Articles – A Bit on Protein

What is it ?

Proteins are polymer chains of amino acids linked together by peptide bonds. Protein is a nutrient needed by the human body forgrowth, repair, metabolism, immunity, digestion, nerve function, hormonal function, basically every cell, tissue and physiological process in the body requires protein to function. There are 20 (plus a few more, but not important for now) individual amino acids which are divided up between essential and non-essential amino acids.

Table 1: List of essential and non-essential amino acids

Essential Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Trytophan, Valine
Non- Essential Alanine, Asparagine, Aspartic Acid, Cysteine, Glutamic Acid, Glutamine, Glycine, Proline, Serine, Tyrosine, Arginine, Histidine

The essential amino acids cannot be made in the body while the non-essential one’s can. To form a protein, whether it’s an enzyme or muscle fibre, all 20 amino acids are required.  Therefore, it is necessary to consume protein foods that contain all the essential amino acids.

What does it do ?

Protein is present in almost every cell, tissue and organ of our body. Apart from water, it is the most abundant nutrient in the body. Here are just some of its functions:

  • Required for building and repair of body tissues (muscle, organs,)
  • Enzymes, hormones, and many immune molecules are proteins
  • Essential body processes such as water balancing, nutrient transport, and muscle contractions require protein to function.
  • Protein is a source of energy.
  • Protein helps keep skin, hair, and nails healthy.
  • Protein, like most other essential nutrients, is absolutely crucial for overall good health.

In terms of fitness and how it relates to athletic performance, here’s what protein does

–       Produces and repairs muscle which is needed for speed/strength/power and endurance

–       Produces metabolic enzymes which are needed to produce ATP (i.e. energy)

–       Forms haemoglobin which is needed to transport oxygen to the cells to produce energy

–       Needed to build blood vessels and capillaries which supply muscle

–       Needed to build mitochondria, the engine rooms of the muscle where ATP is produced

–       Needed to anabolic hormones which stimulate protein synthesis muscle growth

So, if you want to get fitter, whether it’s to build muscle or improve aerobic fitness, you need protein.

Sources of Protein

There are several factors that need to be considered when deciding on “good” protein sources. Specifically, factors such as protein content, digestibility, amino acid profile and nutrient content have to be considered. Someone might tell you “beef” is a good protein source while others will tell you “beans” are. But is there a difference ?? of course there is, and the difference is found in the factors that I just mentioned. Let’s have a little look

Protein Content

A simple way to assess the protein source of a food is to look at the grammes of protein provided per 100g. For example

Table 2: Protein content per 100g

Food Protein per 100g
Beef 35g
Baked Beans 10g

So as you can see, eating the same amount of beef steak as baked beans will give you around 3 times the amount of protein. But this is just one thing to consider

Amino Acid Profile

We have 8 essential amino acids that the body cannot manufacture, so we have to obtain them from food.  Animal foods contain all of the essential amino acids – meats, fish, diary, eggs. This are termed “complete” protein foods as they contain all 20 amino acids. Plant foods such as vegetables, legumes, beans, nuts and grains do not contain all essential amino acids and are therefore termed “incomplete”.  However, the full set of essential amino acids can be obtained from plant foods simply by combining food intake e.g. rice + beans.  Animal sources of protein are  higher in specific amino acid content such as branched chain amino acids (BCAA’s). These amino acids have been shown to be important for athletes due to the role they play in protein synthesis  (1).


When you eat a protein food, it is first digested in the stomach by acid and enzymes. It then gets released into the small intestine where more enzymes (proteases) are released to break the food down into amino acids. These are then absorbed into the bloodstream and sent to the liver and muscle. However, if you eat 100g of protein, not 100g of protein gets into the bloodstream. The way of measuring this is called “Biological Value”. This is as measure of how much of the protein in the food actually gets digested and used. The table below shows:

Table 3: Biological Value of Protein Foods

Food Source Protein Digestibility (%)
Egg 97
Milk and Cheese 97
Peanut Butter 95
Meat and Fish 94
Whole Wheat 86
Oatmeal 86
Soybeans 78
Rice 76

As you can see, animal proteins have the highest BV. If you eat 100g of egg protein, you will get approximately 97g of protein into the bloodstream. If you eat 100g of rice protein, you will get 76g of protein absorbed. Therefore, you need to eat more amounts of plant foods to get equivalent amounts of protein into the system compared to animal foods. While the BV can be used as an indication of the protein absorption, it is now considered a bit outdated. There are a few flaws with this measure and a new method (Protein Digestibility Corrected Amino Acid Score – PDCAA) is now more recognised. However, the list in general remains the same in terms of priority – diary, eggs, meats and fish provide more digested protein per weight than grains, legumes and beans.

