Protein and Amino Acid Supplementation in Sports and Exercise

Rationale and Validity of Protein Supplementation

• General Perspective on Protein Supplements

  • Hard-training athletes require approximately $50-100\%$ more protein than sedentary individuals.

  • Significant marketing investment characterizes the protein supplement industry, yet many claims remain unjustified.

  • Most Western populations consume protein in amounts significantly higher than the Recommended Dietary Intake (RDI), often exceeding the additional needs of most athletes.

  • Scientific studies regarding protein supplements are frequently criticized for poor design or a lack of well-defined outcomes.

• Protein Metabolism During Exercise

  • Protein serves as an energy fuel more significantly than previously understood.

  • Exercise triggers increased protein breakdown (catabolism), particularly in carbohydrate-depleted states, such as at the end of endurance activities.

  • Conversely, protein synthesis is augmented during the recovery phase after exercise.

  • Synthesis rises markedly post-exercise (both endurance and resistance types), especially during the early stages of a training program.

  • Re-evaluating current Recommended Daily Allowances (RDA) for heavy exercise is justified, as requirements depend on nutritional status, exercise intensity, and competition level.

  • Branched-chain amino acids (BCAAs) are particularly unique because they oxidize within skeletal muscle rather than the liver.

  • Post-exercise represents a critical window for replenishing protein lost during activity.

Types of Protein Supplements

• Whey Protein

  • The most commonly utilized supplement type.

  • Boasts a high biological value (BV).

  • Makes up $20\%$ of the protein found in milk.

  • Rich in BCAAs and possesses high satiety value, making it useful in weight loss programs.

  • Historically considered a "waste" product of the cheese industry and was often discarded.

  • Whey Protein Concentrate (WPC): The first filtrate; contains $70-80\%$ protein plus some lactose and fat. It is the most affordable form.

  • Whey Protein Isolate (WPI): Filtered WPC containing $90\%$ protein with no lactose or fat.

  • Whey Protein Hydrolysate (WPH): Produced from WPC or WPI where proteins are hydrolysed into short peptides and amino acids. It is marketed for more rapid digestion and absorption (though this is questioned), is more expensive, and has a bitter taste.

• Casein (Calcium Caseinate)

  • High biological value protein representing $80\%$ of milk protein.

  • Clots in the stomach, which slows digestion and the subsequent delivery of amino acids into the bloodstream.

  • Hydrolysates are available for those seeking faster delivery.

• Soy Protein

  • High biological value and rapidly digested.

  • Frequently found in mixed supplements and protein bars; generally cheaper than whey.

  • Contains phytoestrogens; caution is recommended (or total avoidance) for patients with a history of breast cancer.

• Egg Albumin

  • High biological value source.

  • Fat-free and carbohydrate-free.

  • Was the primary supplement choice before whey and casein became cheaper and more accessible.

Protein Intake Recommendations and Dietary Sources

• Standard RDA and Calculations

  • Standard RDA: $0.8\,g/kg$ body mass. For a $70\,kg$ male, this equals $56\,g/day$.

  • Endurance training RDA: $1.2$ to $1.4\,g/kg$ of high-quality protein per day.

  • Resistance training RDA: May benefit from up to $1.8\,g/kg$ body mass.

  • A $70\,kg$ male playing competitive football requires up to $1.7\,g/kg$ ($120\,g/day$) according to the Australian Institute of Sport (AIS).

• Australian Consumption Statistics (1995 National Nutrition Survey)

  • Average adult Australian: $91\,g/day$.

  • Average males: $109\,g/day$.

  • Average females: $74\,g/day$.

  • Since these are averages, $50\%$ of the population eats more than these amounts. Most athletes already consume adequate protein because they eat naturally larger volumes of food.

• Athletic Needs by Category

  • Endurance Athletes: Need extra protein to recover small muscle protein losses used for energy output.

  • Strength Athletes (Early Phase): Require extra protein during the muscle-gaining phase.

  • Trained Strength Athletes: Require only a marginally increased intake once muscle mass is established.

  • Adolescent Athletes: Require increased intake to support ongoing growth.

• Whole Food Equivalents (AIS/Sports Dietitians Australia)

  • Low-fat, micronutrient-rich food serves delivering $10\,g$ protein each are prioritized.

  • Example items provided by SDA deliver $20-30\,g$ protein per serve.

  • A sample AIS diet for a $70\,kg$ athlete delivering $166\,g$ protein ($2.3\,g/kg$) illustrates that most whole foods contribute to a high protein total without supplements.

Adverse Health Effects of High Protein Intake

• Dehydration: Increased urea excretion necessitates higher water loss, an important consideration for athletes. Protein digestion also consumes energy, increasing the risk of over-heating.

• Adult Bone Loss (Osteoporosis): High protein intake is associated with increased calcium excretion. Conversely, inadequate intake (e.g., elderly, anorexia) also leads to osteoporosis.

• Heart Disease: High animal protein diets often correlate with high saturated fat intake. High protein diets can elevate homocysteine levels, increasing cardiac risk. Note: Arginine may counteract this by lowering BP and homocysteine.

• Cancer: High animal protein intake is linked to cancers of the breast, colon, kidneys, pancreas, and prostate, though it is difficult to isolate protein from fat intake.

• Kidney Disease: High protein increases the workload of the kidneys. While it does not appear to cause kidney disease in healthy individuals, it can exacerbate existing conditions.

Guidelines for Supplement Use

• The Take Home Message (Sports Dietitians Australia)

  • Supplements should only be used after considering an athlete's energy requirements, training load, goals, meal plan, lifestyle, post-exercise appetite, and finances.

  • Whole foods should be a priority due to their superior micronutrient content.

  • Supplements are valued only when rapid delivery of easily digested protein is required, such as post-exercise when appetite is suppressed.

• Dosage and Recommendations

  • Limit intake to $1-2$ serves per day.

  • Individual doses should not exceed $20-30\,g$.

  • Use immediately after exercise for maximum effectiveness.

  • Whey protein is preferred for muscle mass gains due to high Leucine content, which stimulates protein synthesis.

Amino Acid Supplements: BCAAs, Arginine, and Glutamine

• Branched Chain Amino Acids (BCAAs)

  • Consist of Leucine, Isoleucine, and Valine.

  • Skeletal muscle is the primary metabolizing tissue for BCAAs (metabolism occurs in muscle rather than the liver).

  • Metabolism is regulated by BCKDH phosphorylation; exercise enhances this metabolism.

  • Study Results (Howatson et al. 2012): National league football players taking $10\,g$ twice daily (ratio $2:1:1$ Leucine:Isoleucine:Valine) for $12$ days showed reduced plasma creatine kinase, reduced muscle soreness, and improved recovery of function after $100$ drop-jumps.

  • Higher benefits may be seen in females regarding delayed onset muscle soreness (DOMS).

• L-Arginine

  • Claimed to enhance strength and power via vasodilation.

  • Rationale: Precursor to Nitric Oxide (NO) and used to produce creatine phosphate. Most studies show only modest improvements.

• Glutamine

  • Non-essential amino acid; the body creates sufficient amounts in muscle.

  • Essential fuel for gut mucosal and immune cells. Levels drop during over-training or critical illness.

  • Clinical Perspective (M Gleeson 2008): Supplementation before/after exercise showed NO benefit to immune function or fluid balance. However, it may stimulate muscle glycogen and protein synthesis.