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Protein Requirements

Protein is a nutrient that is essential for growth and development. It is the second most abundant compound in the body after water and is fundamental to the structural and functional properties of all cells in our body. Our muscles are made of protein and some of our most important anabolic hormones are made of protein including insulin and growth hormone. Proteins are involved with the metabolism of energy and nutrients in our body. In terms of sport, protein is the primary essential nutrient capable of building new muscle and repairing damaged muscle.

Along with Carbohydrates and Fats, Protein is one of the three primary macronutrients required for the normal day to day functioning of the body. Protein requirements are not the same for everyone and vary according to many factors like age and activity. So how much protein should you be eating?

Protein Requirements for Adults

The International Society of Sports Nutrition recommends the consumption of 0.8g protein/kg bodyweight for a sedentary adult. This is the bare minimum someone who is not exercising should be consuming to maintain muscle mass. This equates to 64g of protein per day for an 80kg person.

According to the same guidelines, an adult who is regularly involved in recreational exercise, for example, a low impact team sport or regular walking, should up this to 1.0-1.4g protein/kg bodyweight per day.

Protein Requirements for Men

If you are not working out, a general goal to aim for is obtaining 20% of your daily energy from protein. Because men have a higher calorie requirement than women, this means they have to eat more protein on a gram by gram basis.

There are however a number of exceptions to the above guidelines, and eating a high protein diet has a number of benefits.

If a man is involved in any sort of training or exercise, he needs to up his protein intake to ensure muscle mass is not lost. Like skin or bones, the cells that make up muscles are not static. Old muscle is continually broken down and lost, and new muscle is laid down to replace it. Doing any sort of exercise enhances this cycle, and also stimulates the body to lay down greater amounts of muscle (2). This means that the body must have additional protein to replace and build upon the muscle that was broken down as a result of exercise.

The International Society of Sports Nutrition recommends upping the intake to 1.2-1.4g protein/kg bodyweight for men involved in endurance sports, 1.2-1.8g protein/kg bodyweight per day for men who are doing high intensity, intermittent exercise, and 1.4-2.0g for men involved in weight restricted exercise (1). A higher protein intake can, in the long term, increase the basal metabolic rate, due to the heightened energy demands of muscle tissue, and in the short term it promotes feelings of satiety that assist in appetite control.

Protein Requirements for Muscle Growth

Putting down muscle requires a lot more protein that just maintaining the muscle that you have. It is recommended that people actively gaining muscle eat between 1.4 and 1.8g protein/kg bodyweight per day (1). It should be noted that people using anabolic hormones like testosterone, insulin or growth hormone may need a higher level of protein to maximise their results.

Generally, people trying to lay down muscle will use protein at a higher level, up to 3g protein/kg bodyweight per day, but 2g/kg is probably the average.

Research has shown there is an upper limit to the amount of protein that can be safely ingested per day. When amino acids are broken down, ammonia is produced as a by-product. It is theoretically possible to produce ammonia, which is toxic, at a higher rate than the body can excrete it. A group of researchers studied the rate of urea formation and the daily protein requirements and determined that the upper safe limit of protein consumption was just over 3.5g protein/kg bodyweight per day (3).

Protein Requirements for Bodybuilders

The protein requirements for gaining muscle apply to bodybuilders and 2g protein/kg bodyweight per day is a good amount to aim for. Bodybuilders taking a break from training, or looking to maintain their physique can afford to eat a little less protein – the recommended intake for maintenance is 1.2-1.4g protein/kg bodyweight/day. This is higher than the amount recommended for a sedentary individual, as somebody with more muscle tissue, like a bodybuilder, has more to maintain and requires more protein to do so.

While the body is able to tolerate large amounts of protein, there is a maximum rate at which the body can absorb it. Maximising the absorption of protein is of concern to people who have a large daily intake, like bodybuilders and those who are building muscle.

The rate at which protein is taken into the body varies by type. Fast acting proteins like Whey Protein Isolate can be taken up by the body at a rate of 8-10g per hour, whereas cooked egg is absorbed into the body at a rate of less than 3g per hour. This places a theoretical maximum on the amount of protein that can be absorbed in a day (4).

Consuming a mix of fast and slow digesting proteins will ensure that the body has sufficient amino acids to build muscle all day. Another tip to maximise protein intake is to eat small, frequent, protein rich meals.

(1) Antonio J, Kalman D, Stout JR, Greenwood M, Willougby DS, Haff GG. 'Essentials of Sports Nutrition and Supplements'. International Society of Sports Nutrition. Humana Press 2008
(2) Pasiakos SM. Exercise and amino acid anabolic cell signaling and the regulation of skeletal muscle mass. Nutrients. 2012 Jul;4(7):740-58.
(3) Bilsborough S & Mann N. 'A Review of Issues of Dietary Protein Intake in Humans.' International Journal of Sport Nutrition and Exercise Metabolism, 2006, 16:129-152
(4) Dangin, M., Y. Boirie, C. Garcia-Rodenas, P. Gachon, J. Fauquant, P. Callier, O. Ballevre,and B. Beaufrere. 'The digestion rate of protein is an independent regulating factor of postprandial protein retention.' Am. J. Physiol. Endcrinol. Metab. 280: E340-E348, 2001.

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