Protein is used to repair cell injuries (muscles particularly) from the microscopic trauma that occurs with exercise. It is NOT a good energy source, and serves that purpose only in malnourished states. Even in endurance activities such as the Tour De france, protein needs of 1.5 gms protein/kg body wt/day were easily met by a normal (read unsupplemented) diet that replaced the total Calories used each day.
All protein molecules are composed of building blocks called amino acids. Most protein digestion occurs in the small intestine where protein molecules are first split into their component amino acids which are then absorbed by the intestinal lining, transported via the circulatory system, and taken up by cells throughout the body. These amino acids are then used to rebuild cell proteins. Any excess protein in the diet is transformed (metabolised) into carbohydrates (gluconeogenesis) or fat. Protein itself is not stored in the body which means cell repair occurs from protein eaten that day or from amino acids released as protein is broken down elsewhere in the body.
HOW MUCH PROTEIN DO YOU REALLY NEED?
A team of researchers from Kent State University, Ohio, and McMaster University, Ontario, led by Dr. Peter Lemon studied a group of 12 male subjects during two months of resistance training. They found that a protein intake of 81 grams per day (0.99g per kg of bodyweight for a 180 lb male) resulted in a negative nitrogen balance. Nitrogen balance is a measure of protein metabolism. A negative nitrogen balance indicates that the protein needs of the body are not being met and protein is being scavanged from tissue elsewhere in the body to maintain essential body functions. This may lead to reduced gains in muscle mass and strength.
Can you eat too much protein? This group also found that protein intakes above 2.62 grams per kg of bodyweight (214 grams for a 180lb male) provided no additional benefit in terms of nitrogen balance and increased the risk of renal overload and dehydration. Long term studies of large groups show that a high protein/low carbohydrate diet increases the risk of kidney stones and bone loss. These findings were substantiated by a University of Texas study of 10 volunteers on a high protein/low carbohydrte diet for two weeks. Blood uric acid levels (uric acid is a major cause of kidney stones) rose 90% and urinary levels of citrate (which inhibits kidney stone formation) dropped 25%. And finally, any extra protein Calories (beyond what you are expending per day) are stored as fat, not muscle.
Protein is essential for endurance athletes as well as to aid muscle development. As far back as 1983, scientists demonstrated that two hours of exercise can drain the body of essential protein stores. Based on their findings, Dr. Lemon makes the following recommendations for protein intake for strength and endurance athletes:
Strength - 1.6-1.7 grams of dietary protein per kg of bodyweight
Endurance - 1.2-1.4 grams of dietary protein per kg of bodyweight
The average 70 kg (154 pound) cyclist will need from 80 to 100 grams of protein per day. And for those at the elite level, the requirement may be as high as 1.7 grams of protein per kgm (120 grams for the ideal 70 kg rider). And as active athletes consume more daily Calories, a balanced diet without supplements will meet these increased needs.
A literature review failed to find any support for protein supplements (assuming a balnaced daily diet with the normal distribution of protein intake) compared to a pure carbohydrates diet alone. In fact there is the potential for a DECREASE in overall performance from the appetite suppressing effects of a high protein diet which results in a decrease in carbohydrate intake and diminished pre event muscle glycogen stores.
SOURCES OF PROTEIN
Lean beef, skinless chicken, and fish will provide about 7 grams of protein per ounce. Beans will provide 6 grams per 1/2 cooked cup, and rice (and other cereal grains) about 3 grams per 1/2 cup serving. A cup of milk or yogurt supplies 8 grams of protein. So it's relatively easy to meet your basic protein requirements from 6-8 ounces of meat, 2-3 servings of dairy products, and 6-10 servings of cereal per day.
A HIGH PROTEIN DIET (THE ZONE DIET)
The ZONE is basically a Calorie restricted, high protein diet used to facilitate weight loss. It has also been proposed as a nutrition strategy to improve athletic performance, reduce body fat and increase muscle mass. It recommends consuming 40% of your daily Caloric intake in the form of carbohydrate, 30% as protein, with fat making up the other 30%. An analysis should give us some insight into the effects of a high protein diet.
If you are a 60kg (132 pound) cyclist requiring 3000 Calories per day for your training program, a recommendation of 1.5 grams would translate into 90 grams of protein or 10-12% of your overall Calories (there are 4 Calories per gram of protein). However to reach 30% protein, you'd need to consume a massive 225 grams.
Here's what you'd need to eat each day:
1 cup cottage cheese-----28 grams
1 can (3oz) tuna fish----22 grams
3 glasses milk-----------24 grams
8 ounces lean beef-------66 grams
1 cup kidney beans-------13 grams
1/4 cup peanut butter----32 grams
1 chicken breast---------27 grams
3 egg whites-------------12 grams
However, Dr. Sears doesn't start with your Calorie needs (remember this is a Calorie restricted diet). He starts with your weight and then calculates you protein requirements. Dr. Sears recommends consuming between 0.8 and 1.0g of protein per pound of lean body mass. For an individual weighing 180lb, daily protein intake would work out between 127g and 158g per day. As he recommends that protein represent 30% of daily caloric intake, daily fat consumption (30% of Calories) works out to be 70g, and carbohydrate (40%) is 211g. The daily energy content of the Zone diet for this 180lb individual is approximately 2106 Calories. And that is how it helps you lose weight - the total Calories consumed using this approach is much less than an active athlete needs.
