Protein is one of our three macronutrients that are essential to our diet, the other two are fat and carbohydrate. Protein, like carbs, provides 4 calories per gram. Every bit of protein we eat, or that exists in our body is made up of amino acids. There are 20 amino acids that join together in various numbers and sequences to make up the proteins that form muscle, hormones, enzymes, DNA and antibodies. There is a constant turnover between our stores of protein, our free amino acids, the protein that we take in and the protein that we excrete.
Clearly protein is important for all the bits in our body named above. An average person needs about 0.8g/kg/day of protein, or roughly 15% of their total diet to be protein to account for the daily turnover. We are rarely deficient in this however. Athletes may need a little more for their goals and demands of exercise. Weight loss goals may also benefit from higher intakes of protein. Seldom are these levels higher than 1.5g/kg/day though. The main challenge with protein intake is not in getting enough, but rather getting the right type and at the right time.
We get our protein from both animal and plant sources. They are different in their amino acid profiles. Only animal sources gives us “complete” proteins because all 9 essential amino acids are in them. This is our milk, eggs, meat, poultry, fish. Plant sources of protein (maize, legumes, nuts etc) are “incomplete” because they lack one or more essential amino acid. This means they cannot cause growth and can lead to malnutrition if not eaten in combination with other protein sources. Vegetarians need to combine their sources of protein to make sure they get all 9 essential amino acids.
The different sources of protein provide different quality of protein, this is their biological value. A higher value means greater availability of protein and the greater percentage we can actually use. The best sources here are whey, egg and milk. Next comes beef, poultry and fish. Lower down are soy and casein.
Timing of our intake is also important. Protein intake before and after exercise significantly improves lean mass and strength gains and also improves recovery. Aim to include about 20g of protein at these times with a source of carbohydrate. (See my documents page for a list of foods and their respective protein content). Endurance and ultra endurance athletes should consider consuming protein during exercise to prevent lean mass losses and assist recovery between sessions.
Concerns over very high protein intakes (+- 3g/kg/day, 80% total energy) exist for risks of cardiovascular disease, kidney dysfunction, calcium losses and dehydration. Mostly these claims are unfounded provided the intake is from food sources predominantly (i.e. not concentrated or isolated supplements). The concern for dehydration is warranted and those on high protein diets do need to take note of their hydration status, weigh themselves regularly and drink sufficient liquids.