Nutrient Content

When choosing what type of protein food to eat, it is also important to consider what else you are getting. The first thing is macronutrient content i.e. carbohydrate and fat. Beef, Beans, Chicken and Nuts all contain protein. However, their carbohydrate and fat contents differ as illustrated in table 4 below:

Table 4: Macronutrient breakdown of Protein foods per 100g

Food Protein (g) Carbs (g) Fat (g)
Beef 30 2 20
Beans 10 20 0.5
Chicken 25 0 1
Nuts 25 10 50

Thus, you can eat a certain food, which provides protein, but your carbohydrate and fat intake could be very different.  The type of food you choose to eat will depend on several other factors like personal goals (i.e. weight loss or weight gain), timing, overall daily calorie requirements, and macronutrient daily targets. For example, a post training meal should typically consist of high protein and minimal fat. Therefore, a chicken fillet with this meal would be a better choice than 100g of nuts. However, a mid afternoon snack on a rest day could be nuts, where carbohydrate intake can be relatively low and fat intake can be relatively high.

Aside from the macronutrient content, the micronutrient content must also be taken into account. Protein from plant sources will come with fibre, certain B vitamins and minerals like magnesium. Protein from animal sources contains Iron (heme-type), Zinc, Vitamin B12 and fat-soluble vitamins such as Vitamin A and E. Red meats supply other nutrients such as creatine and CLA (conjugated linoleic acid) which are important for growth and lean muscle mass. Protein from fish will come with omega-3 fatty acids which have been shown to improve body composition and reduce inflammation. Dairy proteins contain immunoglobins shown to improve immune function.

The source of the food dictates its health and YOUR health

Processed factory farmed mince meat is nutritionally very different to your grass-fed pasture raised meat you get from your local butcher. The same can be said about milk, yoghurts, chicken and eggs. Below is an overview of the nutritional benefits of choosing grass-fed pasture raised animal products over factory farmed grain fed types:


  • Meat from grass-fed animals has two to four times more omega-3 fatty acids than meat from grain- fed animals.
  • When chickens are housed indoors and deprived of greens, their meat and eggs also become artificially low in omega-3s.
  • Eggs from pastured hens can contain as much as 19 times more omega-3s than eggs from factory hens.
  • When ruminants are raised on fresh pasture alone, their products contain from three to five times more CLA than products from animals fed conventional diets. CLA is a fatty acid that has recently been studied as a potent cancer fighter.
  • The meat from the pastured cattle is four times higher in vitamin E than the meat from the feedlot cattle and, interestingly, almost twice as high as the meat from the feedlot cattle given vitamin E supplements.


  • Milk from a pastured cow can have five times as much CLA as a grainfed animal.
  • Milk from pastured cows also contains an ideal ratio of essential fatty acids or EFAs. Studies suggest that if your diet contains roughly equal amounts of these two fats, you will have a lower risk of cancer, cardiovascular disease, autoimmune disorders, allergies, obesity, diabetes, dementia, and various other mental disorders.
  • When a cow is raised on pasture, her milk has an ideal ratio of omega-6 to omega-3 fatty acids. Replace two-thirds of the pasture with a grain-based diet and the milk will have more than five times the amount of omega-6 fatty acids than omega-3s, a ratio that has been linked with an increased risk of a wide variety of conditions, including obesity, diabetes, depression, and cancer.
  • Grassfed milk is higher in beta-carotene, vitamin A, and vitamin E. This vitamin bonus comes, in part, from the fact that fresh pasture has more of these nutrients than grain or hay. These extra helpings of vitamins are then transferred to the cow’s milk.

Free-range (pastured) eggs

  • When compared to commercially raised, supermarket eggs, free-range eggs have:
    2/3 more vitamin A
  • 7 times more beta carotene
  • Up to 19 times more omega-3 fatty acids
  • Significantly more folic acid and vitamin B


How much so you need ?

That depends again on several factors – age, weight, sex, sport type and individual goals. The general recommendation for athletes is 1.5 – 2.0g/Kg. However, there have been studies to show that higher intakes (2.0 – 3.0g/Kg) can be beneficial to certain athletes (4). If you take an average male weighing 75kg, football/GAA player, looking to increase lean muscle mass. Then

75Kg Player Protein Requirements Total Foods = 150g Protein
75 x 2g = 150g protein per day -1 large chicken breast-1 serving whey- 3xeggs

– 1 large steak or mince.


–       Protein has several important functions to perform other than building muscle

–       Protein is vital for fitness and performance gains

–       Animal sources have a higher biological value than plant sources

–       Fat/Carbohydrate quantities differ depending on the Protein food type

–       Choosing what type of protein food depends on timing and individual goals

–       Animal sources are more nutrient dense than plant sources

–       Choose your animal foods from grass-fed, pasture raised/free-range sources

–       Athlete protein requirements are 1.5 – 2.0g/Kg


  1. Kimball S.R and Jefferson L.S. Signaling Pathways and Molecular Mechanisms through which Branched-Chain Amino Acids Mediate Translational Control of Protein Synthesis. J.Nutr, 136:2275 – 2315, Jan 2006.
  2. McAfee AJ et al. Red Meat Consumption: An overview of the risks and benefits. Meat Science, Vol 84 (1) 1 – 13, Jan 2010.
  3. Calder PC. Omega-3 Polyunsaturated fatty acids and human health outcomes. Biofactors. 2009.
  4. Tipton K.D and Wolfe R.R. Protein and Amino Acids for Athletes. Journal of Sports Sciences, 22, 65 – 60, 2004.