What are the problems with the Zone diet diet for an athlete? As just pointed out, the recommended carbohydrate intake for our 180lb rider was 211g of carbohydrate per day. Such a recommendation is in sharp contrast to the majority of scientific research which proves the need for adequate carbohydrate to support maximal physical performance.
For example, a recent study compared the effects of different levels of carbohydrate intake on the performance of two Swedish ice hockey team. Both teams took part in two games separated by three days. During this three-day gap, the players were assigned to one of two groups. The first group consumed a normal mixed diet that provided around 40% of energy from carbohydrate. Group two had their diet supplemented with extra carbohydrate. Energy from carbohydrate in the second group represented 60% of total energy intake. The study clearly showed an improvement in physical performance in the high carbohydrate group. Simply put, a diet containing only 40% of its calories from carbohydrate was insufficient to meet the energy needs of elite athletes.
The Zone diet's recommendations for daily protein intake are a little closer to the mark. The amount of protein required by those participating in regular exercise sessions remains a topic of considerable debate. Nevertheless, there is research to show that both endurance and strength exercise increase protein requirements.
But the Zone diet can accelerate fat loss. While it does not provide enough energy to meet the needs of a competitive athlete, it does restrict Calories and its emphasis on high levels of protein may also serve to enhance fat loss. A recent Danish study, published in the International Journal of Obesity, compared the effects of a high protein and a high carbohydrate diet on weight loss. A group of 60 subjects followed a restricted Calorie diet for six months. The participants were assigned to either a high carbohydrate or high protein diet. Those on the high protein diet consumed approximately 24% of their Calories from fat, 46% from carbohydrate, and 29% from protein. The diet for subjects on the high carbohydrate diet consisted of 28% from fat, 59% from carbohydrate, and 12% from protein. Scientists found that the high protein group lost almost twice as much fat as those on the high carbohydrate diet.
Notice the similarity between the nutrient distribution in the high protein diet (46/29/24) and the recommendations in the Zone diet (40/30/30). The group following the high protein diet consumed 11.3 Calories for every pound of bodyweight each day - similar to the 11.7 Calories per pound of bodyweight suggested by the Zone diet.
After analyzing the dietary intake of the groups, the research team realized those on the high protein diet had eaten less food. This accounted for the greater weight loss. There were several possible explanations for this reduction in food intake. Protein has a higher satiating (pronounced effect than carbohydrate. In other words, you feel less hungry when consuming a diet high in protein. And a high protein intake seems able to suppress the following days energy intake to a greater extent than carbohydrate.
The bottom line - The Zone diet is essentially a restricted calorie diet. For individuals wanting to lose body fat, there is no reason why the Zone diet would not prove effective. However it is unrealistic to expect that athletes will experience any significant improvements in performance as a result of the Zone diet. The recommendations for both carbohydrate and Caloric intakes are not sufficient to meet the energy requirements of regular daily training.Go high protein/low carbohydrate and you'll be chronically bonked.
WHAT ABOUT PROTEIN SUPPLEMENTS TO A NORMAL DIET?
In his review of the literature (original abstract) on dietary protein supplements, Dr. Richard B Kreider PhD (Department of Human Movement Sciences & Education, The University of Memphis, Memphis, Tennessee 38152. Email: firstname.lastname@example.org) concluded that "dietary supplementation of protein beyond that necessary to maintain nitrogen balance does not provide additional benefits for athletes."
Here is an excerpt of his review:
Protein and amino acids are among the most common nutritional supplements taken by athletes. This review evaluates the rationale and potential effects on athletic performance of protein, purported anabolic amino acids, branched-chain amino acids, glutamine, creatine, and hydroxymethylbutyrate (HMB). LITERATURE. Two books, 61 research articles, 10 published abstracts, and 19 review articles or book chapters. FINDINGS. Dietary supplementation of protein beyond that necessary to maintain nitrogen balance does not provide additional benefits for athletes. Ingesting carbohydrate with protein prior to or following exercise may reduce catabolism, promote glycogen resynthesis, or promote a more anabolic hormonal environment. Whether employing these strategies during training enhances performance is not yet clear. There is some evidence from clinical studies that certain amino acids (e.g., arginine, histidine, lysine, methionine, ornithine, and phenylalanine) have anabolic effects by stimulating the release of growth hormone, insulin, and/or glucocorticoids, but there is little evidence that supplementation of these amino acids enhances athletic performance. Branched-chain amino acids (leucine, isoleucine, and valine) and glutamine may be involved in exercise-induced central fatigue and immune suppression,but their ergogenic value as supplements is equivocal at present. Most studies indicate that creatine supplementation may be an effective and safe way to enhance performance in intermittent high-intensity exercise and to enhance adaptations to training. Supplementation with hydroxymethylbutyrate appears to reduce catabolism and increase gains in strength and fat-free mass in untrained individuals initiating training; as yet, limited data are available to decide how it affects training adaptations in athletes. CONCLUSIONS. Of the nutrients reviewed, creatine appears to have the greatest ergogenic potential for athletes involved in intense training. FURTHER RESEARCH. All supplements reviewed here need more evaluation for safety and effects on athletic performance.
Potential risks of excessive dietary protein or protein supplements include:
* skimping on the carbohydrates needed for muscle glycogen repletion (risking the development of chronic fatigue)
* dehydration potential kidney damage over time
* and excessive bone loss (as protein increases urinary calcium loss).
THE BOTTOM LINE
Protein is necessary for the active athlete, but more is not necessarily better. And this is especially so if you replace total Caloric needs with protein at the expense of carbohydrates.