Proteins are everywhere in our bodies.
When you take a look at yourself in the mirror virtually everything that you see - your hair and skin for example - is made up of protein. And underneath the surface it is the same: muscles, bones, all tissues, blood, antibodies, enzymes and all body organs.
In fact, protein makes up about 75% of the body after water has been excluded.
As it turns out protein is fundamental to our very existence.
Proteins are made up of building blocks called amino acids.
There are 22 amino acids, 9 of which are considered to be ‘essential’. This means that our bodies are unable to synthesise them so they have to be obtained, preformed, in our diet (10 are essential in children).
Under the control of DNA, our body uses amino acids circulating in the bloodstream to make protein. These amino acids come from dietary proteins and also from the breakdown of tissues.
The amino acids can be thought of as the alphabet from which many thousands of different proteins are constructed.
Just as with words, where having letters missing prevents us from proper communication, so with proteins: when some amino acids are not available in the correct quantity, proteins cannot be made.
Since there are tens of thousands of proteins being made on a regular basis within our bodies, the effects of a shortage of the building blocks can be devastating.
Surprisingly, despite its pivotal role in our bodies, not very much is known about protein and health.
It is known that amino acids are not stored, and so protein is needed daily for the synthesis of new proteins for building and repairing tissue.
It is also known that getting too little protein on an ongoing basis results in serious health problems – loss of muscle mass, failure to thrive, poor mental development, low immunity, heart and respiratory failure and, if it continues for long enough, death.
The current recommendation is that adults should eat a minimum of 0.8 grams of protein for every kilogram of body weight per day to keep from slowly breaking down their own tissues.
Another simple way to get a rough estimate of the mass of protein that should be eaten daily is as follows: body weight (pounds) x 0.4 or body weight (kg) x 0.9
This means that 10% - 35% of your calories should come from protein.
Fortunately, for some people – especially those in affluent countries - getting enough protein is not a problem – in fact, getting too much might be more of an issue. However, there are many millions of people around the world facing protein starvation as a way of life.
Excess protein leads to several health problems:
* increased stress on the kidneys, leading to dehydration and eventually malfunction of the kidney’s filtration system.
* Osteoporosis. Excess amino acids are converted into organic acids. The kidneys deal with these acids by pushing more calcium into the urine. This calcium comes from the bones, so the bones become less dense over time, and osteoporosis is likely to develop.
* Cancer. Recent studies suggest that a low protein diet may protect us from certain types of cancer especially breast, prostate and colon cancers. This is thought to be due to a lowering of the production of a plasma growth factor (IGF-1), high levels of which have been associated with increased risk of these cancers.
The protein needs to contain all the essential amino acids in a proper balanced ratio to be effective – known as complete protein.
This means that the source of dietary protein must be suitable. Eggs contain complete protein, and other animal products are also good sources of complete protein.
Unfortunately, these proteins come along with large amounts of fat and little fibre!
On the other hand, vegetables, fruits and nuts tend to contain incomplete proteins, so food balancing must be done with care when these are the main source of protein.
For example, rice is short of certain essential amino acids which are found in greater amounts in dry beans and vice versa. Therefore, combining these two foods would supply the full complement of amino acids that the body needs to function well.
Interestingly, if one looks at traditional diets this kind of mixing has always taken place – learned from experience over the centuries before science was available to explain why!
A mixed diet is obviously the best way to ensure that all one’s protein requirements are met on a daily basis.
Common proteins are:
* Enzymes e.g. amylase needed for digesting starch
* Structural proteins e.g. collagen in connective tissue
* Transport proteins e.g. haemoglobin which transports oxygen in the blood
* Protective proteins e.g. antibodies which fight against foreign bodies
* Contractile proteins e.g. actin and myosin muscles
* Storage proteins e.g. myoglobin which stores oxygen in muscles
* Regulatory proteins e.g. growth hormone and insulin
* Macromolecular complexes e.g. the cytoskeleton which forms a framework within cells
In summary, why is good balanced protein important for a healthy diet?
The following critical functions are entirely dependent on an adequate supply of protein, especially the essential amino acids.
* Growth and development
* Tissue repair, maintenance and regeneration throughout life
* Immune function
* Hormonal balance
* Effective metabolism since it is dependant upon enzymes which are made primarily of protein
* As an energy source in the absence of sufficient carbohydrate.
If you have any doubts about your protein intake, supplementation with a good protein drink might be advisable.
To see how protein fits into the ideal food pyramid, click on our Nutrition and Food page.