From athletes to dieters, high protein diets and their promises of muscle gain, weight loss and improved health appeal to a wide diversity of people. But how much and what kind of protein is best, and does the macronutrient fulfill its promises? 

While low-carbohydrate/high-protein diets, such as the Atkins or South Beach plans, are no longer the hottest trend, high-protein diets seem to be just as good (if not better) as high-carbohydrate diets for weight loss and health benefits. A high-protein diet can even help to optimize athletic performance (and muscle strengthening) due to the important role of protein in both endurance and resistance training exercise. The two modes of exercise stimulate muscle protein synthesis which is further enhanced if protein is consumed around the time of the physical activity. Eating protein immediately after exercising helps in the repair and synthesis of muscle proteins. Protein intake during exercise probably does not offer any additional performance benefit if sufficient amounts of carbohydrate – the body’s preferred energy source – are consumed.  However, for endurance athletes who need to consume adequate calories to fuel extended training sessions, or for any exerciser striving to lose weight, protein can preserve lean muscle mass and ensure that most weight loss comes from fat rather than lean tissue.

The average person requires 0.8-1.0g of protein per kilogram of body weight per day (.4-.5g/lb).  Athletes need anywhere from 1.2-1.7g/kg (0.5-0.8g/lb) depending on gender, age, and type and intensity of the exercise (less for endurance athletes and more for strength-trained athletes). The American Dietetic Association emphasizes that the recommended protein intakes are best met through diet though many athletes do turn to whey- or casein-based protein powders and other supplements to boost protein intake and muscle regeneration. 

Several factors come into play when choosing the “best” type of protein, including: protein quality, health benefits, dietary restrictions, cost, convenience, taste--to name just a few. While no one type of protein is best for everyone, keep these considerations in mind:

• Protein quality varies. Casein, egg, milk, whey and soy contain all of the essential amino acids and are easily digestible and absorbed.  Fruits, vegetables, grains and nuts are incomplete proteins and must be combined over the day to ensure adequate intake of each of the essential amino acids.
  
  
• Different types of proteins are better at different times.  Many athletes turn to the milk proteins whey and casein in an effort to maximize muscle building. Whey protein – the liquid remaining after milk has been curdled and strained -- is rapidly digested resulting in short burst of amino acids into the blood stream. Whey is known for its remarkable ability to stimulate muscle protein synthesis, even more so than casein and soy. Casein – the protein which gives milk its white color and accounts for the majority of milk protein -- is slowly digested, resulting in a more prolonged release of amino acids lasting up to hours.  If the goal is for amino acids to be readily available for muscle regeneration immediately following a workout, an athlete should time protein intake accordingly to maximize muscle building and repair (such as casein-based proteins prior to exercise and whey-based proteins during and immediately following exercise.)
  
  
• More is not always better. Total daily protein intake should not be excessive and should be reasonably proportional (≈15% of total caloric intake) to carbohydrate (≈55% of total caloric intake) and fat (≈30% of total caloric intake). Protein consumption beyond recommended amounts is unlikely to result in further muscle gains because the body has a limited capacity to use amino acids to build muscle.

Ultimately, the jury is still out on the best amounts, mechanisms and methods of protein intake. However, it seems that when combined with regular exercise and an overall healthy lifestyle protein can live up to its promises of muscle gain, weight loss and improved health.