The Macronutrients: Protein

The Macronutrients: Protein

Following on from last weeks article on carbohydrate, this week I will focus on another of the Meat, fish, eggsmacronutrients, protein.

Approximately 20% of an adult’s (non fat) bodyweight is comprised of protein, with the majority of it located in structural tissue such as muscle, skin, connective tissue and bone. Essential for growth and repair, proteins have many functions in addition to their structural role in the body.


Functions of Protein

  • All enzymes are proteins. These enzymes are essential for the various chemical processes on which body function depends.
  • Proteins act as transporters in blood and body fluids for many molecules for example, haemoglobin in red blood cells is a protein responsible for transporting oxygen.
  • Some hormones such as insulin are proteins
  • Our immune system’s antibodies are proteins


Biological Value and Amino Acid Content

Just as carbohydrate has a simple form in glucose, the building blocks of protein are called amino acids. There are 20 amino acids, some of which can be produced in the body. Of the 20, there are 8 that the body cannot synthesise (10 in children and some older adults) therefore we must get these externally from the diet.

The biological value of a protein is related to ease of digestion and amino acid content. Higher biological value proteins come from foods containing all of the amino acids (including the essential) in the sufficient quantities. If one or more of the essential amino acids are not present in a protein, it is said to have a low biological value. Lower value protein diets (even if they contain adequate energy) may eventually lead to protein malnutrition.

Higher value proteins are derived from animal sources e.g. meat, eggs, milk, dairy products and fish. Proteins from plant sources may not contain all the essential amino acids and the specific amino acid content will differ in each type of plant.

It is for this reason that vegans who do not have a varied diet can have a greater risk of protein malnutrition than those individuals who eat meat. However nutritional diversity is key here. By consuming a diet that contains a wide variety of different types of plants, it is possible to provide all essential amino acids by combining them from different plant sources.

No physiological advantage exists from an amino acid derived from an animal compared with the same amino acid from a vegetable origin. Well-balanced vegan and vegetarian diets are correlated with reduced body weight and lower incidence of certain chronic diseases.


Daily Requirements

Recent studies conclude that sedentary adults require no more than 0.83g per kg per day to satisfy their protein needs. For a 70kg individual this would equate to 58.1g of protein per day. This is easily achieved given that 100g of chicken breast contains approximately 33g of protein, a small 100g tin of tuna contains 19g of protein or a single egg contains around 7g.Protein from nuts

The recommended intake for athletes varies, but generally ranges from 1.2 – 1.8 g per kg of bodyweight per day to achieve optimum adaptation and repair from training stimulus. However, according to the International Society of Sports Nutrition, athletes engaging in higher volume training such as strength training may well benefit from slightly higher intakes ranging from 1.5 – 2.0g per kg of bodyweight per day. The consensus is that there would seem to be no benefit from consuming excessive protein above these recommended levels.



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Liam Leech, BSc (Hons) Sport and Exercise Science, MSc. ANutr.

Liam Leech

BSc (Hons) Sport and Exercise Science, MSc. ANutr.






Replies for “The Macronutrients: Protein”

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