Proteins are made up of basic units called AMINO ACIDS. Around 25 amino acids exist in nature and of these, 8 are deemed ESSENTIAL. They are ESSENTIAL as the body cannot make these and they have to be supplied in our diet.

Proteins are long chains of amino acids all linked firmly together and usually wrapped in on themselves to form a tangled ball.

When the body needs to synthesis a new protein it looks around for the right amount of each of the component amin acids.

One major source is old proteins that are no longer in use. These are simply recycled to make new ones. When a semi-essential or non-essential amino acid is in short supply the cell will simply make what it needs, but when an essential amino acid is missing, the protein will not be able to be made up until that amino acid is supplied via the food we eat.

Biological Value (BV) is the proportion of absorbed protein retained in the body. A protein that is completely useable e.g. an egg or human milk has a BV = 90-100%, meat and fish has a BV = 75-80%; wheat protein has a BV = 50%.

Incomplete Protein: Low Biological Value (LBV)

This means that the protein is missing at least one essential amino acid. Plant products in our diet provide incomplete protein, apart from soy-bean.

Vegetarians need to combine foods to ensure quality (complete protein) of intake and also ensure sufficient quality is consumed. Because most plant proteins are incomplete, vegetarians and vegans need to combine different protein food to ensure they consume all the essential amino acids. Whatever amin acid is missing from one protein food will be provided by another protein food.

Animal proteins offer a very concentrated source of protein in our diet, making it easy to consume enough protein.

Plants do not offer such a concentrated supply so more needs to be eaten to ensure sufficient protein is consumed.

Lacto (will eat dairy products) or lacto-ovo (will eat dairy products and eggs) vegetarians will find it much easier to consume sufficient protein than vegans who eat no animal products whatsoever.

Soy bean is deemed a complete protein.

It is clear then that although we need to eat protein on a daily basis to keep our cells topped up with all the amino acids, we in fact need to pay particular attention to the source of the protein we eat.

Food Sources of Protein: Oily fish, Omega 6 and Omega 3, yoghurt, soymilk, cheese, tuna, sardines, all kinds of beans, grains, legumes, vegetables, nuts and seeds, chicken and meat.

Protein Combination Image

Amino Acids are vital for growth and the repair and maintenance of body tissue; this is their structural role.

Additionally amino acids have a biochemical role in that they are the basis of many hormones, enzymes, anti-bodies, neuro-transmitter and carriers of oxygen, fats and other substances within the blood.

• All enzymes are proteins. Enzymes control both the rate and the pattern of all the chemical reactions that take place in the body including the digestion and extraction of energy from foods.
• Some hormones are proteins. These are chemical messengers that set normal patterns of responses within the body and help regulate a wide range of functions. For example: insulin is a hormone that controls blood glucose (sugar) levels.
• Antibodies are proteins. These are produced by white blood cells and fed directly into the bloodstream to fight infection, and disease.
• Protein can be used for energy if glycogen is in short supply.

How Much Protein?

As with fats, both the quality and quantity of protein is of paramount importance.

Protein needs per day = 0.80g per kg of body weight per day.

Using this formula as a guideline lets us work out the protein needs of a person weighing around 60kg.

More detail on conversions between different measurements can be found in the appendices.

Guidelines from the Food Standards Agency recommend that 10 – 15% of total calorie intake per day should come from protein.

Using the above formula to try and work out your own protein needs.

If you do not know your weight in kilograms work out your weight in pounds and divide by 2.2 to convert to kgs. (See conversions appendices at the back of the manual).

This requirement applies to people who maintain a desirable body weight and composition. Individuals who are considerably bigger than this with a relatively high amount of body fat need to work out their needs based on their desirable weight as research has shown that fat tissue has a lower rate of protein synthesis than lean tissue.

Because of this, strength training athletes who have a large amount of muscle mass and a low percentage of body fat may have higher requirements. The consensus from research studies have estimated this to be approximately 1.4 – 1.8 per kg body weight.

