Protein plays numerous roles in the athlete’s body but unlike carbohydrates and fat, protein is not a primary energy source. Protein’s job is to build and maintain muscle mass and to help regulate metabolism. These functions are by no means less important than energy production, but since the body does not store protein efficiently, it is needed in smaller amounts than the other macronutrients.
Amino acids are the building blocks of proteins. There are twenty unique amino acids that combine in various ways to form the proteins that the body requires. Nine of these amino acids are dubbed “essential” meaning they must be obtained from the diet. The remaining 11 amino acids are “nonessential” meaning they can be produced by the body. Under certain circumstances, the body’s demand for some of these nonessential amino acids is too great and more is needed from the diet, these are referred to as “conditionally essential” (see Table 4.1). Leucine, isoleucine, and valine (also referred to as the branched-chain amino acids (BCAAs)) contribute most significantly to muscle tissue.
|Essential Amino Acids||Nonessential Amino Acids|
Functions of Protein
The primary functions of protein are the formation and repair of muscle tissue, enzyme production, and regulation of metabolism. Protein can be an energy source during exercise when needed but is not a very efficient way to produce energy. Proteins and amino acids are also involved in hormone and immune function, as well as fluid and acid-base balance.
Dietary protein is broken down into individual amino acids, which are then mixed and matched as needed to satisfy the body’s protein needs. Since excess protein is not stored, residual amino acids are broken down and most are removed from the body. Some remnants are utilized while the rest is excreted in the urine.
Protein in the Athlete’s Diet
Healthy sources of dietary protein include lean cuts of beef, pork poultry, fish, eggs, legumes, and soy products. Dairy like cottage cheese, milk, and Greek-style yogurt are also particularly high in protein. Protein from animal sources contains all nine essential amino acids and is referred to as “complete.” “Incomplete” proteins are missing one or more of the essential amino acids and are found mostly in plant-based proteins. Soy would be the exception; it is a plant-based complete protein. In order to get all the necessary amino acids from plant sources, it is important to eat a wide variety of foods. Combining foods like grains and legumes (like rice and beans, for example) will provide all necessary amino acids. Athletes who don’t eat meat and other animal products should be aware of these combinations and make efforts to eat them often.
When looking at protein as a percentage of overall calories, the recommendation is 10 to 35% of total intake. How are we doing with that recommendation? A paper published in the American Journal of Clinical Nutrition, titled “Current protein intake in America: analysis of the National Health and Nutrition Examination Survey, 2003-2004” found that on average, males and females, 19-70 years of age, eat approximately 15% of total calories from protein. Certainly, that is within the 10 to 35% recommendation, yet as the author of the paper suggests “given the positive benefits of higher protein intake on satiety and other physiologic functions, efforts should be undertaken to help Americans consume the recommended amounts of protein… it makes sense to consider increasing protein intake recommendations even further, to 25–30% of calories, a level that is still within the AMDR.”
Examining intake even further, since the AMDR is a large range, The Institute of Medicine’s Dietary Reference Intakes (DRI) for protein include the Recommended Dietary Allowance (RDA), Estimated Average Requirement (EAR) and the Adequate Intake (AI). These DRI’s were based on nitrogen balance studies, under conditions of energy balance. Out of the collective term DRI, most are familiar with the RDA. That being said, the current RDA for all adults aged 19 years of age or more is set at 0.8 g/kg of body weight.
However, protein experts like Stu Phillips, PhD, FACSM, FACN, Professor at McMaster University feel “that level of protein – 0.8 g/kg/d or the RDA – is the minimal level of protein to offset negative nitrogen balance in 98% of individuals. The RDA is really, in my opinion, the MDI – minimal dietary intake. Thus, nothing about that level should be recommended and you’re allowed to eat much more. In fact, for older persons and athletes there are benefits to consuming protein at levels above the RDA”
Protein Intake and Timing
More recently, protein research has moved beyond examining the optimal amount of protein to eat to examine the optimal times to eat protein. Doug Paddon-Jones, Ph.D., Professor at The University of Texas Medical Branch, has spearheaded much of this research with his work in an aging population. His (and others) work has found most Western diets skew protein consumption towards the evening meal – breakfast is typically carbohydrate-rich and protein poor, while the evening meal is often much higher in protein and calories.
In fact, some of the National Institutes of Health and Nutrition Examination Survey data regarding protein consumption in the US demonstrates that men typically only consume about 15 grams of protein at breakfast, while women consume about 10 grams. However, it’s also important to note that only about 40% of Americans are actually eating breakfast. Thus, not only are many Americans consuming low protein breakfasts, but the majority aren’t consuming anything at all. And, there is increasing evidence illustrating a causal role of breakfast (skipping) and obesity.
This unbalanced protein intake doesn’t quite give the hard-working muscles what they need nor does it do the job of helping curb appetite throughout the day. “Unlike fat or carbohydrate, the body has limited capacity to store excess dietary protein/amino acids from a single meal and use them to stimulate muscle growth at a later time,” says Paddon-Jones. He continues, “In other words, your large salmon dinner tonight is probably not going to influence muscle growth at lunch tomorrow.”
His and other experts’ theory, based on their research, is to distribute protein evenly throughout the day. “It makes perfect sense,” says Dr. Phillips, “You’ve just gone 10 hours without food… your muscles are catabolic. Protein at breakfast gives your muscles their first chance to rebuild after you’ve slept. It’s a good idea to aim for around 20g of protein if you’re younger or 30-40g if you’re older to give your muscle its best chance to rebuild since these doses of protein are at the top-end of what your muscles need.”
