fitFLEX Articles - Learn, Share and Discover
The ancient Greeks recognized the value of protein when they coined the word proteios, meaning "of first importance." Different proteins exist in the various tissues throughout the body, such as muscle, skin,
cell membranes, blood, hormones, antibodies, enzymes and genetic material.
When we speak of proteins, we are really talking about amino acids, the units that proteins are made of There are 23 known amino acids, and they all contain both an amino (NH2) and an acid (COON) group; hence the name amino acid. The individual characteristics of aminos are determined by the side chain structures. Proteins are made up of various amino acid combinations, and the number of possible combinations is infinite-there are more possibilities than there are in a state lottery.
While plants can synthesize their own proteins, we humans must get them from food. Nine of the amino acids are termed essential because they must be supplied in the diet. The body can synthesize the other amino acids, the "unessential" ones, when the essential aminos and other nutrients are present. Actually, the term "unessential" isn't quite correct as applied to these other aminos, since they play vital roles in many important body processes.
If a food contains all of the essential aminos, it's a complete protein. Foods in this category include most animal-derived proteins, such as eggs, milk, meat and fish. Proteins found in fruits, vegetables and grains often lack one or more of the essential amino acids, thus making them incomplete proteins. Unbalanced proteins like these won't support growth.
The key word here is "balance." Even if you don't eat animal protein, you can still get your daily supply of aminos by combining certain grains and vegetables. Thus, vegetarians combine rice and beans to come up with a complete protein. What's important is that you get your essential aminos daily; where they come from isn't really important.
Of the major food elements only protein contains nitrogen. Carbohydrates and fats do not. When you eat excess protein, the liver processes the aminos, and the nitrogen portion is eventually excreted as urea, a waste product. If you replace all of the nitrogen that you excrete, you're in nitrogen balance; that is, your input equals your output.
If your goal is to gain muscle, you want to be in positive nitrogen balance, whereas a negative nitrogen balance usually suggests a catabolic state, such as starvation, in which you lose muscle. There are three controversial issues involving bodybuilders and protein:
o Do bodybuilders need to eat large amounts of protein to build muscle?
o Can amino acids stimulate growth hormone sufficiently to promote an anabolic effect?
o Are certain amino acids, or proteins, dangerous when consumed in large amounts?
Let's discuss each one of these in turn. Do Bodybuilders Need More Protein?
Many dietitians claim that bodybuilders and other strength athletes need no more protein than a sedentary person needs. These ideas came from early, indirect measures of protein used by strength athletes. Newer r esearch methods, such as those using radioisotope tracers of amino acids, convey a different picture.
The protein requirement of a normal adult is defined as the least amount of dietary protein that can prevent a net loss of nitrogen from the body. Basing its recommendations on nitrogen-balance studies, the National Research Council established a Recommended Dietary Allowance of 0.8 grams of protein per kilogram of bodyweight for adults over the age of 18. This figure supposedly satisfies the minimum protein needs for 97.5 percent of people.
The 0.8 grams per kilogram includes a margin of safety intended to cover the needs of all healthy people. Because of this many dietitians suggest that any additional protein intake is superfluous. What they may not be taking into consideration, however, is the fact that exercise can lead to immediate and delayed increases in protein breakdown. Recent metabolic tracer studies, for example, show that some individuals' amino acid needs may be 23 to 178 percent greater than the RDA.
Nitrogen-balance studies clearly show that factors such as growth, energy deficit and lactation increase protein needs, but they also indicate that exercise doesn't appear to increase protein needs above normal. A closer look at some of these studies reveals the discrepancy about protein needs for exercisers.
Most of the researchers who conducted these studies were unfamiliar with how athletes really train. As a result they often used as subjects rank beginners who had never touched a weight to study the value of increased protein for what the scientists referred to as "intense training." In other words, neither the subjects nor the investigators had any idea of what really makes up intense training in the world outside their cloistered academic environment.
Without a doubt many of these studies indicated that exercise that doesn't reach a certain intensity level does not increase protein requirements above normal. Unfortunately, the exercise routines used consisted of only three or four exercises, and intensity wasn't monitored. It's no surprise that protein needs didn't increase.
Those studies that did examine the protein needs of hard-training athletes often showed elevated requirements. For example, a study done 20 years ago found that a protein intake of 2 grams per kilogram of body-weight, or 250 percent of the RDA, wasn't enough to offset a negative nitrogen balance in four out of 10 weightlifters. Other studies of Soviet weightlifters suggested that protein intakes of 1.3 to 1.6 grams per kilogram are needed for athletes to avoid slipping into negative nitrogen balances.