HEALTH RISKS ASSOCIATED WITH HIGH PROTEIN INTAKE

Although protein is needed for many vitamin functions within the body, it is not often used for energy production. It can be very easily utilised for this purpose, even in working muscles, but as long as there are sufficient carbohydrate stores available protein will not be used. Add to this that protein turnover within the body is continual, and that there is usually a large pool of amino acids available for protein synthesis, and you can see that dietary protein needs on a daily basis are quite small. Interestingly, the protein needs of slim, lean endurance runners may well be greater than the needs of strength trainers as they will use a significant amount of protein as energy for muscular contraction, and a higher intake may help to spare their own body protein. There are many misconceptions about protein in the diet, e.g. more is better, or a high protein diet is essential for muscle building.

Furthermore, if protein is eaten in excess of body requirement, it cannot be stored by the body in this form (apart from a minute pool of amino acids in each body cell) and has to be converted to carbohydrate or fat. Excess protein stored as fat will enhance the risk of obesity. This process is carried out by the liver and requires the removal of nitrogenous material that would otherwise become toxic to the system. In such circumstance the liver and the kidneys are put under stress by having to work hard to remove these waste products. What is left of the amino acid.at this stage is a carbohydrate like skeleton, which in normal circumstances is metabolised to produce energy. If this energy is not used it is converted to fat for storage; consequently, excess protein can cause body fat to build up and can lead to obesity.

A high protein intake can lead to the accumulation of ammonia in the blood (which is toxic, particularly to :–­ brain cells) and more seriously a condition called hyperammonaemia, which is excess ammonia in the urine. The nitrogen part of the amino acid must be removed (a process called deamination) and the resulting carbon skeleton converted to glucose. This may be used either as an immediate energy source or stored as glycogen or triglyceride by either the liver or other tissues, such as muscle. The nitrogen waste produced following deamination must not be allowed to accumulate in the body due to its toxicity. So it is converted to urea and excreted from the body by the kidneys. Therefore excess protein places extra pressure on the kidneys and as this process also necessitates the excretion of water, the consumption of excessive amounts of protein may also compromise fluid balance.

Meat is an extremely concentrated source of protein, and if eaten several times a day over a period of several days can generate a state of acidity within the body, which then has to be neutralized; the body has to release calcium and other mineral salts from the skeleton to buffer this excess acidity. When blood reserves are used up, the body calls on calcium from the bones. We can see the link then between excessive protein consumption and bone density loss, consequently resulting in an insufficient uptake of some vitamins and minerals (e.g. calcium). Moreover calcium may be “dumped” in inappropriate places such as the arteries and the joints giving rise to cardiovascular disease and arthritis.

Excessive dietary protein can be harmful because the breakdown of large quantities of this nutrient produces undesirable quantities of urea and other compounds that may strain the liver and the kidneys. The Atkins diet and other such high protein diets work on the theory that a high protein and low carbohydrate diet evokes low insulin levels which will cause dietary ketosis, where fat is not taken into fat cells but released and the by products of fat breakdown (ketones) provide the fuel for daily functioning.

Therefore by eating fewer carbohydrates the body will begin to produce less insulin. With fewer carbohydrates to burn for fuel, the body turns to other energy sources, e.g. the fatty acids circulating in the blood and the ketone bodies produced by the liver.

KETONES AS FUEL

Under conditions of carbohydrate starvation, such as during fasting, prolonged exercise, and diabetes, ketones can be used as fuels. During this process the liver catabolizes fat to acetyl-CoA, and then converts acetyl-CoA to ketones. The ketones then circulate and can enter cells such as muscle, nerves and brain. In particular, during dietary starvation the ability to sustain life depends on the ability to form and utilize ketones. Within a day of fasting, the liver’s glycogen supply is exhausted in the attempt to maintain blood glucose level. The brain, and to some extent the kidney’s, depend heavily on glucose as fuel. Entry of fatty acids into the brain is very limited, thus in the first few days of starvation, skeletal muscle is catabolised rapidly to provide material for glucose synthesis. This rapid loss of lean tissue cannot be maintained for very long without severely affecting the individual. During untreated diabetes, blood glucose levels can be extremely h’igh, but the muscle cells can be starving for glucose. Glucose cannot enter the muscle cells without insulin, which, due to diabetes is lacking. Very high levels of ketones result, which frequently constitutes another problem as ketones are acidic and can affect an individual’s physiology and biochemistry.

HOW?