This balanced concept suggests a moderate amount of high-quality protein three times per day may be better than the typical Western Diet pattern suggested above. The balanced protein distribution concept isn’t just about muscle growth and repair, though. It has the potential to impact many health outcomes, such as blood sugar control, moderate calorie intake and satiety (filling you up). Of course being more full may help with how much a person eats. If you’re full and eat less, theoretically that could play a role to help with weight loss.
Assistant Professor at the University of Missouri, Heather Leidy, Ph.D. has done a lot of the work in the area of protein and satiety. Her group recently completed a 12-week long-term randomized controlled trial study comparing the daily consumption of a normal protein vs. a high protein breakfast in those who habitually skip the morning meal. This study illustrated that the daily addition of a high protein breakfast, containing 35 g of protein, prevented gains in body fat compared to those who continued to skip breakfast. However, eating a normal protein breakfast did not prevent fat gains. In addition, only the high protein breakfast led to voluntary reductions in daily food intake of ~400 kcals and reduced daily hunger. According to Dr. Leidy, “These data suggest that a simple dietary strategy of eating a protein-packed breakfast can improve weight management.”
When discussing a “protein packed breakfast,” the RDA for protein or any protein recommendation, the quality certainly matters. While a formal definition of “high quality” protein doesn’t exist, there are many methods to determine dietary protein quality. Generally speaking, complete proteins that provide all the essential amino acids are considered “high quality.” These include foods like eggs, fish, beef, poultry, dairy (including milk, cottage cheese, Greek yogurt, whey protein, and others) and soy. However, there does seem to be one amino acid – leucine – that stands head and shoulders above all others.
Leucine: Is this Protein’s “Magic Bullet”
One commonality among the foods listed above is they are each quality sources of the amino acid leucine. What is leucine and why does it matter?
Protein is made up of amino acids. As discussed, among the 20 amino acids, nine are considered essential amino acids, meaning our body doesn’t make them so we need to get them from food. Of those nine amino acids, three are called branched-chain amino acids, one of which is leucine.
Leucine is particularly interesting as the leucine concentration in a protein ultimately determines the optimal amount of protein per meal. Leucine is the “rate limiting” amino acid in muscle protein synthesis (building and maintaining muscle). Further, proteins with higher (vs lower) leucine quantities are more effective at stimulating muscle protein synthesis. One hypothesis is that there is a “leucine threshold” where protein with higher versus lower leucine quantities has more effectiveness in stimulating muscle protein synthesis. More specifically, data and consensus show that no lower than 2.2 or higher than 3.0 grams of leucine per meal is required to maximize muscle protein synthesis. These numbers are of critical importance because research suggests if a meal has less than 2.0 grams of leucine, instead of being used for muscle protein synthesis, the protein will be used for energy. This brings us back to quality, not just quantity.
Measuring Leucine Content in Foods
While it is easy to get the recommended amount (2.2 to 3.0 grams leucine) with some protein supplements, real food works too. And, sometimes even better. In fact, as you see below, cottage cheese is one of the highest food sources of leucine, providing 2.9 grams for 1 cup (about 28 grams of protein). Many others are listed below in the table.
|Food (Portion)||Leucine (grams)|
|Cottage Cheese (1 cup)|
|Chicken Breast (3 oz)|
|Ground beef (3 oz)|
|Wild Salmon (3 oz)|
|Whole egg (1)|
|Skim milk (1 cup)|
Meeting Daily Protein Needs
The key to remember is that protein intake is not just about quantity. Remember the important part is to focus on frequency and quality of the protein itself. The goal of eating 2.2 to 3.0 grams of leucine within each meal to maximize protein synthesis and get the most out of the protein you eat can go a long way to support the benefits of protein.
Translating Research into Results
While it is important to discuss specifics about protein quantity, timing, and quality, at the end of the day, what does this mean for your clients?
- Educate and inform on eating high-quality protein options in the morning. These aren’t exclusive of other foods, but rather a complement to balance their plate.
- Suggest clients aim to eat one palmful size portion of quality protein at each meal (depending on the size of the person’s hands, this will provide approximately 20 to 30 grams or protein).
- Encourage them to decrease their portion of protein in the evening, when most people are eating significantly more than their body can benefit from.
Only a very small portion (approximately 5%) of protein in the body should be metabolized for energy. Carbohydrate intake will directly affect how protein is utilized. When there is adequate carbohydrate in the diet, protein will be reserved for its primary functions.
As mentioned in section 3, muscle tissue requires protein for repair and recovery within 30 to 60 minutes post workout. Carbohydrates should also be present to replace glycogen (stored energy in the muscle tissue). Aim for about 20-30 grams of protein after a workout and continue that pattern, which the same 20-30 grams, regularly throughout the day.
Spreading out intake allows for comfortable digestion while giving muscles a steady supply of protein during the recovery period. Suggestions for post-workout snacks include a turkey sandwich or cottage cheese with fresh fruit (for additional suggestions see Table 4.2).
Athletes often complain of not being hungry so soon after an exercise session. In these cases, liquid calories may be tolerated better. A fruit and yogurt smoothie, protein shake, or serving of chocolate milk can give athletes the nutrients they need. In a study published in a 2009 study, muscle recovery was improved in soccer players who drank chocolate milk post workout.
Recovery Snacks: Winning Combinations of Carbs and Protein
- Protein is needed to form and build muscles and regulate metabolism
- The building blocks of protein are numerous essential and nonessential amino acids
- Sources include lean meat, fish, poultry, dairy, eggs, and legumes (among others)
- Daily needs are 1.2 to 1.7 grams per kilogram body weight
- Aim to eat 20-30 grams of quality protein with each meal