A 1990 study showed that the protein requirement for bodybuilders who had been training for at least three years was 0.9 grams per kilogram. Beginners may actually need more protein. One study showed that beginners need about 1,5 grams per kilogram during the first month of training. The theory here is that protein needs may be higher at the start of a training program and then level off as the body learns to conserve protein after a few weeks or months.
Researcher Gail Butterfield, Ph.D., of the Palo Alto Veterans Administration Hospital in California, believes that the inflated protein requirements shown in many studies were due to the fact that the studies used beginners, and she suggested that long- term studies may in fact present a decreased protein requirement.
Another consideration involves energy intake. There's a reciprocal relationship between calories and protein. Obviously, as calories decrease, so does protein. In one study of adult men who consumed 0.57 grams of protein per kilogram of bodyweight, their nitrogen balances improved if they expended and consumed an extra 500 calories a day. This makes sense because if you don't get sufficient calories, your dietary proteins degrade at an increased rate to provide substrates, or raw material, for energy-producing processes, such as gluconeogenesis, or the conversion of proteins to glucose, in the liver.
The relationship is especially evident when the calories come from carbohydrates. Carbs have a protein-sparing action because they're preferred over protein for energy production. Nitrogen retention goes up by 2.9 milligrams per kilogram per kilocalorie when there's a 25 percent increase in energy intake because of increased curb consumption.
Metabolic tracer studies reveal a decreased whole-body protein breakdown when calorie intake increases. One study specifically looked at what happened when bodybuilders ate fewer calories but with differing proportions of' carbohydrate and protein. The it searchers looked at 19 male bodybuilders who had neither used anabolic steroids nor ever competed in a contest.
Most of these subjects had trained three to seven times a week for at least two years. They were divided into three groups: 1) a control group of five men; 2) a high-protein-moderate-carbohydrate group that averaged 1 .6 grams of protein per kilogram of bodyweight, with 50 percent of their calories coming from carbohydrates; and 3) a moderate-protein-highcarb group that averaged 0.8 grams per kilogram of protein and 70 percent of calories from carbohydrates.
The high-protein group consuming twice the RDA of protein retained more body protein than the moderate-protein-high-carb group. The researchers concluded that a high-protein intake is more effective than high carbs for retaining body protein when a person is dieting.
More recently Steven Phinney, M.D., of the University of California at Davis Medical School compared intakes of 70 grams vs. 90 grams of protein a day in women who were following very low-calorie diets for 14 to 18 weeks. The protein that the women ate, which averaged 1.5 grams per kilogram of bodyweight per day, enhanced both aerobic and anaerobic exercise functions. Based on this, Phinney suggested a protein threshold of 1.2 grams per kilogram for people who are on very low-calorie diets.
He also suggested that the aerobic capacity of people who are on diets relates more to protein than to carbohydrate intake. Still, dietitians argue that any increased protein intake above the RDA winds up as either energy or fat. They say that the body simply excretes the nitrogen part of the amino acids, which leads to nitrogen loss. Again, these assumptions are based on studies that measured nitrogen balance in sedentary people-not hard-training athletes.
One study showed that its subjects could maintain a positive nitrogen balance for at least 50 days when the protein intakes averaged 372 percent of the RDA. Under the anabolic stimulus of heavy-weight training it's not hard to imagine that someone would need an extended period of positive nitrogen balance to support increased tissue synthesis.
There are studies of strength athletes that document this notion. One investigation found that men who trained for 40 days on protein intakes that were 350 percent of the RDA had greater nitrogen retention and made better gains than another group that consumed 175 percent of the protein RDA. Another study of men who participated in a strength-training program found greater nitrogen retention in those who consumed 300 percent of the protein RDA than in the men who ate only 100 percent of the RDA.
When Romanian weightlifters increased their protein intakes from 275 to 438 percent of the RDA, they increased their strength by 5 percent and their lean mass, or muscle, by 6 percent. As for exact protein needs, this remains a controversial subject. The requirement may even be different for men and women. For example, one study found that women who exercised 1.5 hours at 65 percent of their maximum oxygen capacities had no change in urea excretion, a measure of protein breakdown, but a group of men who exercised at the same intensity showed a 30 percent increase in urea excretion.
It's not known why the men needed more protein. Recognizing that an athlete does have increased protein needs, the American Dietetic Association upwardly revised its daily protein requirement for athletes from 0.8 to 1.0 grams per kilogram of bodyweight. Most estimates of protein needs are made according to calorie intake.
Based on available data, noted researcher Peter W. R. Lemon of Kent State University in Ohio suggested that a range of 1.5 to 2.0 grams of protein per kilogram of bodyweight is sufficient for strength athletes provided that their overall energy needs are being met. This amounts to about 12 to 15 percent of daily calories.