Carbohydrate serves as a primer for fat metabolism. Certain products from carbohydrate breakdown must be available for the metabolism of fat. If carbohydrate metabolism is insufficient the body will need to metabolise a greater amount of fat than it CAN metabolise. The result is an incomplete fat breakdown and the accumulation of acetone-like by products called KETONE BODIES. This situation may lead to a harmful increase in the activity of body fluids; a condition called acidosis, or more specifically related to fat breakdown as KETOACIOOSIS (ketoacidosis is characterized by the accumulation of large amounts of acetoacetic acid). If ketosis persists the acid quality of the body fluids can increase to potentially toxic levels, such as diabetic coma. Exercise is not recommended for a person with ketosis. It is clear then why high protein, low carbohydrate diets can be potentially dangerous.

HEALTH RISKS ASSOCIATED WITH LOW INTAKES OF PROTEIN

Low intakes of protein can severely impair:

• Growth
• Fighting illness and infection
• Hormone function
• Enzyme function
• Cell building and repair

Illnesses such as KWASHIORKOR or MARAMUS can also occur. KWASHIORKOR is a syndrome due to severe protein deficiency that includes symptoms such as retarded growth, changes in the skin and hair pigment, edema and pathologic changes in the liver. MARAMUS is a condition in which there is a deficiency of both calories and protein, with severe tissue wasting, loss of subcutaneous fat and usually dehydration.

NITROGEN BALANCE TESTS

The proteins of the body are in a state of continuous synthesis (making) and breakdown. In a steady state, when neither growth nor protein loss are occurring protein synthesis is balanced by protein degradation. The continued breakdown and synthesis of protein is termed protein turnover.

If the diet contains more protein than is necessary for protein synthesis, there will be enhanced oxidation of amino acids (and the generation of energy) and an increased excretion of nitrogen (as urea). If, on the other hand, intake of carbohydrate and fat is insufficient to meet energy needs, more protein will be used as a fuel, and less will be available for protein synthesis; thus in a child this will limit growth.

The relationship between dietary protein and requirements can be seen in terms of NITROGEN BALANCE. As the main source of nitrogen is dietary protein, the latter is usually considered synonymous with dietary nitrogen. Similarly, urinary nitrogen is derived from the oxidation of amino acids. This offers a convenient way of studying nitrogen balance, which is the difference between total nitrogen intake and total nitrogen loss. In a healthy adult, the loss of nitrogen equals the dietary intake of nitrogen and the subject is in NITROGEN BALANCE. During growth, or pregnancy, nitrogen intake exceeds nitrogen loss and there is a net increase in total body protein. In contrast, during infection or starvation, there is a net loss of body protein, as intake is insufficient to balance nitrogen loss.

PROTEIN REQUIREMENTS IN DIFFERENT GROUPS

Although many requirements have already been discussed we will briefly look at the athlete, the very young, and the elderly.

Protein requirements are influenced by:

• The digestibility of protein
• The quality of protein

The athlete

Many athletes, particularly those participating in strength and body building related activities are concerned with meeting their protein needs. This concern has led to many athletes to consume large amounts of protein and amino acid supplements to ensure adequate protein intakes. Protein utilisation (and therefore protein requirements) increases with exercise; strength athletes do have higher protein requirements compared to sedentary individuals due to increased synthesis of protein within the body. Actual protein requirements in athletes are influenced by many factors including the composition of the diet, duration and training, ambient temperature, gender and age. However, many studies show that protein intake is usually proportionally higher than the RDA (It is recommended by the COMA panel that adults avoid protein intakes of twice the RNI – intakes above 1.5 g/kg of body weight/day).

The very young

Since children are growing and increasing the total amount for protein in the body, they do have proportional greater requirements for protein than do adults. A child should be in positive nitrogen balance while growing. The amino acid histidine is also deemed “essential” for children as it is required for nitrogen balance and growth.

The elderly

As we get older the acid in our stomach is produced less efficiently and can lead to poor chemical and enzymatic digestion of our food, particularly protein. Food may remain in the stomach longer than normal; it ferments and produces gas (belching) and discomfort. Protein requirements are still essential for the repair and recovery of the body due to illness and the natural process of aging. It may be more suitable though to obtain proteins that are less acidic forming such as meat, and try to complement the diet through fish, and vegetable proteins. These will be more readily absorbed with less stress on the digestive system.

PROTEIN INTAKES

• Sedentary adult: – 0.8g/kg body weight
• Endurance athlete: -1.2-1.4g/kg body weight
• Strength/power athlete: – 1.4-1.8g/kg body weight

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