Protein Nutrition and Exercise: What’s the Latest?
This article examines some recent developments in the field of protein nutrition for athletes, in particular those relating to muscle hypertrophy, weight loss, and recovery from intense exercise.
Protein and Muscle Hypertrophy
The metabolic basis for muscle growth is the balance between muscle protein synthesis (MPS) and breakdown. Positive net muscle protein balance occurs when synthesis exceeds breakdown over a given time period. Protein intake increases MPS; exercise, particularly resistance exercise, result in an interactive effect with the ingested protein leading to the greatest MPS. Interestingly, the interaction of exercise and protein lasts at least 24 hours.
The anabolic response to resistance exercise and protein intake depends on many factors. The amount, type, and timing of intake, other nutrients ingested concurrently, and the precise nature of the exercise all influence the response.
- Animal protein sources seem to stimulate a larger anabolic response in muscle than plant protein.
- The form of protein does not seem to make a difference; food sources and supplement sources stimulate the same response.
- Carbohydrate intake with protein has minimal impact on MPS; however, it reduces muscle protein breakdown thus improving overall balance. Adequate carbohydrate equates to about .3-.6 grams/pound body weight (ex. 160 lb person x .3-.6 = 48 – 96 gms carb) within 2 hours after exercise. A 4:1 ratio of carb to protein is ideal.
- Presence of fat may play a role; one study found MPS was greater for consumption of whole milk than skim milk but more studies are necessary to draw conclusions and make recommendations.
- Protein intake within 1 hour after exercise may slightly enhance MPS but recent studies are finding the interactive response lasts at least 24 hours. Any protein intake during that time will contribute to muscle synthesis.
- Recent findings suggest there is a limit to the amount of protein that will effectively increase the anabolic response; the response of MPS to increasing doses of protein following resistance exercise plateaus
- Response increased incrementally up to 20g (3 ounces of meat, poultry, fish, etc.) but no difference occurred in the response between 20g and 40g of protein.
Protein and Weight Loss in Athletes
Fat loss requires a caloric deficit which inherently compromises muscle growth. It is very difficult to keep MPS ahead of muscle breakdown during calorie restriction. A high protein, calorie restricted diet may be the answer. A recent study of weightlifters found the individuals cutting total energy intake to 60% of normal and eating 2.3 g pro/kg body weight or 35% total energy (at the expense of fat rather than carbohydrate) lost the same amount of fat weight as the control group [who also restricted calories to 60% of normal but ate 1.5 gm pro/kg body weight]. However, the high protein group lost little muscle while the control group lost considerable muscle.
For a 220 pound male, this diet would contain 230 grams of protein (220 lbs/2.2 = 100kgs) and 2600 calories. For a 130 pound female, this diet contains 136 grams and 1500 calories.
Protein and Recovery from Intense Exercise
Protein is beneficial for MPS and prevention of muscle breakdown but has not shown to improve muscle recovery (i.e. muscle soreness/muscle function). There is some evidence that a high protein diet might prevent the effects of overtraining in endurance athletes but may not outweigh the negative impact of reduced carbohydrate intake in these athletes.
Summary of an article from the Spring 2011 edition of the Sports and Cardiovascular Nutrition PULSE Newsletter; author: Kevin D. Tipton, PhD.