ProteinProtein is essential, and human life cannot exist without it. An adequate intake is required in order to grow and maintain the body. The amino acids from protein intake form the building blocks that are required for many thousands of body substances, from hormones to skin to the lining of the digestive tract.
Processing protein
Hydrochloric acid in the stomach activates pepsinogen; the active form of this, pepsin, begins the digestion of proteins in the stomach by breaking the peptide bonds. A group of enzymes called proteases, released by the pancreas into the small intestine, complete the breakdown of peptides and polypeptides into individual amino acids.
The amino acids are absorbed into the bloodstream from the small intestine, where they are transported to the liver and then into general circulation via the portal vein, where they form a small general pool of amino acids. These are then available to whichever cells in the body require them for repair, hormone synthesization etc.
Excess amino acids cannot be stored by the body and are deaminated. The nitrogenous part (ammonia) is converted into urea in the liver for excretion in urine, and the remainder is converted into glucose or Acetyl-Co-A and used for energy, or stored as fat if in excess of requirements.
A deficiency in magnesium and several other important nutrients can result in the conversation of ammonia to urea being inefficient. This build up of ammonia can affect the Krebs cycle, in which glucose is turned into energy. This will leave the person feeling weak and fatigued, often involving symptoms such as headaches, lethargy, irritability and poor tolerance of high protein foods.
Protein and allergy
In the majority of cases food intolerances are the result of partially digested proteins being absorbed into the blood stream and causing an immune response. This can happen as a result of inadequate HCI or protease levels to sufficiently break the protein down. In situations of 'leaky gut' where the villi of the intestinal walls have become further apart, they allow larger particles of food to pass through.
Protein deficiency
Severe protein deficiency is called kwashiorkor. This is normally only seen in developing countries where there is severe food shortage.
The characteristics of this condition are swollen ankles (odema) and a distended abdomen (ascites) which disguise the malnutrition. Growth will be retarted, there is severe liver damage, hair loss, listlessness, apathy and irritability.
Not all proteins are created equal
Proteins are made up of smaller units called amino acids. There are 10 amino acids that are referred to as 'essential'; all amino acids are essential, however this group are given the title as they must be obtained through dietary sources, whereas the others can be manufactured within the body, given the correct conditions.
Essential Amino Acids
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
Non-Essential Amino Acids
Alanine
Arginine (An EAA during infancy when demand will outstrip synthesized supply)
Asparagine
Aspartic Acid
Cysteine
Cystine
Glutamine
Glutamic Acid
Glycine
Proline
Serine
Taurine
Tyrosine
In some people the genetic pathways do not exist for the synthesization of NEAAs (Non Essential Amino Acids) to take place correctly, also due to genetics again one persons requirement for a certain nutrient may be vastly different to that of another. This can result in a particular NEAA becoming essential for that particular individual.
In his book, Amino Acids in Therapy, Leon Chaitow discusses various situations where ones requirement for any nutrient, not just amino acids, can be increased over and above that usually supplied by the diet. These situations include stress factors, exercise levels, trauma, shock, surgery, and intake of toxic substances, either environmental or dietary.
The amino acids commonly involved in these situations are generally known as conditionally essential, and are shown in italics above.
This table covers the basic amino acids, however there are many others mentioned in other texts, and new amino acids are being discovered and researched all the time.
Amino acids can occur in two isomer forms, D & L. The L form is that found in nature and is recognised by the body. The synthetic form, D, cannot be utilized by the body. The exception to this rule is with phenylalanine, where a combination of the D & L forms have proved to be an effective painkiller.
Recommended intakes
RNI figures are based on the level of a nutrient that would be suitable for 97% of the population. The figures for protein are as follows:
Reference Nutrient Intakes for Protein, g/day.
Age RNI . Age RNI
0 to 3 months 12.5g . Men 11 to 14 yrs 42.1g
4 to 6 months 12.7g . Men 15 to 18 yrs 55.2g
7 to 9 months 13.7g . Men 19 to 49 yrs 55.5g
10 to 12 months 14.9g . Men 50 + yrs 53.3g
1 to 3 yrs 14.5g . Women 11 to 14 yrs 41.2g
4 to 6 yrs 19.7g . Women 15 to 18 yrs 45.4g
7 to 10 yrs 28.3g . Women 19 to 49 yrs 45.0g
- - . Women 50 + yrs 46.5g
Pregnant women 51.0g .
Breast feeding women 53 to 56g
Vegetarians and Vegans
Protein quality is calculated by reference to the egg, which is seen as the perfect source. Many animal products are referred to as complete proteins as they contain all of the essential amino acids, whereas plant based foods will often lack one or more. This is not the case with soya which is equal to animal products in containing all amino acids.
Previously it had been thought that vegans/vegetarians should practice food combining to ensure that all the amino acids were present in one meal. However, research has shown that this is not necessary as long as a variety of foods is eaten, as the amino acids are present in the body for up to 48 hours before being used and so have the opportunity to be combined.
Sources of protein
Vegetarian sources of proteins include:
Good sources
Chick peas (200g or 7oz) 16.0g
Baked beans (225g or 8oz) 11.5g
Tofu (140g or 5oz) 10.3g
Cow's milk (½ pint) 9.2g
Lentils (120g or 4¼oz) 9.1g
Soya milk (½ pint) 8.2g
Muesli (60g or 2¼oz) 7.7g
Egg, boiled 7.5g
Peanuts (30g or 1oz) 7.3g
Bread, (2 slices) 7.0g
Hard cheese (30g or 1oz) 6.8g
[Table referenced from the Vegetarian Society]
Other sources of high proteins are:
[Table referenced from The Worlds Healthiest Foods]
Protein in dieting
Protein can be used by the body to provide energy, however the body will only do this in extreme circumstances, i.e. starvation (or at least what the body believes to be starvation, an example being extreme anorexia). Protein is acidic in the body, and high protein diets, as are currently popular, can create an acid imbalance in the body. Ultimately this can lead to some serious health consequences, such as osteoporosis. The body takes calcium from the bones to put back into the blood stream to try and combat the acidity leading to a gradual weakening of the bones.
Protein and carbohydrates both contain 4 calories per gram, whereas fat contains 9 calories per gram.
In conclusion
Protein is as essential in our diet as carbohydrates and fats; each have their own role to play in the human body. It is essential to ensure that you are receiving a good balance of all the essential amino acids, but that the ratio of protein in your diet is relevant to that of the other macronutrients. Protein is useful in balancing blood sugar so should always form a part of any meal or snack that you have. It is also important to ensure that your body can deal with the protein it is receiving by ensuring that you have adequate HCI, enzyme and micronutrient levels. High protein diets are not a recommended way to lose weight, as sustaining them lifelong can cause many health implications, and a sensible balanced diet, along with regular exercise can have the same effect, and once you get into the habit, easily sustained!
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