the balance of energy substrates, with an increase in protein balance and a decrease in fat balance. In short, eating more protein causes more protein to be deposited in muscle at the expense of fat stores. The fat was released from fat cells into the blood, where it was burned during exercise. It also blocked the entry of fat into fat cells. Having a greater amount of fat-free mass, or muscle, increased overall energy expenditure, since fat-free mass is what determines resting energy expenditure. That’s one reason for the increase in bodyfat as people age. As physical activity is curtailed, fat-free mass decreases, and less energy is burned, resulting in more fat being stored.
The greater protein intake also promotes greater rates of muscle protein synthesis. Protein synthesis is an energy-intensive process, and guess where the majority of calories that power it comes from—fat. So the body actually upgrades fat burning to fuel muscle protein synthesis reactions. Fat is the primary source of energy during resting conditions, when muscle protein synthesis usually occurs. In addition, the synthesis and breakdown of muscle itself contributes to the energy expenditure of resting muscle.
So, basically, if you want to produce more muscle, take in more protein It’s the added muscle mass from the higher protein intake that enables you to burn more fat during exercise, even without a change in bodyweight. It’s a question of replacing fat with muscle, which is metabolically more active than fat.
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Soenen, S., et al. (2010). Protein intake induced an increase in exercise-stimulated fat oxidation during stable bodyweight. Phy Behav. 101:770-774.